Body and Cardiovascular MR Imaging at 3.0 T

Comparison of single-shot EPI and multi-shot EPI in prostate DWI at 3.0 T

In prostate MRI, single-shot EPI (ssEPI) DWI still suffers from distortion and blurring. Multi-shot EPI (msEPI) overcomes the drawbacks of ssEPI DWI. The aim of this article was to compare the image quality and diagnostic performance for clinically significant prostate cancer (csPC) between ssEPI DWI and msEPI DWI. This retrospective study included 134 patients with suspected PC who underwent 3.0 T MRI and subsequent MRI-guided biopsy. Three radiologists independently assessed anatomical distortion, prostate edge clarity, and lesion conspicuity score for pathologically confirmed csPC. Lesion apparent diffusion coefficient (ADC) and benign ADC were also calculated. In 17 PC patients who underwent prostatectomy, three radiologists independently assessed eight prostate regions by DWI score in PI-RADS v 2.1. Anatomical distortion and prostate edge clarity were significantly higher in msEPI DWI than in ssEPI DWI in the three readers. Lesion conspicuity score was significantly higher in msEPI DWI than in ssEPI DWI in reader 1 and reader 3. Regarding discrimination ability between PC with GS ≤ 3 + 4 and PC with GS ≥ 4 + 3 using lesion ADC, AUC was comparable between ssEPI DWI and msEPI DWI. For diagnostic performance of csPC using DWI score, AUC was comparable between msEPI DWI and ssEPI DWI in all readers. Compared with ssEPI DWI, msEPI DWI had improved image quality and similar or higher diagnostic performance.

Compact pediatric cardiac magnetic resonance imaging protocols

Cardiac MRI is in many respects an ideal modality for pediatric cardiovascular imaging, enabling a complete noninvasive assessment of anatomy, morphology, function and flow in one radiation-free and potentially non-contrast exam. Nonetheless, traditionally lengthy and complex imaging acquisition strategies have often limited its broader use beyond specialized centers. In this review, the author presents practical cardiac MRI imaging protocols to facilitate the performance of succinct yet successful exams that provide the most salient clinical data for the majority of congenital and acquired pediatric cardiac disease. In addition, the author reviews newer and evolving techniques that permit more rapid but similarly diagnostic MRI, including compressed sensing and artificial intelligence/machine learning reconstruction, four-dimensional flow acquisition and blood pool contrast agents. With the modern armamentarium of cardiac MRI methods, the goal of compact yet comprehensive exams in children can now be realized.

Diffusion-weighted imaging in prostate cancer

Diffusion-weighted imaging (DWI), a key component in multiparametric MRI (mpMRI), is useful for tumor detection and localization in clinically significant prostate cancer (csPCa). The Prostate Imaging Reporting and Data System versions 2 and 2.1 (PI-RADS v2 and PI-RADS v2.1) emphasize the role of DWI in determining PIRADS Assessment Category in each of the transition and peripheral zones. In addition, several recent studies have demonstrated comparable performance of abbreviated biparametric MRI (bpMRI), which incorporates only T2-weighted imaging and DWI, compared with mpMRI with dynamic contrast-enhanced MRI. Therefore, further optimization of DWI is essential to achieve clinical application of bpMRI for efficient detection of csPC in patients with elevated PSA levels. Although DWI acquisition is routinely performed using single-shot echo-planar imaging, this method suffers from such as susceptibility artifact and anatomic distortion, which remain to be solved. In this review article, we will outline existing problems in standard DWI using the single-shot echo-planar imaging sequence; discuss solutions that employ newly developed imaging techniques, state-of-the-art technologies, and sequences in DWI; and evaluate the current status of quantitative DWI for assessment of tumor aggressiveness in PC.

Value of bowel preparation techniques for prostate MRI: a preliminary study

Background

Bowel preparation before multiparametric MRI (mpMRI) of the prostate is performed widely, despite contradictory or no evidence for efficacy.

Purpose

To investigate the value of hyoscine N-butylbromide (HBB), microenema (ME) and ‘dietary restrictions’ (DR) for artifact reduction and image quality (IQ) in mpMRI of the prostate.

Study type

Retrospective.

Population

Between 10/2018 and 02/2020 treatment-naïve men (median age, 64.9; range 39.8–87.3) who underwent mpMRI of the prostate were included. The total patient sample comprised of n = 180 patients, who received either HBB, ME, were instructed to adhere to DR, or received a combination of those measures prior to the MR scan.

Field strength/sequence

T2-weighted imaging (T2w), diffusion-weighted imaging (DWI), and dynamic contrast-enhanced MRI (DCE-MRI) scanned on two 3T systems.

Assessment

A radiologist specialized in urogenital imaging (R1) and a senior radiology resident (R2) visually assessed IQ parameters on transversal T2w, DWI and ADC maps on a 5-point Likert-like scale.

Statistical tests

Group comparison between IQ parameters was performed on reader level using Kruskal–Wallis and Mann–Whitney U tests. Binary univariate logistic regression analysis was used to assess independent predictors of IQ. Interrater agreement was assessed using Intraclass Correlation Coefficient (ICC).

Results

‘DWI geometric distortion’ was significantly more pronounced in the HBB+/ME−/DR− (R1, 3.6 and R2, 4.0) as compared to the HBB−/ME+/DR− (R1, 4.2 and R2, 4.6) and HBB+/ME+/DR− (R1, 4.3 and R2, 4.7) cohort, respectively. Parameters ‘DWI IQ’ and ‘Whole MRI IQ’ were rated similarly by both readers. ME was a significant independent predictor of ‘good IQ’ for the whole MRI for R1 [b = 1.09, OR 2.98 (95% CI 1.29, 6.87)] and R2 [b = 1.01, OR 2.73 (95% CI 1.24, 6.04)], respectively.

