Low b-value diffusion-weighted imaging: emerging applications in the body

Detection of inflammation in abdominal aortic aneurysm with reduced field-of-view and low-b-value diffusion-weighted imaging

OBJECTIVES

To evaluate the performance of diffusion-weighted imaging (DWI) with an optimal b-value and field-of-view in identifying wall inflammation in abdominal aortic aneurysm (AAA) by comparing it to delayed enhancement T1-weighted imaging (DEI).

METHODS

Twenty-five males with AAA were prospectively enrolled and underwent fat-suppressed T1-weighted dark-blood imaging (T1WI), full field-of-view (f-FOV) and reduced field-of-view (r-FOV) DWI (b values = 0, 100, 400 and 800 s/mm2), and DEI. Corresponding images on f-FOV, r-FOV DWI and DEI at the same level were evaluated qualitatively and quantitatively using the paired t-test and Wilcoxon signed-rank test. The agreement in detecting wall inflammation between DWI and DEI sequences was analyzed using weighted kappa statistics.

RESULTS

For both r-FOV and f-FOV DWI, the scores of delineation of aneurysm wall and lesion conspicuity, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were highest on DWI₁₀₀ (Ps < 0.05). The scores of delineation of aneurysm wall, geometric distortion, lesion conspicuity, and SNR, CNR were significantly higher on r-FOV DWI than those on f-FOV DWI (Ps < 0.05). r-FOV DWI₁₀₀ showed comparable performance to DEI in detecting wall inflammation (κ = 0.715), with superior blood suppression and higher SNR and CNR (Ps < 0.05).

CONCLUSIONS

DWI with r-FOV and low b-value could be a promising alternative to DEI in identifying wall inflammation in AAA.

The Diagnostic Value of Conventional MRI Combined With Diffusion-Weighted Imaging in Microprolactinomas

BACKGROUND

Turbo spin-echo (TSE) diffusion-weighted imaging (DWI) sequences may reduce susceptibility artifacts and image distortion in sellar region, allowing better visualization of small pituitary lesions, and may be used to assist in the diagnosis of pituitary microadenomas.

PURPOSE

To explore the application value of conventional MRI combined with DWI sequences in the diagnosis of microprolactinomas.

STUDY TYPE

Prospective.

POPULATION

Thirty-four patients in microprolactinomas with high signal on T2WI (HT2-PRL) group (34 females, 34 ± 7 years), 26 patients in microprolactinomas with equal or low signal on T2WI (ELT2-PRL) group (21 females, 34 ± 7 years), 35 patients with hyperprolactinemia (33 females, 32 ± 8 years), and 30 normal controls (25 females, 31 ± 7 years).

FIELD STRENGTH/SEQUENCE

TSE sequence at 3 T.

ASSESSMENT

Pituitary morphological parameters (such as length and volume), dynamic contrast-enhanced parameters (such as time to peak) and the apparent diffusion coefficients (ADCs) were measured in each group.

STATISTICAL TESTS

ANOVA and Mann-Whitney U test were used to compare parameters among groups. Spearman's coefficient was used to evaluate the correlation between variables. ROC analysis was used to assess the performance of the parameters. A P-value <0.05 was considered statistically significant.

RESULTS

The pituitary volume of patients in HT2-PRL, ELT2-PRL, and hyperprolactinemia group were 831.00 (747.60, 887.60), 923.63 ± 219.34, and 737.20 (606.40, 836.80) mm3. The pituitary maximum height in these three groups were 7.03 (6.43, 8.63), 8.03 ± 1.41, and 6.63 ± 1.28 mm, respectively. The lesion ADC value was significantly correlated with T2 relative signal intensity (the ratio of signal intensity of microprolactinoma or anterior pituitary to left temporal cortex) (r = 0.821). Compared with patients with hyperprolactinemia, the diagnostic efficacy of T2 relative signal intensity was higher in HT2-PRL group, with an AUC of 0.954, whereas the ADC value was the highest in ELT2-PRL group, with an AUC of 0.924.

CONCLUSION

DWI sequences can be used to assist in the diagnosis of pituitary microadenomas.

EVIDENCE LEVEL

1 TECHNICAL EFFICACY: Stage 2.

Excessive interstitial free-water in cortical gray matter preceding accelerated volume changes in individuals at clinical high risk for psychosis

Recent studies show that accelerated cortical gray matter (GM) volume reduction seen in anatomical MRI can help distinguish between individuals at clinical high risk (CHR) for psychosis who will develop psychosis and those who will not. This reduction is suggested to represent atypical developmental or degenerative changes accompanying an accumulation of microstructural changes, such as decreased spine density and dendritic arborization. Detecting the microstructural sources of these changes before they accumulate into volume loss is crucial. Our study aimed to detect these microstructural GM alterations using diffusion MRI (dMRI). We tested for baseline and longitudinal group differences in anatomical and dMRI data from 160 individuals at CHR and 96 healthy controls (HC) acquired in a single imaging site. Of the CHR individuals, 33 developed psychosis (CHR-P), while 127 did not (CHR-NP). Among all participants, longitudinal data was available for 45 HCs, 17 CHR-P, and 66 CHR-NP. Eight cortical lobes were examined for GM volume and GM microstructure. A novel dMRI measure, interstitial free water (iFW), was used to quantify GM microstructure by eliminating cerebrospinal fluid contribution. Additionally, we assessed whether these measures differentiated the CHR-P from the CHR-NP. In addition, for completeness, we also investigated changes in cortical thickness and in white matter (WM) microstructure. At baseline the CHR group had significantly higher iFW than HC in the prefrontal, temporal, parietal, and occipital lobes, while volume was reduced only in the temporal lobe. Neither iFW nor volume differentiated between the CHR-P and CHR-NP groups at baseline. However, in many brain areas, the CHR-P group demonstrated significantly accelerated changes (iFW increase and volume reduction) with time than the CHR-NP group. Cortical thickness provided similar results as volume, and there were no significant changes in WM microstructure. Our results demonstrate that microstructural GM changes in individuals at CHR have a wider extent than volumetric changes or microstructural WM changes, and they predate the acceleration of brain changes that occur around psychosis onset. Microstructural GM changes, as reflected by the increased iFW, are thus an early pathology at the prodromal stage of psychosis that may be useful for a better mechanistic understanding of psychosis development.

Diffuse-Type Tenosynovial Giant Cell Tumor: What Are the Important Findings on the Initial and Follow-Up MRI?

Tenosynovial giant cell tumor (TSGCT) is a rare soft tissue tumor that involves the synovial lining of joints, bursae, and tendon sheaths, primarily affecting young patients (usually in the fourth decade of life). The tumor comprises two subtypes: the localized type (L-TSGCT) and the diffuse type (D-TSGCT). Although these subtypes share histological and genetic similarities, they present a different prognosis. D-TSGCT tends to exhibit local aggressiveness and a higher recurrence rate compared to L-TSGCT. Magnetic resonance imaging (MRI) is the preferred diagnostic tool for both the initial diagnosis and for treatment planning. When interpreting the initial MRI of a suspected TSGCT, it is essential to consider: (i) the characteristic findings of TSGCT-evident as low to intermediate signal intensity on both T1- and T2-weighted images, with a blooming artifact on gradient-echo sequences due to hemosiderin deposition; (ii) the possibility of D-TSGCT-extensive involvement of the synovial membrane with infiltrative margin; and (iii) the resectability and extent-if resectable, synovectomy is performed; if not, a novel systemic therapy involving colony-stimulating factor 1 receptor inhibitors is administered. In the interpretation of follow-up MRIs of D-TSGCTs after treatment, it is crucial to consider both tumor recurrence and potential complications such as osteoarthritis after surgery as well as the treatment response after systemic treatment. Given its prevalence in young adult patents and significant impact on patients' quality of life, clinical trials exploring new agents targeting D-TSGCT are currently underway. Consequently, understanding the characteristic MRI findings of D-TSGCT before and after treatment is imperative.

Imaging Techniques and Clinical Application of the Marrow-Blood Barrier in Hematological Malignancies

The pathways through which mature blood cells in the bone marrow (BM) enter the blood stream and exit the BM, hematopoietic stem cells in the peripheral blood return to the BM, and other substances exit the BM are referred to as the marrow-blood barrier (MBB). This barrier plays an important role in the restrictive sequestration of blood cells, the release of mature blood cells, and the entry and exit of particulate matter. In some blood diseases and tumors, the presence of immature cells in the blood suggests that the MBB is damaged, mainly manifesting as increased permeability, especially in angiogenesis. Some imaging methods have been used to monitor the integrity and permeability of the MBB, such as DCE-MRI, IVIM, ASL, BOLD-MRI, and microfluidic devices, which contribute to understanding the process of related diseases and developing appropriate treatment options. In this review, we briefly introduce the theory of MBB imaging modalities along with their clinical applications.