Data conclusion

ME seems to significantly improve image quality of DWI and the whole mpMRI image set of the prostate. HBB and DR did not have any benefit.

Noncontrast Magnetic Resonance Angiography in the Era of Nephrogenic Systemic Fibrosis and Gadolinium Deposition

ABSTRACT

Gadolinium-based contrast agents for clinical magnetic resonance imaging are overall safe. However, the discovery of nephrogenic systemic fibrosis in patients with severe renal impairment and gadolinium deposition in patients receiving contrast have generated developments in contrast-free imaging of the vasculature, that is, noncontrast magnetic resonance angiography. This article presents an update on noncontrast magnetic resonance angiography techniques, with comparison to other imaging alternatives. Potential benefits and challenges to implementation, and evidence to date for various clinical applications are discussed.

Comparison of reduced field-of-view diffusion-weighted imaging (DWI) and conventional DWI techniques in the assessment of Cervical carcinoma at 3.0T: Image quality and FIGO staging

OBJECTIVE

To evaluate imaging quality (IQ) and International Federation of Gynecology and Obstetrics (FIGO) staging of reduced field-of-view (r-FOV) diffusion-weighted imaging (DWI) in cervical carcinoma (CC).

MATERIALS AND METHODS

Sixty patients with pathologically proven CC who underwent both pre-treatment r-FOV DWI and full field-of-view (f-FOV) DWI on a 3.0T MRI scanner were retrospectively reviewed. The subjective qualitative image scores were compared using the Wilcoxon signed-rank test. Objective quality values and apparent diffusion coefficient (ADC) were estimated by paired t-test or Wilcoxon signed-rank test for the two DWI sequences according to Normality test. Spearman rank correlation analysis was used to evaluate the relationship between pathological results and mean ADC value.

RESULTS

The subjective IQ scores for r-FOV DWI were significantly higher than those for f-FOV DWI (P < 0.001). Similarly, the contrast-to-noise (CNR) value of r-FOV DWI was superior to that of f-FOV DWI (10.30 ± 3.676, 8.91 ± 3.008, P = 0.021). However, the signal-to-noise ratio (SNR) value of r-FOV DWI was considerably lower than that of f-FOV DWI (27.80 ± 6.056, 33.67 ± 7.833, P＜0.001). No significant difference was found between mean ADC values of f-FOV DWI and r-FOV DWI. There was a significant tendency for a negative correlation between the ADC values and FIGO stages of CC for both two sequences (r=-0. 436, P＜0.01; r=-0.470, P＜0.01, respectively).

CONCLUSIONS

The rFOV DWI sequence provided significantly better IQ and lesion conspicuity than the fFOV DWI sequence. In addition, rFOV sequences can be used in evaluation of FIGO staging of cervical cancer.

Liver fibrosis staging with diffusion-weighted imaging: a systematic review and meta-analysis

PURPOSE

A meta-analysis was performed to assess the diagnostic performance of diffusion-weighted imaging (DWI) in liver fibrosis (LF) staging.

METHODS

We conducted a comprehensive literature search to identify relevant articles. Diagnostic data were extracted for each METAVIR fibrosis stage (F0-F4). A bivariate binomial model was used to combine sensitivities and specificities. Summary receiver operating characteristics (SROC) curves were performed and areas under SROC curve (AUC) were calculated to indicate diagnostic accuracies. Subgroup analyses were performed between different study characteristics.

RESULTS

Twelve studies met the inclusion criteria for LF ≥F1, 16 for ≥F2, 18 for ≥F3, and 12 for F4. AUCs of DWI were 0.8554, 0.8770, 0.8836, and 0.8596 for ≥F1, ≥F2, ≥F3, and F4, respectively. Subgroup analyses showed that for LF ≥F2 and ≥F3, maximal b values (b _max) ≥ 800 s/mm² performed significantly better than b _max < 800 s/mm². The diagnostic accuracies of 3.0 T and intravoxel incoherent motion (IVIM)-DWI were significantly higher than those of 1.5 T and conventional DWI for diagnosing liver cirrhosis (F4).

CONCLUSIONS

DWI is a reliable noninvasive technique with good diagnostic accuracy for LF staging. Using b _max ≥ 800 s/mm², high-field strength (3.0 T) and IVIM-DWI can optimize the diagnostic performance of DWI.

Improvement in B1+ Homogeneity and Average Flip Angle Using Dual-Source Parallel RF Excitation for Cardiac MRI in Swine Hearts

Cardiac MRI may benefit from increased polarization at high magnetic field strength of 3 Tesla but is challenged by increased field inhomogeneity. Initial human studies have shown that the radiofrequency (RF) excitation field (B₁⁺) used for signal excitation in the heart is both inhomogeneous and significantly lower than desired, potentially leading to image artifacts and biased quantitative measures. Recently, multi-channel transmit systems have been introduced allowing localized patient specific RF shimming based on acquired calibration B₁⁺ maps. Some prior human studies have shown lower than desired mean flip angles in the hearts of large patients even after RF shimming. Here, 100 cardiac B₁⁺ map pairs before and after RF shimming were acquired in 55 swine. The mean flip angle and the coefficient of variation (CV) of the flip angle in the heart were determined before and after RF shimming. Mean flip angle, CV, and RF shim values (power ratio and phase difference between the two transmit channels) were tested for correlation with cross sectional body area and the Right-Left/Anterior-Posterior ratio. RF shimming significantly increased the mean flip angle in swine heart from 74.4±6.7% (mean ± standard deviation) to 94.7±4.8% of the desired flip angle and significantly reduced CV from 0.11±0.03 to 0.07±0.02 (p<<1e-10 for both). These results compare well with several previous human studies, except that the mean flip angle in the human heart only improved to 89% with RF shimming, possibly because the RF shimming routine does not consider safety constraints in very large patients. Additionally, mean flip angle decreased and CV increased with larger cross sectional body area, however, the RF shimming parameters did not correlate with cross sectional body area. RF shim power ratio correlated weakly with Right-Left/Anterior-Posterior ratio but phase difference did not, further substantiating the need for subject specific cardiac RF shimming.