Microstructural Cortical Gray Matter Changes Preceding Accelerated Volume Changes in Individuals at Clinical High Risk for Psychosis

Recent studies show that accelerated cortical gray matter (GM) volume reduction seen in anatomical MRI can help distinguish between individuals at clinical high risk (CHR) for psychosis who will develop psychosis and those who will not. This reduction is thought to result from an accumulation of microstructural changes, such as decreased spine density and dendritic arborization. Detecting the microstructural sources of these changes before they accumulate is crucial, as volume reduction likely indicates an underlying neurodegenerative process. Our study aimed to detect these microstructural GM alterations using diffusion MRI (dMRI). We tested for baseline and longitudinal group differences in anatomical and dMRI data from 160 individuals at CHR and 96 healthy controls (HC) acquired in a single imaging site. Eight cortical lobes were examined for GM volume and GM microstructure. A novel dMRI measure, interstitial free water (iFW), was used to quantify GM microstructure by eliminating cerebrospinal fluid contribution. Additionally, we assessed whether these measures differentiated the 33 individuals at CHR who developed psychosis (CHR-P) from the 127 individuals at CHR who did not (CHR-NP). At baseline the CHR group had significantly higher iFW than HC in the prefrontal, temporal, parietal, and occipital lobes, while volume was reduced only in the temporal lobe. Neither iFW nor volume differentiated between the CHR-P and CHR-NP groups at baseline. However, in most brain areas, the CHR-P group demonstrated significantly accelerated iFW increase and volume reduction with time than the CHR-NP group. Our results demonstrate that microstructural GM changes in individuals at CHR have a wider extent than volumetric changes and they predate the acceleration of brain changes that occur around psychosis onset. Microstructural GM changes are thus an early pathology at the prodromal stage of psychosis that may be useful for early detection and a better mechanistic understanding of psychosis development.

Detection of bone marrow metastases in children and young adults with solid cancers with diffusion-weighted MRI

OBJECTIVE

To compare the diagnostic accuracy of diffusion-weighted (DW)-MRI with b-values of 50 s/mm2 and 800 s/mm2 for the detection of bone marrow metastases in children and young adults with solid malignancies.

METHODS

In an institutional review board-approved prospective study, we performed 51 whole-body DW-MRI scans in 19 children and young adults (14 males, 5 females; age range: 1-25 years) with metastasized cancers before (n = 19 scans) and after (n = 32 scans) chemotherapy. Two readers determined the presence of focal bone marrow lesions in 10 anatomical areas. A third reader measured ADC and SNR of focal lesions and normal marrow. Simultaneously acquired 18F-FDG-PET scans served as the standard of reference. Data of b = 50 s/mm2 and 800 s/mm2 images were compared with the Wilcoxon signed-rank test. Inter-reader agreement was evaluated with weighted kappa statistics.

RESULTS

The SNR of bone marrow metastases was significantly higher compared to normal bone marrow on b = 50 s/mm2 (mean ± SD: 978.436 ± 1239.436 vs. 108.881 ± 109.813, p < 0.001) and b = 800 s/mm2 DW-MRI (499.638 ± 612.721 vs. 86.280 ± 89.120; p < 0.001). On 30 out of 32 post-treatment DW-MRI scans, reconverted marrow demonstrated low signal with low ADC values (0.385 × 10-3 ± 0.168 × 10-3mm2/s). The same number of metastases (556/588; 94.6%; p > 0.99) was detected on b = 50 s/mm2 and 800 s/mm2 images. However, both normal marrow and metastases exhibited low signals on ADC maps, limiting the ability to delineate metastases. The inter-reader agreement was substantial, with a weighted kappa of 0.783 and 0.778, respectively.

CONCLUSION

Bone marrow metastases in children and young adults can be equally well detected on b = 50 s/mm2 and 800 s/mm2 images, but ADC values can be misleading.

Technical Advancements in Abdominal Diffusion-weighted Imaging

Since its first observation in the 18th century, the diffusion phenomenon has been actively studied by many researchers. Diffusion-weighted imaging (DWI) is a technique to probe the diffusion of water molecules and create a MR image with contrast based on the local diffusion properties. The DWI pixel intensity is modulated by the hindrance the diffusing water molecules experience. This hindrance is caused by structures in the tissue and reflects the state of the tissue. This characteristic makes DWI a unique and effective tool to gain more insight into the tissue's pathophysiological condition. In the past decades, DWI has made dramatic technical progress, leading to greater acceptance in clinical practice. In the abdominal region, however, acquiring DWI with good quality is challenging because of several reasons, such as large imaging volume, respiratory and other types of motion, and difficulty in achieving homogeneous fat suppression. In this review, we discuss technical advancements from the past decades that help mitigate these problems common in abdominal imaging. We describe the use of scan acceleration techniques such as parallel imaging and compressed sensing to reduce image distortion in echo planar imaging. Then we compare techniques developed to mitigate issues due to respiratory motion, such as free-breathing, respiratory-triggering, and navigator-based approaches. Commonly used fat suppression techniques are also introduced, and their effectiveness is discussed. Additionally, the influence of the abovementioned techniques on image quality is demonstrated. Finally, we discuss the current and future clinical applications of abdominal DWI, such as whole-body DWI, simultaneous multiple-slice excitation, intravoxel incoherent motion, and the use of artificial intelligence. Abdominal DWI has the potential to develop further in the future, thanks to scan acceleration and image quality improvement driven by technological advancements. The accumulation of clinical proof will further drive clinical acceptance.

Effectiveness of functional magnetic resonance imaging for early identification of chronic kidney disease: A systematic review and network meta-analysis

PURPOSE

The commonly used clinical indicators are not sensitive enough on detecting early chronic kidney disease (CKD), whether functional magnetic resonance imaging (fMRI) can be regarded as a new noninvasive method to identify early stages of CKD and even different stages remains unknown. We performed a network meta-analysis to explore the question.

METHODS

Five databases were searched to identify eligible articles from 2000 to 2022. The outcome indicators were imaging biomarkers of fMRI techniques, including apparent diffusion coefficient (ADC) by diffusion-weighted imaging (DWI), fractional anisotropy (FA) by diffusion tensor imaging (DTI), diffusion coefficient (D), pseudodiffusion coefficient (D*), and perfusion fraction (f) by intravoxel incoherent motion imaging (IVIM), and apparent relaxation rate (R2*) by blood oxygen level-dependent (BOLD).

RESULTS

A total of 21 articles with 1472 patients were included for analysis. Cortical FA, f, and R2* values in CKD stages 1-2 were found statistically different with healthy controls (mean difference (MD), -0.03, 95% confidence interval (CI) -0.05, -0.01; MD, -0.04, 95% CI -0.06, -0.02; MD, 2.22, 95% CI 0.87, 3.57, respectively), and cortical ADC values were significantly different among different CKD stages (stages 3 and 1-2: MD, -0.15, 95% CI -0.23, -0.06; stages 4-5 and 3: MD -0.27, 95% CI -0.39, -0.14).

CONCLUSION

The results indicated fMRI techniques had great efficacy in assessing early stages and different stages of CKD, among which DTI, IVIM, and BOLD exerted great superiority in differentiating early CKD patients from the general population, while DWI showed the advantage in distinguishing different CKD stages.

Directional and inter-acquisition variability in diffusion-weighted imaging and editing for restricted diffusion

PURPOSE

To evaluate and quantify inter-directional and inter-acquisition variation in diffusion-weighted imaging (DWI) and emphasize signals that report restricted diffusion to enhance cancer conspicuity, while reducing the effects of local microscopic motion and magnetic field fluctuations.

METHODS

Ten patients with biopsy-proven prostate cancer were studied under an Institutional Review Board-approved protocol. Individual acquisitions of DWI signal intensities were reconstructed to calculate inter-acquisition distributions and their statistics, which were compared for healthy versus cancer tissue. A method was proposed to detect and filter the acquisitions affected by motion-induced signal loss. First, signals that reflect restricted diffusion were separated from the acquisitions that suffer from signal loss, likely due to microscopic motion, by imposing a cutoff value. Furthermore, corrected apparent diffusion coefficient maps were calculated by employing a weighted sum of the multiple acquisitions, instead of conventional averaging. These weights were calculated by applying a soft-max function to the set of acquisitions per-voxel, making the analysis immune to acquisitions with significant signal loss, even if the number of such acquisitions is high.

RESULTS

Inter-acquisition variation is much larger than the Rician noise variance, local spatial variations, and the estimates of diffusion anisotropy based on the current data, as well as the published values of anisotropy. The proposed method increases the contrast for cancers and yields a sensitivity of98 . 8 % $$ 98.8\% $$ with a false positive rate of3 . 9 % $$ 3.9\% $$ .

CONCLUSION

Motion-induced signal loss makes conventional signal-averaging suboptimal and can obscure signals from areas with restricted diffusion. Filtering or weighting individual acquisitions prior to image analysis can overcome this problem.

Free-Breathing Liver Magnetic Resonance Imaging With Respiratory Frequency-Modulated Continuous-Wave Radar-Trigger Technique: A Preliminary Study

Purpose

The aim of this study is to evaluate the performance of free-breathing liver MRI with a novel respiratory frequency-modulated continuous-wave radar-trigger (FT) technique on T2-weighted imaging (T2WI) and diffusion-weighted imaging (DWI) for both healthy volunteers and patients in comparison to navigator-trigger (NT) and belt-trigger (BT) techniques.

Methods

In this prospective study, 17 healthy volunteers and 23 patients with known or suspected liver diseases were enrolled. Six sequences (T2WI and DWI with FT, NT, and BT techniques) were performed in each subject. Quantitative evaluation and qualitative assessment were analyzed by two radiologists. Overall image quality, blurring, motion artifacts, and liver edge delineations were rated on a 4-point Likert scale. The liver and lesion signal-to-noise ratio (SNR), the lesion-to-liver contrast-to-noise ratio (CNR), as well as the apparent diffusion coefficient (ADC) value were quantitatively calculated.

Results

For volunteers, there were no significant differences in the image quality Likert scores and quantitative parameters on T2WI and DWI with three respiratory-trigger techniques. For patients, NT was superior to other techniques for image quality on T2WI; conversely, little difference was found on DWI in qualitative assessment. The mean SNR of the liver on T2WI and DWI with BT, NT, and FT techniques was similar in patients, which is in line with volunteers. FT performed better in terms of higher SNR (705.13 ± 434.80) and higher CNR (504.41 ± 400.69) on DWI at b50 compared with BT (SNR: 651.83 ± 401.16; CNR:429.24 ± 404.11) and NT (SNR: 639.41 ± 407.98; CNR: 420.64 ± 416.61) (p < 0.05). The mean ADC values of the liver and lesion with different techniques in both volunteers and patients showed non-significant difference.

Conclusion

For volunteers, the performance of T2WI as well as DWI with three respiratory-trigger techniques was similarly good. As for patients, FT-DWI is superior to BT and NT techniques in terms of higher lesion SNR and CNR at b50.

Myocardium microcirculation study in a healthy Chinese population using 3.0-T cardiac magnetic resonance intravoxel incoherent motion imaging

BACKGROUND

Intravoxel incoherent motion imaging (IVIM) can non-invasively evaluate diffusion and microvascular perfusion.

PURPOSE

To explore the myocardium microcirculation of a healthy Chinese population by using cardiac magnetic resonance (CMR) IVIM.

MATERIAL AND METHODS

A total of 80 healthy volunteers (44 men, 36 women) who underwent 3.0-T CMR examination were enrolled. All participants had cardiac cine imaging and short-axis CMR-IVIM of the left ventricle (LV) using multiple b-values. The consistency of the IVIM parameters was assessed by intraclass correlation coefficient (ICC) and the Bland-Altman test. Spearman correlation analysis was performed between IVIM parameters and age, and body mass index (BMI). The differences of IVIM parameters were analyzed between gender and different ages.

RESULTS

LV end-diastolic volume (EDV), end-systolic volume (ESV), LVmass, cardiac output (CO), and BMI in the male group were higher than those in the female group (P<0.05). IVIM parameters had good intra-observer and inter-observer consistency (≥0.75). Bland-Altman analysis also showed good intra-observer and inter-observer consistency. ADC_fast decreased with increasing female age (rs = -0.37; P = 0.01), while IVIM parameters had no correlation with BMI regardless of sex. ADC_fast in the female group had a statistical difference between different age groups. The ADC_slow and f in the male group were lower than those in the female group (P<0.05); however, there was no statistical difference in ADC_fast between genders.

CONCLUSION

IVIM parameters in healthy Chinese volunteers provided good consistency. There was a negative correlation between ADC_fast and age in the female group.

Study of bone marrow microstructure in healthy young adults using intravoxel incoherent motion diffusion-weighted MRI

Bone marrow is one of the most important organs in the human body. The evaluation of bone marrow microstructure and gender-related cellular and capillary networks in healthy young adults can help to better understand the process of bone metabolism. Intravoxel incoherent motion (IVIM) provides both diffusion and perfusion quantifications without requiring intravenous contrast agent injection. In this prospective study, 60 healthy young age-matched volunteers (30 men and 30 women) underwent MRI scans at 1.5 T using multi-b-value diffusion-weighted imaging on sagittal planes covering the lumbar bone marrow. The apparent diffusion coefficient (ADC), true ADC (D), pseudo-ADC (D*), and perfusion fraction (f) were calculated from the diffusion-weighted images using the mono- and bi-exponential models. Lumbar cancellous bone (L2-L4) was selected as the region of interest. An independent t-test was used to detect significant differences in ADC values and IVIM parameters between men and women. The differences in IVIM parameters among the L2, L3, and L4 groups were compared with analysis of variance. The D and f values in women were significantly higher than that in men (p = 0.001, 0.026). However, D* was significantly lower in women than that in men (p = 0.001). Furthermore, there was no significant gender difference for the conventional ADC value (p = 0.186). Moreover, there were no significant differences in the D, f, and D* values among the L2, L3, and L4 vertebras of women or men. IVIM parameters can show differences in bone marrow between young women and men. As a non-invasive method, it can assess bone marrow microstructure, such as cellularity and perfusion.

Simplified intravoxel incoherent motion diffusion-weighted MRI of liver lesions: feasibility of combined two-colour index maps

Background

To evaluate the feasibility of two-colour index maps containing combined diffusion and perfusion information from simplified intravoxel incoherent motion (IVIM) for liver lesion malignancy assessment.

Methods

Diffusion-weighted data from a respiratory-gated 1.5-T magnetic resonance sequence were analysed in 109 patients with liver lesions. With three b values (0, 50, 800 s/mm²) estimated diffusion coefficient D′, perfusion fraction f′, and apparent diffusion coefficient (ADC) maps were calculated and analysed for regions of interest (ROIs). D′ and f′ cutoff values were determined by differentiating haemangiomas from other lesions and focal nodular hyperplasias from other lesions, respectively. Combined I_Df index maps were generated with a voxel value set to 100, if both D′ and f′ voxel values were lower than their cutoff values (1,529.4 × 10^-6 mm²/s and 114.4 × 10^-3, respectively), otherwise to 0. Moreover, I_ADC index maps were generated from ADC cutoff value (1,338.5 × 10^-6 mm²/s) obtained by differentiating benign from malignant lesions. Discriminatory power was assessed for both I_Df and I_ADC. Index maps were displayed as two-colour overlays to b-800 images and visually assessed within the translucent hyperintense areas.

Results

For I_Df, the same diagnostic accuracy was achieved as for the combined use of parameters D′ and f′ (93.6%). Compared to I_ADC, I_Df showed a higher diagnostic accuracy. Visual judgment of I_Df yielded an accuracy (95.4%) similar to that of quantitative analysis (93.6%).

Conclusion

Voxel-wise combined two-colour index maps I_Df provide similar diagnostic accuracy as ROI-based combination of estimated IVIM parameters D′ and f′ and are suitable for visual assessment of liver lesion malignancy.

Multi-shot Diffusion-Weighted MRI With Multiplexed Sensitivity Encoding (MUSE) in the Assessment of Active Inflammation in Crohn's Disease

BACKGROUND

Single-shot diffusion-weighted imaging (ssDWI) has been shown useful for detecting active bowel inflammation in Crohn's disease (CD) without MRI contrast. However, ssDWI suffers from geometric distortion and low spatial resolution.

PURPOSE

To compare conventional ssDWI with higher-resolution ssDWI (HR-ssDWI) and multi-shot DWI based on multiplexed sensitivity encoding (MUSE-DWI) for evaluating bowel inflammation in CD, using contrast-enhanced MR imaging (CE-MRI) as the reference standard.

STUDY TYPE

Prospective.

SUBJECTS

Eighty nine patients with histological diagnosis of CD from previous endoscopy (55 male/34 female, age: 17-69 years). FIELD STRENGTH/SEQUENCES: ssDWI (2.7 mm × 2.7 mm), HR-ssDWI (1.8 mm × 1.8 mm), MUSE-DWI (1.8 mm × 1.8 mm) based on echo-planar imaging, T2-weighted imaging, and CE-MRI sequences, all at 1.5 T.

ASSESSMENT

Five raters independently evaluated the tissue texture conspicuity, geometry accuracy, minimization of artifacts, diagnostic confidence, and overall image quality using 5-point Likert scales. The diagnostic performance (sensitivity, specificity and accuracy) of each DWI sequences was assessed on per-bowel-segment basis.

STATISTICAL TESTS

Inter-rater agreement for qualitative evaluation of each parameter was measured by the intra-class correlation coefficient (ICC). Paired Wilcoxon signed-rank tests were performed to evaluate the statistical significance of differences in qualitative scoring between DWI sequences. A P value <0.05 was considered to be statistically significant.

RESULTS

Tissue texture conspicuity, geometric distortions, and overall image quality were significantly better for MUSE-DWI than for ssDWI and HR-ssDWI with good agreement among five raters (ICC: 0.70-0.89). HR-ssDWI showed significantly poorer performance to ssDWI and MUSE-DWI for all qualitative scores and had the worst diagnostic performance (sensitivity of 57.0% and accuracy of 87.3%, with 36 undiagnosable cases due to severe artifacts). MUSE-DWI showed significantly higher sensitivity (97.5% vs. 86.1%) and accuracy (98.9% vs. 95.1%) than ssDWI for detecting bowel inflammation.

DATA CONCLUSION

MUSE-DWI was advantageous in assessing bowel inflammation in CD, resulting in improved spatial resolution and image quality.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY STAGE: 2.

Detection of mural inflammation with low b-value diffusion-weighted imaging in patients with active Takayasu Arteritis

OBJECTIVES

To evaluate the performance of low b-value diffusion-weighted imaging (DWI) for detection of inflamed vessels in active Takayasu arteritis (TA).

METHODS

Forty patients with active TA involving the thoracic aorta and its super-aortic branches underwent low b-value (50 s/mm²) DWI, T2-weighted imaging (T2WI), and delayed enhancement T1-weighted imaging (DEI). Corresponding images on these 3 sequences at the same diseased level were evaluated qualitatively and quantitatively using Friedman and Kruskal-Wallis test, and the agreement between them in detection of inflamed vessels was assessed using Cochran's Q test.

RESULTS

The overall image quality of DEI, DWI, and T2WI was scored 7.97 ± 1.15, 7.32 ± 1.73, and 6.51 ± 1.69 respectively. The score of DEI and DWI was higher than that of T2WI (p < 0.001). The quality of blood suppression was rated higher in DWI than T2WI and DEI (p < 0.001). Both the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the diseased vessel walls measured on DEI and DWI were significantly higher than those on T2WI (p < 0.001). However, there was no significant difference in SNR and CNR between DEI and DWI (p = 0.283 and 0.063). In detection of mural inflammation, significant advantage was observed when comparing the findings from DEI/DWI to those from T2WI (p < 0.001). But no significant difference was found between the findings of DWI and DEI (p > 0.99).

CONCLUSIONS

Low b-value DWI may be used as a promising alternative to DEI for detecting inflamed vessels in active TA.