The presurgical T staging of non-small cell lung cancer: efficacy comparison of 64-MDCT and 3.0 T MRI

Background

Lung cancer has been the main concern of the cancer-related deaths worldwide. Non-small cell lung cancer (NSCLC) is reported the most common subtype of lung cancer. Initial staging of NSCLC is highly associated with the choice of treatment and prognosis of the patients. This study aims to prospectively compare the diagnostic efficacies of 64-multidetector-row computed tomography (MDCT) and 3.0 T magnetic resonance imaging (MRI) in T staging of NSCLC. 

Methods

Institutional review board approval and informed consent were obtained. Forty-five patients diagnosed with NSCLC who underwent preoperative MRI and MDCT scans were enrolled in the study. The efficacies of determination of T staging on MRI and MDCT were compared by using the McNemar test.

Results

Of 45 patients diagnosed with NSCLC, the primary tumors were correctly staged in 38 (84.4 %) patients on MDCT, and in 37 (82.2 %) patients on MRI. There was no statistically significant difference between the two modalities in the overall T staging of NSCLC with the reference of pathological findings (p = 0.564). However, MDCT was indicated more accurate in determination of NSCLC staged T1 and T2 (100 % vs 75 %, 96.4 % vs 82.1 %), whereas MRI was presented slightly superior in identification of NSCLC staged T3 and T4 (80 % vs 50 %, 100 % vs 33.3 %).

Conclusion

Both MDCT and MRI provided acceptable overall accuracies in determination of T staging in NSCLC. Furthermore, MRI was presented slight superiority for the advanced-stage tumors (i.e., NSCLC staged T3 and T4), whereas MDCT was indicated mild acceptance for the limited-stage tumors (i.e., NSCLC staged T1 and T2).

MR Angiography at 3 T of Peripheral Arterial Disease: A Randomized Prospective Comparison of Gadoterate Meglumine and Gadobutrol

OBJECTIVE

This large-scale randomized study aimed to show the noninferiority in terms of diagnostic performance of gadoterate meglumine-enhanced versus gadobutrol-enhanced 3-T MR angiography (MRA) using digital subtraction angiography (DSA) as the reference standard in patients with peripheral arterial occlusive disease (PAOD).

SUBJECTS AND METHODS

In this prospective international randomized double-blind phase IV trial, 189 patients were enrolled. Of them, 156 could be included in the per-protocol population for on-site assessments and 154 for off-site readings. Subjects underwent peripheral MRA, after injection of 0.1 mmol/kg of either gadoterate meglumine or gadobutrol, and DSA within 30 days. The diagnostic accuracy was evaluated and compared using a noninferiority analysis. Secondary endpoints included sensitivity, specificity, diagnostic confidence, contrast-to-noise ratio, and signal-to-noise ratio evaluations.

RESULTS

The percentage agreement between MRA and DSA for stenosis detection was similar for on-site readings for both groups (mean ± SD, 80.6% ± 16.1% with gadoterate meglumine vs 77.1% ± 19.6% with gadobutrol; 3.5% difference), and the same was true for off-site readings (73.9% ± 16.9% with gadoterate meglumine vs 75.1% ± 13.8% with gadobutrol; 1.1% difference). The noninferiority of gadoterate meglumine to gadobutrol was shown for both on- and off-site readings. Sensitivity in detecting significant stenosis (> 50%) was 72.3% for gadoterate meglumine versus 70.6% for gadobutrol, whereas specificity (92.6% vs 92.3%), diagnostic confidence (87.0% vs 86.0%), signal-to-noise ratio (165.5 vs 161.0), and contrast-to-noise ratio (159.5 vs 155.3) did not differ statistically significantly between the two groups.

CONCLUSION

Gadoterate meglumine was found to be not inferior to gadobutrol in terms of diagnostic performance in patients with PAOD undergoing 3-T contrast-enhanced MRA. No statistically significant differences were detected between the two MRA groups.

Clinical Significance of Late Enhancement and Regional Wall Remodeling Assessed by 3T Magnetic Resonance Imaging

BACKGROUND

Clinical follow-up studies comparing left ventricular (LV) function and late gadolinium enhancement (LGE) by high-field 3T cardiac magnetic resonance (CMR) are of general interest due to the increased use of 3T scanners. In this study, the occurrence of LGE and LV regional wall remodeling (RWR) was assessed by 3T CMR in patients undergoing coronary angiography for suspected stable coronary artery disease (CAD).

MATERIALS AND METHODS

Analysis of myocardial viability by LGE was performed at the segmental level. LVRWR was identified by a significant reduction (≥50%) of the wall thickness. Major adverse cardiovascular events (MACE) were registered during a median follow-up time of 58 (45-62) months.