KEY POINTS

• Currently, the most widely used imaging modality in detection of mural inflammation is contrast-enhanced MRI. • Low b-value DWI is shown comparable to contrast-enhanced MRI and superior to T2WI in identifying mural inflammation in patients with active Takayasu arteritis. • Low b-value DWI is a fast and unenhanced MRI technique which may potentially replace contrast-enhanced MRI in identifying disease activity of Takayasu arteritis.

The value of multiparametric histogram features based on intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI) for the differential diagnosis of liver lesions

Background

The present study analyzed whole-lesion histogram parameters from intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI) to explore the clinical value of IVIM histogram features in the differentiation of liver lesions.

Methods

In this retrospective study, 33 cases of hepatic hemangioma (HH), 22 cases of hepatic cysts (HC), and 34 cases of hepatocellular carcinoma (HCC) were underwent IVIM-DWI (b =0–600 s/mm²), which were confirmed pathologically and clinically. The data were processed by IVIM model to obtain the following quantitative indicators: perfusion fraction (f), slow diffusion coefficient (D), and pseudo-diffusion coefficient (or fast diffusion coefficient, D*). The region of interest in the largest solid part of the lesion was delineated for histogram analysis of the correlation between tissue image and lesion type. The relevant histogram parameters were obtained and statistically analyzed. The characteristic histogram parameters for HH, HC, and HCC were compared to find significantly different parameters. The diagnostic efficacies of these parameters for HH, liver cysts, and HCC were assessed using the receiver operating characteristic (ROC) curves.

Results

There were significant differences in the maximum diameter, maximum value, minimum value, mean, median, standard deviation, uniformity, skewness, kurtosis, volume, 10th percentile (P10) of D, and 90th percentile (P90) of D between the three groups (P<0.05). The maximum diameter, minimum value, entropy, and volume of D* differed significantly between the three groups (P<0.05). The maximum diameter, minimum value, mean, median, skewness, kurtosis, volume, P10, and P90 of f differed significantly between the three groups (P<0.05). The largest area under the ROC curve (AUC) for both D* and f was that of volume (AUC =0.883 for both). When 1438.802 was used as the volume cut-off, the sensitivity and specificity of volume in differentiating between HH and HC were 87.88 and 77.27, respectively, and the sensitivity and specificity of volume in differentiating between HC and HCC were 77.27 and 85.29.

Conclusions

A multiparametric histogram from IVIM-DWI magnetic resonance imaging (MRI) is an effective means of identifying HH, HC, and HCC that provides valuable reference information for clinical diagnosis.

Beyond the brain: Extra-axial pathology on diffusion weighted imaging in neuroimaging

Diffusion-weighted imaging (DWI) has a central role in the assessment of the brain parenchyma, particularly in the context of acute stroke. However, the applications of DWI extend far beyond the brain parenchyma and include the assessment of the extra-axial structures of the head and neck that are included in routine brain imaging. In this pictorial review, the added-value of DWI over other conventional sequences is illustrated through discussion of a broad range of disorders affecting the vasculature, skull, orbits, nasal cavity and salivary glands. This article highlights the requirement for all structures, both intra- and extra-axial, to be carefully reviewed on DWI.

Preoperative detection of colorectal liver metastases: DWI alone or combined with MDCT is no substitute for Gd-EOB-DTPA-enhanced MRI

Background

Magnetic resonance imaging (MRI) with hepatocyte specific contrast has the highest sensitivity for colorectal liver metastases but comes at high costs and long examination times.

Purpose

To evaluate if preoperative detection of colorectal liver metastases with less resource-consuming diffusion-weighted imaging (DWI) alone or in combination with multidetector computed tomography (MDCT) can compete with gadolinium-etoxybenzyl-diethylenetriaminepentaacetic acid (Gd-EOB-DTPA)-enhanced MRI.

Material and Methods

Forty-four patients with 123 colorectal liver metastases received MDCT and Gd-EOB-DTPA-enhanced MRI including DWI before liver resection for colorectal liver metastases. Five image sets were evaluated by two radiologists. The DWI set consisted of DWI, ADC map, coronal, axial T2-weighted single-shot sequences. The DWI-T2F set contained additionally respiratory-triggered T2-weighted TSE-SPIR sequences. The MDCT set consisted of four-phase MDCT, the MDCT-DWI set also contained DWI. The CE-MRI set contained all MRI sequences including Gd-EOB-DTPA. Reference standards was histopathology and follow-up.

Results

CE-MRI set had highest sensitivity ( P ≤ 0.013) with 95% compared to 72%, 73%, 73%, and 87% the for DWI set, DWI-T2W-FS set, MDCT set, and MDCT-DWI set, respectively. The CE-MRI set had the highest sensitivity ( P≤0.012) for colorectal liver metastases <10 mm with 87% compared to 55%, 52%, 23%, and 58% for the DWI set, DWI-T2W-FS set, MDCT set, and MDCT-DWI set, respectively. The MDCT-DWI set improved sensitivity overall and in size-dependent subgroup analyses compared to the MDCT set ( P ≤ 0.031). The MDCT-DWI set showed the highest specificity of 98% followed by 98%, 98%, 95%, and 88% for the DWI set, DWI-T2W-FS set, MDCT set, and CE-MRI set, respectively.

Conclusion

The less resource and time-consuming DWI sets are inferior to Gd-EOB-DTPA-enhanced MRI for the detection of colorectal liver metastases. Gd-EOB-DTPA-enhanced MRI with its excellent sensitivity should be the preferred preoperative modality when meticulous lesion identification is essential. Combination of DWI with MDCT improved significantly sensitivity compared to each modality alone.

Effect of granulocyte colony-stimulating factor on bone marrow: evaluation by intravoxel incoherent motion and dynamic contrast-enhanced magnetic resonance imaging

OBJECTIVE

To report our experience with the use of intravoxel incoherent motion (IVIM) magnetic resonance imaging (MRI) and dynamic contrast-enhanced (DCE)-MRI in bone marrow before and after administration of granulocyte colony-stimulating factor (GCSF). Moreover, a small series of patients with bone metastases from breast cancer have been evaluated by IVIM DW-MRI and DCE-MRI before and after GCSF administration.

MATERIALS AND METHODS

We studied with IVIM-MRI and DCE-MRI 14 patients with rectal or uterine cervix cancer studied before and 4-18 days after administration of GCSF; the second MR examination was obtained after three chemotherapy courses. IVIM perfusion fraction (f), pseudo-diffusion coefficient (D*), true diffusion coefficient (D) and apparent diffusion coefficient (ADC) as well area under the curve at 60 s (AUC60) were calculated for bone marrow before and after GCSF administration. Moreover, two different IVIM parametric maps (i.e., ADC and ADC_low) were generated by selecting two different intervals of b values (0-1000 and 0-80, respectively). Furthermore, four patients affected by pelvic bone metastases from breast adenocarcinoma who received GCSF administration were also qualitatively evaluated for evidence of lesions on ADC maps, ADC_low maps and DCE-MRI.

RESULTS

ADC, D, D*, f and AUC60 values were significantly higher in hyperplastic bone marrow than in untreated bone marrow (p values < 0.0001, < 0.0001, < 0.001, < 0.001, < 0.0001, respectively). All bone metastases were clearly differentiable from hyperplastic bone marrow on ADC_low maps, but not on ADC maps and DCE-MRI.

CONCLUSION

MR functional imaging techniques, such as DW-, IVIM DW- and DCE-MRI are effective tools in assessing the response of bone marrow to the administration of growth factors. Although an overlap between signal of hyperplastic bone marrow and lytic bone metastases can occur on ADC maps and DCE-MRI, evaluation of ADCl_ow maps by IVIM DW-MRI could permit to differentiate hyperplastic bone marrow from lytic bone metastases. Further studies are needed to confirm our data.

STROBE-A preliminary investigation of IVIM-DWI in cardiac imaging

This study aims to explore the possibility to apply intravoxel incoherent motion-magnetic resonance imaging (IVIM-MRI) in cardiac imaging.Multi-b-value diffusion-weighted imaging (DWI) sequence scanning was performed on 12 healthy volunteers. A double exponential model was adopted, and the b-value sequence was 0, 20, 60, 80, 120, 200, and 600 second/mm. The D-value, D*-value, and f-value of the anterior posterior and lateral walls of the ventricular septum were respectively measured on the short axis section of the heart, the parameters of the myocardium in different blood supply areas in each segment were recorded, and the measured data of these different segments were compared using analysis of variance.Among these 12 healthy volunteers, the D-value, D*-value, and f-value of these 72 segments were not exactly equal, the D-values of the myocardium in the 5th and 11th segment were lower than those in the 2nd, 3rd, 8th, and 9th segments, and the pairwise differences were statistically significant (P < .001). Furthermore, the difference in D-value between the 5th and 11th segments was not statistically significant (P = 1.000). The D*-value and f-value of the myocardium in the 5th and 11th segment were higher than those in the 2nd, 3rd, 8th, and 9th segments, and the pairwise differences were statistically significant (P < .001). Furthermore, the differences in D*-value and f-value between the 5th and 11th segments was not statistically significant (P = .214, .787).The intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI) technique can quantitatively reflect the diffusion and blood perfusion status of the myocardium.

Hepatic pseudolymphoma: imaging features on dynamic contrast-enhanced MRI and diffusion-weighted imaging

PURPOSE

To investigate dynamic contrast-enhanced (DCE) MR findings and diffusion-weighted imaging (DWI) characteristics of hepatic pseudolymphoma.