RESULTS

Of the 87 patients (59 ± 9 years; 13 women) enrolled, nonviable myocardium was detected in 35 (40%) and significant CAD in 69 (79%). Nonviable myocardium was correlated to angiographic significant stenosis or occlusion. LVRWR was significantly related to a higher number of nonviable segments compared to those without LVRWR: ie, 6.0 ± 3.2 segments versus 2.6 ± 1.3; P < 0.001. In the nonviable group, LVEF was significantly reduced (P < 0.001) compared to the viable group: ie, 50 ± 16% versus 61 ± 8%, and LVEF was significantly correlated to the number of nonviable segments (r = -0.66, P < 0.001). The number of nonviable segments by LGE was significantly associated with MACE by an odds ratio of 1.25 (95% CI, 1.05-1.49; P = 0.013).

CONCLUSION

The presence of nonviable myocardium as detected by LGE at 3T CMR is associated with angiographically significant CAD, and is associated with the development of LVRWR and reduced LVEF. Assessing the extent of nonviable myocardium by both LGE and LVRWR at the segmental level may therefore contribute to individualized risk stratification and treatment strategies.

Clinical applications of dual-channel transmit MRI: A review

This article reviews the principle of dual-channel transmit MRI and highlights current clinical applications which are performed primarily at 3 Tesla. The main benefits of dual-channel transmit compared with single-transmit systems are the increased image contrast homogeneity and the decreased scanning time due to the more accurate local specific absorption ratio estimation, meaning that less conservative safety limits are needed. The dual-transmit approach has been particularly beneficial in body imaging applications, and is also promising in terms of cardiac, spine, and fetal imaging. Future advances in transmit SENSE, the combination of dual-channel transmit with high permittivity pads, as well as the potential increase in the number of transmit channels are also discussed.

Hidradenitis suppurativa: MRI features in anogenital disease

BACKGROUND

Hidradenitis suppurativa is a rare chronic inflammatory disorder of apocrine gland-bearing skin, which commonly affects the anogenital region. There has been very little literature to date on the MRI appearances of anogenital hidradenitis suppurativa.

OBJECTIVE

The aim of this study was to assess the MRI features of anogenital hidradenitis suppurativa in the largest cohort of patients to be published to date.

DESIGN

After an institutional review board waiver, patients with hidradenitis suppurativa who were undergoing MRI for anogenital disease between 2005 and 2012 were identified from our institutional database. The MRI appearances were recorded by 2 radiologists in consensus, blinded to clinical details. Location of disease, number of tracts, presence of anal fistula, and supralevator involvement were recorded. Patient demographics were also noted.

SETTINGS

This study was conducted at the Department of Radiology, Guy's and St Thomas' National Health Service Foundation Trust.

PATIENTS

Patients included were those undergoing MRI for anogenital disease in hidradenitis suppurativa between 2005 and 2012.

MAIN OUTCOME MEASURES

The distribution of sinus tracts in anogenital hidradenitis suppurativa on MRI was measured.

RESULTS

Thirty-one MRIs were performed in 18 patients (15 men; mean age, 46 years). On the baseline MRI, multiple tracts were seen in the natal cleft (16/18; 83%), the perianal (12/18; 61%), the perineal (13/18; 56%), and the gluteal (8/18; 44%) regions. A communication with the anal canal was present in only 4 patients. Three patients had supralevator extension. Seven patients had follow-up MRIs with variable response to interval treatment: 3 of 7 showed responding disease, 3 of 7 showed stable disease, and 1 of 7 showed progressive disease.

LIMITATIONS

This study was limited by its relatively small cohort of patients.

CONCLUSIONS

In hidradenitis suppurativa, anogenital disease is usually subcutaneous but extensive, with only a minority of patients demonstrating deeper involvement. MRI may help define the extent of anogenital disease and assess response to treatment.

Prospective comparison of 3T MRI with diffusion-weighted imaging and MDCT for the preoperative TNM staging of gastric cancer

PURPOSE

To compare the diagnostic performance of 3T magnetic resonance imaging (MRI) with diffusion-weighted imaging (DWI) and multidetector-row computed tomography (MDCT) for the preoperative TNM staging of gastric cancer.

MATERIALS AND METHODS

This prospective study was approved by our Institutional Review Board. Forty-nine consecutive patients with histologically confirmed gastric cancers underwent MDCT and 3T MRI followed by surgery. MRI without DWI, MRI with DWI, and MDCT were reviewed to determine preoperative TNM staging. Using the pathologic stages as the reference standard, the diagnostic performance of each imaging modality was compared.

RESULTS

Diagnostic accuracies of MRI with DWI, MRI without DWI, and MDCT did not show a significant difference (≤T2 vs. ≥T3: 85.1%, 78.7%, and 80.9%; ≤T3 vs. T4: 76.6%, 74.5%, and 72.3%; N-negative vs. N-positive: 76.6%, 66.0%, and 63.8%; M0 vs. M1: all 95.9%, respectively) (P > 0.05). For N staging, MRI with DWI demonstrated higher sensitivity but lower specificity (86.7% and 58.8%, respectively) than MRI without DWI (50.0% and 94.1%) or MDCT (43.3% and 100%) (P < 0.05).

CONCLUSION

The diagnostic accuracy of 3T MRI is comparable to that of MDCT for the preoperative TNM staging of gastric cancer, and for assessing LN metastasis, the addition of DWI to conventional MRI may increase the sensitivity.

MRI at 7 Tesla and above: demonstrated and potential capabilities

With more than 40 installed MR systems worldwide operating at 7 Tesla or higher, ultra-high-field (UHF) imaging has been established as a platform for clinically oriented research in recent years. Along with technical developments that, in part, have also been successfully transferred to lower field strengths, MR imaging and spectroscopy at UHF have demonstrated capabilities and potentials for clinical diagnostics in a variety of studies. In terms of applications, this overview article focuses on already achieved advantages for in vivo imaging, i.e., in imaging the brain and joints of the musculoskeletal system, but also considers developments in body imaging, which is particularly challenging. Furthermore, new applications for clinical diagnostics such as X-nuclei imaging and spectroscopy, which only really become feasible at ultra-high magnetic fields, will be presented.