MATERIALS AND METHODS

The MR data of 20 lesions in 14 patients with histopathologically proven hepatic pseudolymphoma were retrospectively analyzed. All patients underwent dynamic gadopentetate dimeglumine-enhanced MR imaging and DWI. Morphologic characteristics and signal features on T1- and T2-weighted images (T1WI, T2WI), and DCE pattern were qualitatively evaluated. The quantitative analysis was performed for the size, the degree of enhancement on arterial phase, signal intensity (SI) of DWI, and apparent diffusion coefficient (ADC) values. The Wilcoxon signed ranks test was used for statistical analysis.

RESULTS

The contour of all lesions was round. The lesion size was 0.7-2.8 cm (mean 1.3 ± 0.5 cm). All lesions manifested as homogeneous hypointensity on T1WI and hyperintensity on T2WI. All lesions were shown as hypervascular with various enhancement patterns on DCE MR imaging. The presence of peripheral enhancement and pseudocapsule was observed in 7 and 4 lesions, respectively. SI of the hepatic pseudolymphoma was significantly lower than that of portal vein on arterial phase (P < 0.001) and the ADC was significantly lower than that of spleen (P = 0.012).

CONCLUSION

A homogeneous nodule with small size (<2 cm), manifestation of hypervascular with lower SI than that of portal vein on arterial phase and lower ADC values than that of spleen are the common MR features of hepatic pseudolymphoma.

Conspicuity of Malignant Liver Tumors on Diffusion-Weighted Imaging With Short tau Inversion Recovery After Gadolinium Ethoxybenzyl Diethylenetriaminepentaacetic Acid Administration

BACKGROUND

Diffusion-weighted imaging (DWI) has been used for the detection and characterization of liver tumors because it has excellent contrast resolution. DWI using short tau inversion recovery (STIR) can improve tumor-to-liver contrast after gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid (Gd-EOB-DTPA) administration that shortens the T₁ relaxation of liver parenchyma.

PURPOSE

To quantitatively and qualitatively compare the conspicuity of malignant liver tumors on DWI after Gd-EOB-DTPA administration between STIR and chemical shift selective (CHESS) sequences.

STUDY TYPE

Single-institution retrospective study.

SUBJECTS

Fifty-seven patients with histologically confirmed malignant liver tumors were evaluated.

FIELD STRENGTH/SEQUENCE

Low b-value DWIs with STIR and CHESS sequences 18-20 minutes after Gd-EOB-DTPA administration were acquired at 1.5T.

ASSESSMENT

Tumor contrast-to-noise ratio (CNR) and visual grade of tumor conspicuity on DWI between STIR and CHESS sequences were compared.

STATISTICAL TESTS

Paired Student's t-test and the Wilcoxon signed rank-test were applied. P < 0.05 was considered statistically significant.

RESULTS

The mean tumor CNR and visual grade of tumor conspicuity on DWI were significantly higher for STIR than for CHESS (both P < 0.001). Regardless of the presence of chronic liver disease, the mean CNR (normal liver 33.5 ± 19.8 vs. 15.7 ± 12.2, P < 0.001; chronic liver disease 19.6 ± 11.0 vs. 9.2 ± 7.8, P < 0.001) and the visual conspicuity grade (normal liver 3.36 ± 0.64 vs. 2.56 ± 0.77, P < 0.001; chronic liver disease 2.94 ± 0.80 vs. 2.25 ± 0.84, P = 0.001) were significantly higher for STIR than for CHESS. Mean CNR and the visual conspicuity grade were also significantly higher for STIR than for CHESS in patients with hepatocellular carcinomas (CNR 18.1 ± 10.5 vs. 8.8 ± 7.2, P < 0.001; visual grade 2.88 ± 0.83 vs. 2.22 ± 0.87, P = 0.001) or metastases (CNR 35.0 ± 19.3 vs. 16.2 ± 13.1, P < 0.001; visual grade 3.45 ± 0.51 vs. 2.59 ± 0.73, P < 0.001).

DATA CONCLUSION

DWI using STIR may be more helpful for depicting malignant liver tumors after Gd-EOB-DTPA administration compared with DWI using CHESS.

LEVEL OF EVIDENCE

3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:565-573.

Accurate IVIM model-based liver lesion characterisation can be achieved with only three b-value DWI

OBJECTIVE

The objective of this study was to evaluate a simplified intravoxel incoherent motion (IVIM) approach of diffusion-weighted imaging (DWI) with four b-values for liver lesion characterisation at 1.5 T.

METHODS

DWI data from a respiratory-gated MRI sequence with b = 0, 50, 250, 800 s/mm² were retrospectively analysed in 173 lesions and 40 healthy livers. The apparent diffusion coefficient ADC = ADC(0,800) and IVIM-based parameters D₁' = ADC(50,800), D₂' =ADC(250,800), f₁', f₂', D*', ADC_low = ADC(0,50), and ADC_diff=ADC_low-D₂' were calculated voxel-wise without fitting procedures. Differences between lesion groups were investigated.

RESULTS

Focal nodular hyperplasias were best discriminated from all other lesions by f₁' with an area under the curve (AUC) of 0.989. Haemangiomas were best discriminated by D₁' (AUC of 0.994). For discrimination between malignant and benign lesions, ADC(0,800) and D₁' were best suited (AUC of 0.915 and 0.858, respectively). Discriminatory power was further increased by using a combination of D₁' and f₁'.

CONCLUSION

IVIM parameters D and f approximated from three b-values provided more discriminatory power between liver lesions than ADC determined from two b-values. The use of b = 0, 50, 800 s/mm² was superior to that of b = 0, 250, 800 s/mm². The acquisition of four instead of three b-values has no further benefit for lesion characterisation.

KEY POINTS

• Diffusion and perfusion characteristics are assessable with only three b-values. • Association of b = 0, 50, 800 s/mm²is superior to b = 0, 250, 800 s/mm². • A fourth acquired b-value has no benefit for differential diagnosis. • For liver lesion characterisation, simplified IVIM analysis is superior to ADC determination. • Simplified IVIM approach guarantees numerically stable, voxel-wise results and short acquisition times.

Whole-Body MRI: Current Applications in Oncology

OBJECTIVE

The purpose of this article is to review current image acquisition and interpretation for whole-body MRI, clinical applications, and the emerging roles in oncologic imaging, especially in the assessment of bone marrow diseases.

CONCLUSION

Whole-body MRI is an emerging technique used for early diagnosis, staging, and assessment of therapeutic response in oncology. The improved accessibility and advances in technology, including widely available sequences (Dixon and DWI), have accelerated its deployment and acceptance in clinical practice.

Diffusion imaging of the vertebral bone marrow

Diffusion-weighted MRI (DWI) of the vertebral bone marrow is a clinically important tool for the characterization of bone-marrow pathologies and, in particular, for the differentiation of benign (osteoporotic) and malignant vertebral compression fractures. DWI of the vertebral bone marrow is, however, complicated by some unique MR and tissue properties of vertebral bone marrow. Due to both the spongy microstructure of the trabecular bone and the proximity of the lungs, soft tissue, or large vessels, substantial magnetic susceptibility variations occur, which severely reduce the magnetic field homogeneity as well as the transverse relaxation time T^*₂ , and thus complicate MRI in particular with echoplanar imaging (EPI) techniques. Therefore, alternative diffusion-weighting pulse sequence types such as single-shot fast-spin-echo sequences or segmented EPI techniques became important alternatives for quantitative DWI of the vertebral bone marrow. This review first describes pulse sequence types that are particularly important for DWI of the vertebral bone marrow. Then, data from 24 studies that made diffusion measurements of normal vertebral bone marrow are reviewed; summarizing all results, the apparent diffusion coefficient (ADC) of normal vertebral bone marrow is typically found to be between 0.2 and 0.6 × 10^-3  mm² /s. Finally, DWI of vertebral compression fractures is discussed. Numerous studies demonstrate significantly greater ADCs in osteoporotic fractures (typically between 1.2 and 2.0 × 10^-3  mm² /s) than in malignant fractures or lesions (typically 0.7-1.3 × 10^-3  mm² /s). Alternatively, several studies used the (qualitative) image contrast of diffusion-weighted acquisitions for differentiation of lesion etiology: a very good lesion differentiation can be achieved, particularly with diffusion-weighted steady-state free precession sequences, which depict malignant lesions as hyperintense relative to normal-appearing vertebral bone marrow, in contrast to hypointense or isointense osteoporotic lesions. Copyright © 2015 John Wiley & Sons, Ltd.

Comparison of 2D single-shot turbo-spin-echo and spin-echo echo-planar diffusion weighted brain MRI at 3.0 Tesla: preliminary experience in children

PURPOSE

To qualitatively compare a 2D single-shot turbo-spin-echo (ssTSE) diffusion-weighted imaging MRI technique with a spin-echo echo-planar imaging (SE-EPI) approach in pediatric neuroimaging.

METHODS

Images were acquired at 3T in 15 patients (10.6±6.0years). A neuroradiologist rated the data based on the severity of image artifacts from air-tissue interfaces and devices such as ventriculoperitoneal shunts and orthodontia, and whether their presence affected diagnostic image quality.

RESULTS

ssTSE was preferred over SE-EPI in diagnostic image quality and exhibited fewer clinically relevant artifacts (p<0.01).

CONCLUSION

ssTSE provides superior diffusion-weighted brain images at 3T, particularly in the presence of orthodontia and shunts.