The regional myocardial microvascular dysfunction differences in hypertrophic cardiomyopathy patients with or without left ventricular outflow tract obstruction: assessment with first-pass perfusion imaging using 3.0-T cardiac magnetic resonance

PURPOSE

To assess regional myocardial microvascular dysfunction differences in hypertrophic cardiomyopathy (HCM) patients with or without left ventricular outflow tract obstruction using 3.0-T cardiac magnetic resonance (CMR) first-pass perfusion imaging.

MATERIALS AND METHODS

Forty-two HCM patients, including 25 HCM patients with left ventricular outflow tract obstruction (HOCM), 17 HCM patients without left ventricular outflow tract obstruction (NOHCM), and 14 healthy subjects underwent CMR. The left ventricular (LV) function, left ventricular end-diastolic wall thickness (EDTH), and diameter of left ventricular outflow tract (LVOT) were measured and calculated. Based on the signal-time curve of the first-pass myocardium perfusion imaging, perfusion parameters including upslope, time to peak, and peak intensity, were assessed and compared by using one-way analysis of variance and independent t tests.

RESULTS

On the first-pass perfusion imaging, lower upslope and peak intensity and longer time to peak were found in HCM patients compared with normal subjects (all p<0.05). In contrast to the NOHCM group, the average time to peak of the HOCM group was increased (13.30 ± 4.82 s vs 16.28 ± 4.90 s, p<0.05), but first-pass perfusion upslope was reduced (4.96 ± 2.55 vs 2.58 ± 0.77, p<0.05). According to the bull's-eye model, the HOCM group's average thickness of basal segments was thicker than the NOHCM group, especially the anteroseptal, inferolateral, and anterior wall values, with a corresponding lower first-pass perfusion upslope than the NOHCM group (all p<0.05). A significant correlation was observed between first-pass perfusion upslope and LV EDTH (r=-0.551, p<0.001) and LVOT diameter (r=0.472, p<0.001).

CONCLUSIONS

The regional myocardial microvascular dysfunction differences in hypertrophic cardiomyopathy (HCM) patients with or without left ventricular outflow tract obstruction can be detected with first-pass perfusion CMR imaging.

Four-channel surface coil array for sequential CW-EPR image acquisition

This article describes a four-channel surface coil array to increase the area of visualization for continuous-wave electron paramagnetic resonance (CW-EPR) imaging. A 776-MHz surface coil array was constructed with four independent surface coil resonators and three kinds of switches. Control circuits for switching the resonators were also built to sequentially perform EPR image acquisition for each resonator. The resonance frequencies of the resonators were shifted using PIN diode switches to decouple the inductively coupled coils. To investigate the area of visualization with the surface coil array, three-dimensional EPR imaging was performed using a glass cell phantom filled with a solution of nitroxyl radicals. The area of visualization obtained with the surface coil array was increased approximately 3.5-fold in comparison to that with a single surface coil resonator. Furthermore, to demonstrate the applicability of this surface coil array to animal imaging, three-dimensional EPR imaging was performed in a living mouse with an exogenously injected nitroxyl radical imaging agent.

Impact of 3.0 T Cardiac MR Imaging Using Dual-Source Parallel Radiofrequency Transmission with Patient-Adaptive B1 Shimming

Objectives

To prospectively evaluate the impact of 3.0 T Cardiac MR imaging using dual-source parallel radiofrequency (RF) transmission with patient-adaptive B1 shimming compared with single-source RF transmission in the RF homogeneity, image contrast and image quality.

Methods

The study was approved by the local institutional review board, and all subjects provided written informed consent. Fourteen healthy volunteers were examined at 3.0 T MR, with both the conventional single-source and the new dual-source RF transmission. B1 calibrations (RF shimming) of the heart region were performed to acquire a percent of the prescribed flip angle (FA) of B1 maps, which were used for quantitative assessment of RF homogeneity. Contrast ratios (CRs) between ventricular blood pool and septum were calculated on balanced-turbo field echo (B-TFE) cine images. The off-resonance artifacts of cine images were blindly assessed by two radiologists according to a 4-point grading-scale.

Results

A significantly lower mean coefficients of variance of the achieved FA with dual-source revealed better RF homogeneity compared to single-source (P = 0.0094). Dual-source RF shimming significantly increased the CRs (P<0.05) and reduced the off-resonance artifacts of B-TFE cine images (P<0.05). Inter-observer agreement for the off-resonance artifacts of B-TFE cine images was good to excellent (k >0.65).

Conclusions

Dual-source parallel RF transmission significantly improves the RF homogeneity, increases image contrast and reduces image artifacts of cardiac B-TFE images compared to single-source mode. This may be of value in reducing the observer-dependence of cardiac MR images and enhancing diagnostic confidence for clinical practice using CMR at 3.0 T.

Breast MR imaging at 3 T with dual-source radiofrequency transmission offers superior B1 homogeneity: an intraindividual comparison with breast MR imaging at 1.5 T

PURPOSE

To evaluate and compare B1 homogeneity for breast magnetic resonance (MR) imaging performed at 3 T with dual-source radiofrequency (RF) transmission to 1.5-T MR imaging and 3-T MR imaging with quadrature transmission.