Use of diffusion-weighted magnetic resonance imaging to distinguish between lung cancer and focal inflammatory lesions: a comparison of intravoxel incoherent motion derived parameters and apparent diffusion coefficient

Background Using imaging techniques to diagnose malignant and inflammatory lesions in the lung can be challenging. Purpose To compare intravoxel incoherent motion (IVIM) and apparent diffusion coefficient (ADC) magnetic resonance imaging (MRI) analysis in their ability to discriminate lung cancer from focal inflammatory lung lesions. Material and Methods Thirty-eight patients with lung masses were included: 30 lung cancers and eight inflammatory lesions. Patients were imaged with 3.0T MRI diffusion weighted imaging (DWI) using 10 b values (range, 0-1000 s/mm²). Tissue diffusivity ( D), pseudo-diffusion coefficient ( D*), and perfusion fraction ( f) were calculated using segmented biexponential analysis. ADC (total) was calculated with monoexponential fitting of the DWI data. D, D*, f, and ADC were compared between lung cancer and inflammatory lung lesions. Receiver operating characteristic analysis was performed for all DWI parameters. Results The ADC was significantly higher for inflammatory lesions than for lung cancer ([1.21 ± 0.20] × 10^-3 mm²/s vs. [0.97 ± 0.15] × 10^-3 mm²/s; P = 0.004). By IVIM, f was found to be significantly higher in inflammatory lesions than lung cancer ([46.10 ± 12.92] % vs. [29.29 ± 10.89] %; P = 0.005). There was no difference in D and D* between lung cancer and inflammatory lesions ( P = 0.747 and 0.124, respectively). f showed comparable diagnostic performance with ADC in differentiating lung cancer from inflammatory lung lesions, with areas under the curve of 0.833 and 0.826, sensitivity 80.0% and 73.3%, and specificity 75.0% and 87.5%, respectively. Conclusion The IVIM parameter f value provides comparable diagnostic performance with ADC and could be used as a surrogate marker for differentiating lung cancer from inflammatory lesions.

Dose-dependent white matter damage after brain radiotherapy

BACKGROUND AND PURPOSE

Brain radiotherapy is limited in part by damage to white matter, contributing to neurocognitive decline. We utilized diffusion tensor imaging (DTI) with multiple b-values (diffusion weightings) to model the dose-dependency and time course of radiation effects on white matter.

MATERIALS AND METHODS

Fifteen patients with high-grade gliomas treated with radiotherapy and chemotherapy underwent MRI with DTI prior to radiotherapy, and after months 1, 4-6, and 9-11. Diffusion tensors were calculated using three weightings (high, standard, and low b-values) and maps of fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (λ∥), and radial diffusivity (λ⊥) were generated. The region of interest was all white matter.

RESULTS

MD, λ∥, and λ⊥ increased significantly with time and dose, with corresponding decrease in FA. Greater changes were seen at lower b-values, except for FA. Time-dose interactions were highly significant at 4-6months and beyond (p<.001), and the difference in dose response between high and low b-values reached statistical significance at 9-11months for MD, λ∥, and λ⊥ (p<.001, p<.001, p=.005 respectively) as well as at 4-6months for λ∥ (p=.04).

CONCLUSIONS

We detected dose-dependent changes across all doses, even <10Gy. Greater changes were observed at low b-values, suggesting prominent extracellular changes possibly due to vascular permeability and neuroinflammation.

Magnetic Resonance Imaging Technique for Visualization of Irregular Cerebrospinal Fluid Motion in the Ventricular System and Subarachnoid Space

BACKGROUND

Many studies have shown that cerebrospinal fluid (CSF) behaves irregularly, rather than with laminar flow, in the various CSF spaces. We adapted a modified previously known magnetic resonance imaging technique to visualize irregular CSF motion. Subsequently, we assessed the usefulness and clinical significance of the present method.

MATERIALS AND METHODS

Normal CSF motion in 10 healthy volunteers was visualized with the dynamic improved, motion-sensitized, driven-equilibrium steady-state free precession technique. Subsequently, CSF motion visualization with a modified sequence was applied to 3 patients.

RESULTS

In healthy volunteers, we achieved visualization of the irregularity of CSF flow in the ventricles and spinal canal, whereas CSF motion was diminished in the peripheral part of the intracranial subarachnoid space. In one case, we confirmed the patency of the patient's third ventriculostomy fenestration site. In the other, we verified the usefulness of the proposed sequence for determining the communication between the ventricle or subarachnoid space and the cyst.

CONCLUSIONS

Using the present sequence, we obtained images that accentuated CSF motion, which is largely composed of irregular motion. This method does not require pulse triggering or complex post-processing of images and allows visualization of CSF motion in a short period of time in selected whole imaging planes. It can therefore be applied clinically to diagnose various diseases that cause abnormalities in the CSF space.

Intravoxel incoherent motion diffusion weighted MRI of cervical cancer - Correlated with tumor differentiation and perfusion

OBJECTIVES

To investigate the value of parameters derived from IVIM model in grading of uterine cervical cancer and the relationship between perfusion parameters derived from IVIM and that from DCE-MRI.

METHODS

Parameters of DWI (ADC, D, f, D*) and semi-quantitative parameters of DCE-MRI (Slop, Maxslop, CER, Washout, AUC90) were assessed in 24 female with cervical cancers. Except for ROIs encompassed all of the area of tumors in axial plane (A_all), ROIs on tumor edge (A_peri) and tumor center (A_central) were drawn. All of the parameters were compared among three pathology grades. Perfusion parameters derived from IVIM were correlated with that from DCE-MRI.

RESULTS

For G1, G2 and G3 tumors, on tumor edge ADC=(1.03±0.11), (1.05±0.10), (0.90±0.05)×10(-3)mm(2)/s, D=(0.80±0.11), (0.78±0.07), (0.69±0.06)×10(-3)mm(2)/s, and f=(0.19±0.03), (0.22±0.02), (0.24±0.03). The differences among groups were significant (P<0.05). On tumor center, ADC=(0.90±0.10), (0.85±0.03), (0.80±0.07)×10(-3)mm(2)/s with significant differences (P=0.027). The other parameter, D and f of tumor center, as well as D* of all tumor areas, were of no statistic significance. Most of the DCE-MRI parameters negatively correlated with tumor volume. Although the correlation between f and slop was statistic significant, R=0.277 meant a negligible correlation. f had week correlation with Maxslop, CER and AUC90 (R=0.361, 0.400 and 0.405; P<0.001). D* showed no statistic significant correlation with all of the DCE parameters.

CONCLUSION

IVIM model could possibly be used to evaluate tumor differentiation and perfusion, providing an alternative for DCE-MRI.

Inter- and Intra-Observer Repeatability of Quantitative Whole-Body, Diffusion-Weighted Imaging (WBDWI) in Metastatic Bone Disease

Quantitative whole-body diffusion-weighted MRI (WB-DWI) is now possible using semi-automatic segmentation techniques. The method enables whole-body estimates of global Apparent Diffusion Coefficient (gADC) and total Diffusion Volume (tDV), both of which have demonstrated considerable utility for assessing treatment response in patients with bone metastases from primary prostate and breast cancers. Here we investigate the agreement (inter-observer repeatability) between two radiologists in their definition of Volumes Of Interest (VOIs) and subsequent assessment of tDV and gADC on an exploratory patient cohort of nine. Furthermore, each radiologist was asked to repeat his or her measurements on the same patient data sets one month later to identify the intra-observer repeatability of the technique. Using a Markov Chain Monte Carlo (MCMC) estimation method provided full posterior probabilities of repeatability measures along with maximum a-posteriori values and 95% confidence intervals. Our estimates of the inter-observer Intraclass Correlation Coefficient (ICCinter) for log-tDV and median gADC were 1.00 (0.97-1.00) and 0.99 (0.89-0.99) respectively, indicating excellent observer agreement for these metrics. Mean gADC values were found to have ICCinter = 0.97 (0.81-0.99) indicating a slight sensitivity to outliers in the derived distributions of gADC. Of the higher order gADC statistics, skewness was demonstrated to have good inter-user agreement with ICCinter = 0.99 (0.86-1.00), whereas gADC variance and kurtosis performed relatively poorly: 0.89 (0.39-0.97) and 0.96 (0.69-0.99) respectively. Estimates of intra-observer repeatability (ICCintra) demonstrated similar results: 0.99 (0.95-1.00) for log-tDV, 0.98 (0.89-0.99) and 0.97 (0.83-0.99) for median and mean gADC respectively, 0.64 (0.25-0.88) for gADC variance, 0.85 (0.57-0.95) for gADC skewness and 0.85 (0.57-0.95) for gADC kurtosis. Further investigation of two anomalous patient cases revealed that a very small proportion of voxels with outlying gADC values lead to instability in higher order gADC statistics. We therefore conclude that estimates of median/mean gADC and tumour volume demonstrate excellent inter- and intra-observer repeatability whilst higher order statistics of gADC should be used with caution when ascribing significance to clinical changes.

Diffusion-Weighted Imaging with Two Different b-Values in Detection of Solid Focal Liver Lesions

One hundred and eighty-two consecutive patients with suspected liver disease were recruited to receive diffusion-weighted imaging (DWI) with two different b-values, in comparison with T2-weighted imaging (T2WI). The detection rate of three MR sequences in solid focal liver lesions (FLLs) and subgroup analyses were performed. Our prospective study found that DWI600 was equivalent to DWI100 and T2WI for the detection of solid FLLs overall but was significantly more accurate in the detection of malignant solid FLLs and lesions larger than 10 mm.

Intravoxel incoherent motion diffusion-weighted imaging in differentiating uterine fibroid from focal adenomyosis: initial results

To evaluate the performance of intravoxel incoherent motion (IVIM)-diffusion-weighted imaging (DWI) in differentiating uterine fibroids from focal adenomyosises. Twenty-five uterine fibroids and 21 focal adenomyosises prospectively underwent IVIM-DWI examination prior to surgery. Four parameters including apparent diffusion coefficient total values (ADCtot), true diffusion coefficient (D), pseudodiffusion coefficient (D*) and perfusion fraction (f) derived from IVIM-DWI images were separately calculated and compared across four groups. There was a statistically significant difference in IVIM-derived f parameter between fibroid and focal adenomyosis (p = 0.01) and control group (p = 0.02). Uterine fibroids gave higher coefficient of variation (CV) of all IVIM-derived parameters than focal adenomyosises. IVIM-DWI could improve the sensitivity and specificity of detecting focal adenomyosis to 100 and 92.6 %, respectively. IVIM-f parameter could be potentially used to better distinguish uterine fibroid from focal adenomyosis. The higher CV of IVIM-derived parameters with acceptable range is often observed in the diseased group.

Is low b-factors-based apparent diffusion coefficient helpful in assessing renal dysfunction?

PURPOSE

To investigate whether low b-factors-based apparent diffusion coefficient (ADC) is helpful in assessing renal dysfunction.

MATERIALS AND METHODS

Forty-four subjects were recruited, and classified as having severe renal injury group (sRI) or not (non-sRI) according to a threshold of estimated glomerular filtration rate (eGFR) = 30 ml/min/1.73 m(2). A free-breathing DWI with 7 b-factors (0, 20, 40, 80, 200, 400, and 800 s/mm(2)) was performed. After choosing an anatomical section that covered the largest part of right kidney, the regions of interest covered the renal parenchyma. For each subject, two apparent diffusion coefficients based on all b-factors less than 400 s/mm(2) (ADC0-400) and 800 s/mm(2) (ADC0-800) were calculated by fitting the signal intensity at different b-factors to a mono-exponential decay, respectively. It was found that the examination time of the free-breathing DWI sequence in this study can be reduced from 3.27 to 2.55 min if the b-factor (800 s/mm(2)) is removed.

RESULTS

ADC0-400 was larger than ADC0-800 in each group (P < 0.05). Both ADC0-400 and ADC0-800 were smaller in the sRI group than those in the non-sRI group (P < 0.01), and they were linearly related with eGFR (P < 0.05). While a significant difference was not found between the two coefficients to differentiate sRI from non-sRI participants (P > 0.05), a strong correlation was present between ADC0-400 and ADC0-800 (r = 0.856, P < 0.001).

CONCLUSION

The low b-factors-based ADC was an economical option for reducing the examination time without sacrificing its diagnostic performance.

MRI methods for the evaluation of high intensity focused ultrasound tumor treatment: Current status and future needs

Thermal ablation with high intensity focused ultrasound (HIFU) is an emerging noninvasive technique for the treatment of solid tumors. HIFU treatment of malignant tumors requires accurate treatment planning, monitoring and evaluation, which can be facilitated by performing the procedure in an MR-guided HIFU system. The MR-based evaluation of HIFU treatment is most often restricted to contrast-enhanced T1 -weighted imaging, while it has been shown that the non-perfused volume may not reflect the extent of nonviable tumor tissue after HIFU treatment. There are multiple studies in which more advanced MRI methods were assessed for their suitability for the evaluation of HIFU treatment. While several of these methods seem promising regarding their sensitivity to HIFU-induced tissue changes, there is still ample room for improvement of MRI protocols for HIFU treatment evaluation. In this review article, we describe the major acute and delayed effects of HIFU treatment. For each effect, the MRI methods that have been-or could be-used to detect the associated tissue changes are described. In addition, the potential value of multiparametric MRI for the evaluation of HIFU treatment is discussed. The review ends with a discussion on future directions for the MRI-based evaluation of HIFU treatment.

Is 3-Tesla Gd-EOB-DTPA-enhanced MRI with diffusion-weighted imaging superior to 64-slice contrast-enhanced CT for the diagnosis of hepatocellular carcinoma?

Objectives

To compare 64-slice contrast-enhanced computed tomography (CT) with 3-Tesla magnetic resonance imaging (MRI) using Gd-EOB-DTPA for the diagnosis of hepatocellular carcinoma (HCC) and evaluate the utility of diffusion-weighted imaging (DWI) in this setting.

Methods

3-phase-liver-CT was performed in fifty patients (42 male, 8 female) with suspected or proven HCC. The patients were subjected to a 3-Tesla-MRI-examination with Gd-EOB-DTPA and diffusion weighted imaging (DWI) at b-values of 0, 50 and 400 s/mm². The apparent diffusion coefficient (ADC)-value was determined for each lesion detected in DWI. The histopathological report after resection or biopsy of a lesion served as the gold standard, and a surrogate of follow-up or complementary imaging techniques in combination with clinical and paraclinical parameters was used in unresected lesions. Diagnostic accuracy, sensitivity, specificity, and positive and negative predictive values were evaluated for each technique.

Results

MRI detected slightly more lesions that were considered suspicious for HCC per patient compared to CT (2.7 versus 2.3, respectively). ADC-measurements in HCC showed notably heterogeneous values with a median of 1.2±0.5×10⁻³ mm²/s (range from 0.07±0.1 to 3.0±0.1×10⁻³ mm²/s). MRI showed similar diagnostic accuracy, sensitivity, and positive and negative predictive values compared to CT (AUC 0.837, sensitivity 92%, PPV 80% and NPV 90% for MRI vs. AUC 0.798, sensitivity 85%, PPV 79% and NPV 82% for CT; not significant). Specificity was 75% for both techniques.

Conclusions

Our study did not show a statistically significant difference in detection in detection of HCC between MRI and CT. Gd-EOB-DTPA-enhanced MRI tended to detect more lesions per patient compared to contrast-enhanced CT; therefore, we would recommend this modality as the first-choice imaging method for the detection of HCC and therapeutic decisions. However, contrast-enhanced CT was not inferior in our study, so that it can be a useful image modality for follow-up examinations.

Microvascular invasion in small hepatocellular carcinoma: is it predictable with preoperative diffusion-weighted imaging?

BACKGROUND AND AIM

The presence of microvascular invasion (MVI) is an independent risk factor affecting recurrence-free survival following surgical treatment for small hepatocellular carcinoma (HCC). Our aim in this study was to investigate whether diffusion-weighted imaging (DWI) could be useful in predicting MVI for small HCC.

METHODS

Breath-hold DWI (b-value 0, 500 s/mm(2) ) and gadopentate dimeglumine-enhanced dynamic imaging of preoperative magnetic resonance imaging of 109 surgically proven small HCCs from 92 patients were retrospectively analyzed. The signal intensity ratio on DWI and apparent diffusion coefficients (ADCs) for lesions were quantitatively measured. Signal intensity ratio and ADC of DWI, tumor size, tumor shape, tumor capsule, peritumoral enhancement on arterial phase images, and dynamic enhancement pattern were analyzed as radiological parameters reflecting MVI and were compared with histopathological references. The chi-square test, Fisher's exact test, Mann-Whitney U test, and the independent t-test were used for univariate analysis. To identify the independent predictors of MVI among these radiological parameters and to evaluate their diagnostic performance, multivariate logistic regression analysis and receiver operating characteristic curve analysis were performed, respectively.

RESULTS

A univariate analysis showed that a lower ADC value (P = 0.005) and irregular circumferential enhancement (P = 0.020) showed statistically significant associations with MVI. A multiple logistic regression analysis showed that the ADC value and irregular circumferential enhancement were independent predictors of MVI. With a cut-off of 1.227 × 10(-3)  mm(2) /s, the ADC value provided a sensitivity of 66.7% and a specificity of 78.6% in the prediction of MVI with an odds ratio of 7.63 (P < 0.01).

CONCLUSIONS

Lower ADC values (< 1.227 × 10(-3)  mm(2) /s) on DWI with b-value of 0.500 s/mm(2) can be a useful preoperative predictor of MVI for small HCCs.

Nasopharyngeal carcinoma: comparison of diffusion and perfusion characteristics between different tumour stages using intravoxel incoherent motion MR imaging

OBJECTIVE

To explore intravoxel incoherent motion (IVIM) characteristics of nasopharyngeal carcinoma (NPC) and relationships with different tumour stages.

METHODS

We prospectively recruited 80 patients with newly diagnosed undifferentiated NPC. Diffusion-weighted MR imaging was performed and IVIM parameters (D, pure diffusion; f, perfusion fraction; D*, pseudodiffusion coefficient) were calculated. Patients were stratified into low and high tumour stage groups based on American Joint Committee on Cancer (AJCC) and TNM staging for determination of the predictive powers of IVIM parameters using t test, multiple logistic regression and ROC curve analyses.

RESULTS

D, f and D* were all statistically significantly lower in high-stage groups in AJCC, T and N staging. D, f and D* were all independent predictors of AJCC staging, f and D* were independent predictors of T staging, and D was an independent predictor of N staging. D was most powerful for AJCC and N staging, whereas f was most powerful for T staging. Optimal cut-off values (area under the curve, sensitivity, specificity, positive likelihood ratio, negative likelihood ratio) were as follows: AJCC stage, D = 0.782 × 10(-3) mm(2)/s (0.915, 93.3 %, 76.2 %, 3.92, 0.09); T staging, f = 0.133 (0.905, 80.5 %, 92.5 %, 10.73, 0.21); N staging, D = 0.761 × 10(-3) mm(2)/s (0.848, 87.5 %, 66.7 %, 2.62, 0.19). Multivariate analysis showed no diagnostic improvement.

CONCLUSION

Nasopharyngeal carcinoma has distinctive intravoxel incoherent motion characteristics parameters in different tumour staging, potentially helping pretreatment staging.

KEY POINTS

• Magnetic resonance imaging is increasingly used to assess nasopharyngeal carcinoma (NPC). • NPC has distinctive diffusion/perfusion characteristics at different stages. • Non-invasive MR imaging may help pretreatment staging prediction. • Diffusion properties of NPC best correlate with AJCC and N staging. • Perfusion properties of NPC best correlate with T staging.