MATERIALS AND METHODS

This prospective study received institutional review board approval and patients provided informed consent. Women (n = 25; mean age, 53 years; range, 30-68 years) suspected of having breast lesions underwent breast MR imaging examinations on comparable 1.5-T and 3-T clinical systems between February and May 2012. B1 maps were obtained at 1.5 T and at 3 T with quadrature and dual-source RF transmission. Intrabreast differences and differences in mean B1 values between right and left breasts were investigated by using two-sided multivariate analysis of variance with interaction; t tests were used to compare the differences between measured whole-breast mean B1 values and requested B1 values.

RESULTS

With quadrature transmission at 1.5 T and 3 T, the mean B1 values showed a statistically significant difference: left-breast measured B1 was -8.9% of requested B1 value at 1.5 T and -13.7% at 3 T (P < .001), whereas right-breast measured B1 was +5.4% of requested B1 value at 1.5 T (P < .001) and +2.7% at 3 T (P = .01). With dual-source RF transmission at 3 T, mean B1 values across the breasts were not statistically different, nor were the measured B1 values compared with requested B1 values (left breast, -0.6%; right breast, -0.7%). At 3 T with dual-source transmission, slight intrabreast local variations in B1 were recorded.

CONCLUSION

MR imaging at 3 T with dual-source RF transmission offered an overall B1 homogeneity for breast imaging that was better than that obtained at 1.5 T and with quadrature transmission.

Multidisciplinary management of hepatocellular carcinoma

Treatment of HCC is complicated by its highly variable biologic behavior and the frequent coexistence of chronic liver disease and cirrhosis in affected patients. While surgery remains the most frequently employed treatment modality, curative resection is only possible for a minority of patients. More often, treatment goals are palliative and draw on the expertise of a range of medical specialists. This chapter aims to place current treatment strategies within the framework of a multidisciplinary approach with special emphasis on pretreatment evaluation, staging, and the selection of an appropriate treatment strategy.

Assessment of perfusion in normal carpal bones with dynamic gadolinium-enhanced MRI at 3 Tesla

PURPOSE

To investigate the normal enhancement patterns of the scaphoid, lunate, and capitate bones with dynamic contrast-enhanced magnetic resonance imaging (MRI).

MATERIALS AND METHODS

The study was approved by the hospital's Ethics Committee. Nineteen volunteers (13 female, 6 male; mean age 38 years) were examined and all gave written consent. Perfusion was assessed at 3 Tesla using dynamic contrast-enhanced MRI. After two-dimensional (2D) motion correction of the data set, regions of interest were placed in the capitate, lunate, and distal and proximal pole of scaphoid bone and from the mean signal intensities (SI), the enhancement was computed. The four locations were compared for time to peak, delay time, maximum enhancement, and maximum slope using Friedman's two-way analysis of variance.

RESULTS

Typical SI versus time curves revealed two components: a faster component with strong contrast enhancement and a slow component with prolonged enhancement. The mean value (standard deviation, SD) for maximum enhancement was 51 (33)% in the capitate, 54 (25)% in the lunate, 51 (34)% in the proximal pole and 51 (28)% in the distal pole of the scaphoid. The result of the Friedman test showed no significant difference (P < 0.05) in the perfusion variables between the capitate, lunate, and distal and proximal scaphoid bones.

CONCLUSION

Assessment of perfusion in normal carpal bone using contrast-enhanced MRI is possible. Optimization of the method and understanding of the normal perfusion may allow evaluation of pathological conditions such as osteonecrosis.

Ocular volumetry using fast high-resolution MRI during visual fixation

BACKGROUND AND PURPOSE

Volumetry may be useful for evaluating treatment response and prognosis of intraocular lesions. Phantom, volunteer, and patient studies were performed to determine whether ocular MR volumetry is reproducible.

MATERIALS AND METHODS

Half-Fourier single-shot RARE and FSPGR sequences at 1.5T with a 76-mm-diameter surface coil were optimized to obtain still ocular images. Volumetry accuracies of each sequence were compared with simulated subretinal phantom volumes. Ocular volumetry was performed in 15 volunteers twice in 1 week by using contiguous axial images of the globes while the subjects stared at a target, and images were acquired in 2 seconds before the subjects were instructed to blink, with this process repeated as necessary. Imaging, intraobserver, and interobserver reproducibility for volumes of the whole eyeball and anterior chamber were assessed. Ocular volumetry was also performed in 6 patients with intraocular tumors before and after treatment.

RESULTS

The phantom study demonstrated that measurement error rates with RARE were significantly lower than with FSPGR (P<.01). The volunteer study demonstrated excellent imaging and intraobserver reproducibility of RARE volumetry for whole eyeballs and anterior chambers (P<.01). Although no interobserver differences were observed in anterior chamber volume measurement (P=.33), there was a significant difference between the 2 observers in eyeball volume measurement (P<.01). Follow-up volumetric data were useful for treatment decisions in all patients.

CONCLUSIONS

Ocular volumetry from contiguous ultrafast RARE images obtained during visual fixation is feasible in volunteer and patient studies and is superior to FSPGR images.

Rectal imaging: part 2, Perianal fistula evaluation on pelvic MRI--what the radiologist needs to know

OBJECTIVE

The purpose of this article is to provide an overview of pelvic MRI for the evaluation of perianal fistulas, with a description of the technique, illustration of relevant normal anatomy, and examples of various fistula types.

CONCLUSION

MRI evaluation of perianal fistulas can be challenging, and knowledge of relevant pelvic anatomy and fistula classification remains crucial in the diagnosis. MRI is highly accurate for fistula depiction and, by providing an accurate assessment of disease status and extension, can help surgical planning to minimize recurrence and detect clinically unapparent disease.

Free-breathing inner-volume black-blood imaging of the human heart using two-dimensionally selective local excitation at 3 T

Black-blood fast spin-echo imaging is a powerful technique for the evaluation of cardiac anatomy. To avoid fold-over artifacts, using a sufficiently large field of view in phase-encoding direction is mandatory. The related oversampling affects scanning time and respiratory chest motion artifacts are commonly observed. The excitation of a volume that exclusively includes the heart without its surrounding structures may help to improve scan efficiency and minimize motion artifacts. Therefore, and by building on previously reported inner-volume approach, the combination of a black-blood fast spin-echo sequence with a two-dimensionally selective radiofrequency pulse is proposed for selective "local excitation" small field of view imaging of the heart. This local excitation technique has been developed, implemented, and tested in phantoms and in vivo. With this method, small field of view imaging of a user-specified region in the human thorax is feasible, scanning becomes more time efficient, motion artifacts can be minimized, and additional flexibility in the choice of imaging parameters can be exploited.

MR imaging techniques for pancreas

Pancreatic magnetic resonance (MR) imaging has become a useful tool in evaluating pancreatic disorders. Technical innovations in MR imaging have evolved over the last decade, with most sequences being performed in one or a few breath-holds. Three-dimensional sequences with thin, contiguous slices allow for improved spatial resolution on the postgadolinium images and MR cholangiopancreatography (MRCP). The diagnostic potential of MRCP is equivalent to endoscopic retrograde pancreatography, particularly when intravenous secretin is used to enhance the pancreatic duct assessment. This article highlights the advantages and disadvantages of state-of-the-art and emerging pulse sequences and their application to imaging pancreatic diseases.

Gadoxetate disodium-enhanced magnetic resonance imaging versus contrast-enhanced 18F-fluorodeoxyglucose positron emission tomography/computed tomography for the detection of colorectal liver metastases

PURPOSE

: To compare the diagnostic accuracy of gadoxetate disodium-enhanced magnetic resonance imaging (EOB-MRI) on a 3-T system and integrated contrast-enhanced F-fluorodeoxyglucose positron emission tomography/computed tomography (CE-PET/CT) for the detection of hepatic metastases from colorectal cancers.

MATERIALS AND METHODS

: The approval from the institutional review board was obtained, and the requirement for informed consent was waived. We retrospectively evaluated 135 metastases in 68 patients (37 men, 31 women; mean age: 68 years; age range: 37-82 years) who underwent both EOB-MRI and CE-PET/CT. A total of 103 metastases were confirmed during surgery and 32 were confirmed by imaging findings during follow-up. The images were independently reviewed by 2 observers. The diagnostic accuracies of EOB-MRI and CE-PET/CT were determined by calculating the areas under each reader-specific receiver operating characteristic curve (Az). Patient-based lesion sensitivity and specificity were compared using the McNemar test.

RESULTS

: The mean area under the Az on EOB-MRI versus CE-PET/CT was 0.94 versus 0.81 for all lesions (P < 0.001), 0.92 versus 0.60 for lesions ≤1 cm in size (P < 0.001), and 0.88 versus 0.96 for lesions >1 cm (P = 0.098), respectively. The sensitivity, specificity, positive predictive values, and negative predictive value on a patient basis were 100%, 71%, 97%, and 100% for EOB-MRI and 93%, 71%, 97%, and 57% for CE-PET/CT, respectively.

CONCLUSIONS

: EOB-MRI using a 3-T system is more accurate than CE-PET/CT, especially for the detection of small (≤1.0 cm) lesions. Patient-based analysis revealed that EOB-MRI has a higher sensitivity and negative predictive value than CE-PET/CT.

Focal liver lesions at 3.0 T: lesion detectability and image quality with T2-weighted imaging by using conventional and dual-source parallel radiofrequency transmission

PURPOSE

To prospectively compare T2-weighted single-shot turbo spin-echo (TSE) sequences performed with parallel and conventional radiofrequency (RF) transmission at 3.0 T for liver lesion detection, image quality, lesion conspicuity, and lesion contrast.

MATERIALS AND METHODS

After written informed consent and institutional review board approval, 52 consecutive patients (32 men, 20 women; mean age, 56.6 years ± 13.7 [standard deviation]) underwent routine magnetic resonance (MR) imaging with a clinical 3.0-T unit. Two independent readers reviewed images acquired with conventional and dual-source parallel RF transmission for detection of focal liver lesions, with separate reading of a third radiologist, including all available imaging findings, clinical history, and histopathologic findings, as reference. Image quality and lesion conspicuity were rated on five- and three-point evaluation scales, respectively. Contrast ratios between focal liver lesions and adjacent liver parenchyma were calculated. Significance was determined by using nonparametric Wilcoxon signed-rank and marginal homogeneity tests.

RESULTS

With the reference standard, 106 index lesions were identified in 22 patients. Detection rate significantly improved from 87% (92 of 106) to 97% (103 of 106) (reader 1) and from 85% (90 of 106) to 96% (102 of 106) (reader 2) with parallel RF transmission (reader 1, P = .0078; reader 2, P = .002). Quality of parallel RF transmission images was assigned scores significantly higher, compared with quality of conventional RF transmission images (mean for reader 1, 2.88 ± 0.73 vs 4.04 ± 0.44; mean for reader 2, 2.81 ± 0.72 vs 4.04 ± 0.39; P < .0001 for both). Lesion conspicuity scores were significantly higher on parallel RF transmission images, compared with conventional RF transmission images (mean for reader 1, 2.02 ± 0.64 vs 2.92 ± 0.27; mean for reader 2, 2.06 ± 0.67 vs 2.90 ± 0.30; P < .0001 for both). Contrast ratios were significantly higher with parallel RF transmission (P < .05).