Separate calculation of DW-MRI in assessing therapeutic effect in liver tumors in rats

AIM: To explore whether the antitumor effect of a vascular disrupting agent (VDA) would be enhanced by combining with an antiangiogenic agent, and whether such synergistic effects can be effectively evaluated with separate calculation of diffusion weighted magnetic resonance imaging (DW-MRI).

METHODS: Thirty-seven rats with implanted liver tumors were randomized into the following three groups: (1) ZD6126, a kind of VDA; (2) ZDTHA, ZD6126 in combination with an antiangiogenic, thalidomide; and (3) control. Morphological DW-MRI were performed and quantified before, 4 h and 2 d after treatment. The apparent diffusion coefficient (ADC) values were calculated separately for low b values (ADC_low), high b values (ADC_high) and all b values (ADC_all). The tissue perfusion contribution, ADC_perf, was calculated as ADC_low-ADC_high. Imaging findings were finally verified by histopathology.

RESULTS: The combination therapy with ZDTHA significantly delayed tumor growth due to synergistic effects by inducing cumulative tumor necrosis. In addition to delaying tumor growth, ZDTHA caused tumor necrosis in an additive manner, which was verified by HE staining. Although both ADC_high and ADC_all in the ZD6126 and ZDTHA groups were significantly higher compared to those in the control group on day 2, the entire tumor ADC_high of ZDTHA was even higher than that of ZD6126, but the significant difference was not observed for ADC_all between ZDTHA and ZD6126. This indicated that the perfusion insensitive ADC_high values calculated from high b value images performed significantly better than ADC_all for the monitoring of tumor necrosis on day 2. The perfusion sensitive ADC_perf derived from ADC_low by excluding high b value effects could better reflect the reduction of blood flow due to the vessel shutdown induced by ZD6126, compared to the ADC_low at 4 h. The ADC_perf could provide valuable perfusion information from DW-MRI data.

CONCLUSION: The separate calculation of ADC is more useful than conventional averaged ADC in evaluating the efficacy of combination therapy with ZD6126 and thalidomide for solid tumors.

Nonalcoholic fatty liver disease: intravoxel incoherent motion diffusion-weighted MR imaging-an experimental study in a rabbit model

PURPOSE

To evaluate the feasibility of using intravoxel incoherent motion (IVIM) diffusion-weighted imaging with multiple b values for the noninvasive diagnosis of nonalcoholic fatty liver disease (NAFLD).

MATERIALS AND METHODS

This study was approved by the institutional animal care and use committee. Twenty-seven 8-week-old rabbits were fed a variety of diets (from a standard diet to a high-fat, high-cholesterol diet) before IVIM diffusion-weighted imaging was performed with seven b values by using a 3-T magnetic resonance (MR) imaging unit. At histologic analysis of the animals, livers were categorized by NAFLD severity as normal, NAFLD, borderline nonalcoholic steatohepatitis (NASH), or NASH. The apparent diffusion coefficient and IVIM-derived parameters including true diffusion coefficient, pseudodiffusion coefficient, and perfusion fraction of the liver parenchyma were measured. Each parameter was correlated with NAFLD severity, and optimal cutoff values were determined by means of receiver operating characteristics analysis.

RESULTS

Perfusion fraction was significantly lower in rabbits with NAFLD than in those with a normal liver, and it decreased further as severity of NAFLD increased, with medians of 22.2%, 14.8%, 11.3%, and 9.5% in the rabbits in the normal, NAFLD, borderline, and NASH groups, respectively (ρ = -0.83, P < .001). Apparent diffusion coefficient, true diffusion coefficient, and pseudodiffusion coefficient were not significantly different between the NAFLD severity groups. In terms of the diagnostic performance of perfusion fraction, area under the curve values were 0.984 (normal vs NAFLD or more severe disease), 0.959 (NAFLD or less severe vs borderline or more severe disease), and 0.903 (borderline or less severe vs NASH) with optimal cutoff values of 15.2%, 13.2%, and 11.0%, respectively.

CONCLUSION

Perfusion fractions extracted from IVIM diffusion-weighted imaging may help in the differentiation of early stage NASH from simple steatosis.

Nonalcoholic Fatty Liver Disease: Intravoxel Incoherent Motion Diffusion-weighted MR Imaging-An Experimental Study in a Rabbit Model

Purpose To evaluate the feasibility of using intravoxel incoherent motion (IVIM) diffusion-weighted imaging with multiple b values for the noninvasive diagnosis of nonalcoholic fatty liver disease (NAFLD). Materials and Methods This study was approved by the institutional animal care and use committee. Twenty-seven 8-week-old rabbits were fed a variety of diets (from a standard diet to a high-fat, high-cholesterol diet) before IVIM diffusion-weighted imaging was performed with seven b values by using a 3-T magnetic resonance (MR) imaging unit. At histologic analysis of the animals, livers were categorized by NAFLD severity as normal, NAFLD, borderline nonalcoholic steatohepatitis (NASH), or NASH. The apparent diffusion coefficient and IVIM-derived parameters including true diffusion coefficient, pseudodiffusion coefficient, and perfusion fraction of the liver parenchyma were measured. Each parameter was correlated with NAFLD severity, and optimal cutoff values were determined by means of receiver operating characteristics analysis. Results Perfusion fraction was significantly lower in rabbits with NAFLD than in those with a normal liver, and it decreased further as severity of NAFLD increased, with medians of 22.2%, 14.8%, 11.3%, and 9.5% in the rabbits in the normal, NAFLD, borderline, and NASH groups, respectively (ρ = -0.83, P < .001). Apparent diffusion coefficient, true diffusion coefficient, and pseudodiffusion coefficient were not significantly different between the NAFLD severity groups. In terms of the diagnostic performance of perfusion fraction, area under the curve values were 0.984 (normal vs NAFLD or more severe disease), 0.959 (NAFLD or less severe vs borderline or more severe disease), and 0.903 (borderline or less severe vs NASH) with optimal cutoff values of 15.2%, 13.2%, and 11.0%, respectively. Conclusion Perfusion fractions extracted from IVIM diffusion-weighted imaging may help in the differentiation of early stage NASH from simple steatosis. © RSNA, 2013.

[Usefulness of short inversion time inversion recovery-low B diffusion weighted imaging after pouring in gadolinium- ethoxybenzyl-diethylene-triaminepentaacetic acid]

Diffusion weighted imaging (DWI) using a low b value for examination of the body is not common, so we examined its usefulness. Phantom experiments were performed in which I changed the length of the echo time (TE), with and without short inversion time inversion recovery (STIR). The signal intensity of each phantom was reduced by using a longer TE or by combination with STIR, but contrast was improved. We noted a similar pattern in clinical cases, and concluded that the results of the phantom study and clinical cases indicated the potential usefulness of TE with moderate STIR. Low-b DWI using appropriate imaging parameters gave better results than high-b DWI followed by visual assessment. The T1 value of normal liver cells is shortened by incorporating gadolinium-ethoxybenzyl-diethylene-triaminepentaacetic acid (Gd-EOB-DTPA). Normal liver cells are close to the null point in STIR-low-b DWI under these conditions. The signal-to-noise ratio (SNR) of normal liver cells thus decreases, unlike that for tumors containing no normal liver cells, giving improved contrast. At high SNRs, the use of low-b DWI provides several advantages: the anatomical location structure is easy to identify, and there is less left lateral division of liver signal degradation. We thus conclude STIR-low-b DWI after injection of Gd-EOB-DTPA to be a useful technique.

Intravoxel incoherent motion model-based liver lesion characterisation from three b-value diffusion-weighted MRI

OBJECTIVE

To evaluate intravoxel incoherent motion (IVIM) model-based liver lesion characterisation from three b-value diffusion-weighted imaging (DWI).

METHODS

The 1.5-T DWI data from a respiratory gated spin-echo echo-planar magnetic resonance imaging sequence (b = 0, 50, 800 s/mm(2)) were retrospectively analysed in 38 patients with different liver lesions. Conventional apparent diffusion coefficient ADC = ADC(0,800) as well as IVIM-based parameters D' = ADC(50,800), ADC_low = ADC(0,50), and f' were calculated voxel-wise. Sixty-one regions of interest in hepatocellular carcinomas (HCCs, n = 24), haemangiomas (HEMs, n = 11), focal nodular hyperplasias (FNHs, n = 11), and healthy liver tissue (REFs, n = 15) were analysed. Group differences were investigated using Student's t-test and receiver-operating characteristic (ROC) analysis.

RESULTS

Mean values ± standard deviations of ADC, D', ADC_low (in 10(-5) mm(2)/s), and f' (in %) for REFs/FNHs/HEMs/HCCs were 130 ± 11/143 ± 27/168 ± 16/113 ± 25, 104 ± 12/123 ± 25/162 ± 18/102 ± 23, 518 ± 66/437 ± 97/268 ± 69/283 ± 120, and 18 ± 3/14 ± 4/6 ± 3/9 ± 5, respectively. Differences between lesions and REFs were more significant for IVIM-based parameters than for conventional ADC. ROC analysis showed the best discriminability between HCCs and FNHs for ADC_low and f' and between HEMs and FNHs or HCCs for D'.

CONCLUSION

Three instead of two b-value DWI enables a numerically stable and voxel-wise IVIM-based analysis for improved liver lesion characterisation with tolerable acquisition time.

KEY POINTS

• Quantitative analysis of diffusion-weighted MRI helps liver lesion characterisation. • Analysis of intravoxel incoherent motion is superior to apparent diffusion coefficient determination. • Only three b-values enable separation of diffusion and microcirculation effects. • The method presented is numerically stable, with voxel-wise results and short acquisition times.