CONCLUSION

Compared with conventional RF transmission, parallel RF transmission significantly improved liver lesion detection rate, image quality, lesion conspicuity, and lesion contrast.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.11101429/-/DC1.

Cardiovascular magnetic resonance physics for clinicians: part I

There are many excellent specialised texts and articles that describe the physical principles of cardiovascular magnetic resonance (CMR) techniques. There are also many texts written with the clinician in mind that provide an understandable, more general introduction to the basic physical principles of magnetic resonance (MR) techniques and applications. There are however very few texts or articles that attempt to provide a basic MR physics introduction that is tailored for clinicians using CMR in their daily practice. This is the first of two reviews that are intended to cover the essential aspects of CMR physics in a way that is understandable and relevant to this group. It begins by explaining the basic physical principles of MR, including a description of the main components of an MR imaging system and the three types of magnetic field that they generate. The origin and method of production of the MR signal in biological systems are explained, focusing in particular on the two tissue magnetisation relaxation properties (T1 and T2) that give rise to signal differences from tissues, showing how they can be exploited to generate image contrast for tissue characterisation. The method most commonly used to localise and encode MR signal echoes to form a cross sectional image is described, introducing the concept of k-space and showing how the MR signal data stored within it relates to properties within the reconstructed image. Before describing the CMR acquisition methods in detail, the basic spin echo and gradient pulse sequences are introduced, identifying the key parameters that influence image contrast, including appearances in the presence of flowing blood, resolution and image acquisition time. The main derivatives of these two pulse sequences used for cardiac imaging are then described in more detail. Two of the key requirements for CMR are the need for data acquisition first to be to be synchronised with the subject's ECG and to be fast enough for the subject to be able to hold their breath. Methods of ECG synchronisation using both triggering and retrospective gating approaches, and accelerated data acquisition using turbo or fast spin echo and gradient echo pulse sequences are therefore outlined in some detail. It is shown how double inversion black blood preparation combined with turbo or fast spin echo pulse sequences acquisition is used to achieve high quality anatomical imaging. For functional cardiac imaging using cine gradient echo pulse sequences two derivatives of the gradient echo pulse sequence; spoiled gradient echo and balanced steady state free precession (bSSFP) are compared. In each case key relevant imaging parameters and vendor-specific terms are defined and explained.

Cardiovascular magnetic resonance at 3.0 T: current state of the art

There are advantages to conducting cardiovascular magnetic resonance (CMR) studies at a field strength of 3.0 Telsa, including the increase in bulk magnetization, the increase in frequency separation of off-resonance spins, and the increase in T1 of many tissues. However, there are significant challenges to routinely performing CMR at 3.0 T, including the reduction in main magnetic field homogeneity, the increase in RF power deposition, and the increase in susceptibility-based artifacts.In this review, we outline the underlying physical effects that occur when imaging at higher fields, examine the practical results these effects have on the CMR applications, and examine methods used to compensate for these effects. Specifically, we will review cine imaging, MR coronary angiography, myocardial perfusion imaging, late gadolinium enhancement, and vascular wall imaging.

[A fundamental study of non-contrast enhanced MR angiography using ECG gated-3D fast spin echo at 3.0 T]

Contrast-enhanced magnetic resonance angiography (CE-MRA) is frequently performed in body and extremity studies because of its superior ability to detect the vascular stenosis. However, nephrotoxicity of the contrast medium has been emphasized in recent years. Non-contrast MRA using the three-dimensional electrocardiogram-synchronized fast spin echo method (FBI, NATIVE and TRANCE) is recommended as a substitute for CE-MRA. There are a few reports in the literature that evaluate the detectability of vascular stenosis using non-contrast MRA on 3.0 T MRI. The purpose of this study was to evaluate the detectability of vascular stenosis using non-contrast MRA at 3.0 T with an original vascular phantom. The vascular phantom consisted of silicon tubes. 30% and 70% stenosis of luminal diameter were made. Each silicon tube connected a pump producing a pulsatile flow. A flowing material to was used in this study to show the similarity of the intensity to blood on MRI. MRA without a contrast medium (NATIVE sequence) were performed in the vascular phantom by changing the image matrix, static magnetic field strength and flow velocity. In addition, the NATIVE sequence was used with or without flow compensation. Vascular stenosis was quantitatively estimated by measurement of the signal intensities in non-contrast MRA images. MRA with NATIVE sequence demonstrated an accurate estimation of 30% vascular stenosis at slow flow velocity. However, 30% stenosis was overestimated in cases of high flow velocity. Estimation was improved by using a flow compensation sequence. 70% stenosis was overestimated on MRA with NATIVE sequence. Estimation of 70% stenosis was improved by using a flow compensation sequence. Accurate estimation of vascular stenosis in MRA with a NATIVE sequence is improved by using the flow compensation technique. MRA with NATIVE sequence is considered to be a promising method for the evaluation of patients with severe renal dysfunction as a substitute for CT angiography or CE-MRA.

State-of-the-art pancreatic MRI

OBJECTIVE

The purpose of this article is to discuss the most current techniques used for pancreatic imaging, highlighting the advantages and disadvantages of state-of-the-art and emerging pulse sequences and their application to pancreatic disease.

CONCLUSION

Given the technologic advances of the past decade, pancreatic MRI protocols have evolved. Most sequences can now be performed in one or a few breath-holds; 3D sequences with thin, contiguous slices offer improved spatial resolution; and better fat and motion suppression allow improved contrast resolution and image quality. The diagnostic potential of MRCP is now almost as good as ERCP, with pancreatic MRI as the main imaging technique to investigate biliopancreatic pain, chronic pancreatitis, and cystic pancreatic tumors at many institutions. In addition, functional information is provided with secretin-enhanced MRCP.