Abdominal MR imaging with a volumetric interpolated breath-hold examination

Clinical, ethical and financial implications of incidental imaging findings: experience from a phase I trial in healthy elderly volunteers

Background

The detection of incidental findings (IF) in magnetic resonance imaging (MRI) studies is common and increases as a function of age. Responsible handling of IF is required, with implications for the conduct of research and the provision of good clinical care.

Aim

To investigate the prevalence and clinical significance of IF in a prospective cohort of healthy elderly volunteers who underwent MRI of the torso as a baseline investigation for a phase I trial. We assessed the follow-up pathway with consequent cost implications and impact on trial outcomes.

Methods

A total of 29 elderly healthy volunteers (mean age 67, range 61–77, 59% female) were eligible at screening and underwent MRI for assessment of visceral and subcutaneous fat.

Results

IF were detected in 19 subjects (66%). Suspected IF of high and low clinical significance were found in 14% and 52% of participants, respectively. Follow up of IF was conducted in 18 individuals, confirming abnormalities in 13 subjects, 3 of whom were recommended for deferred clinical re-evaluation. The remaining 5 subjects had false positive IF based on second line imaging tests. Costs of follow-up medical care were considerable.

Conclusion

MRI abnormalities are common in elderly individuals, as a result of age and non-diagnostic quality of research scans. In the presence of IF in the context of clinical trials, immediate referrals and follow up assessments may be required to rule out suspected pathology prior to exposing trial participants to investigational medicine products (IMP). Unanticipated costs, ethical implication and the possible impact of IF on trial outcomes need to be taken into account when designing and conducting trials with an IMP.

Optimization of the dynamic, Gd-EOB-DTPA-enhanced MRI of the liver: the effect of the injection rate

BACKGROUND

Tissue-specific gadolinium-based contrast agents such as Gd-BOPTA, Gd-EOB-DTPA are increasingly used for liver imaging. Despite the added value of the hepatobiliary phase a proper arterial phase is still critical, especially in patients with chronic liver diseases. So far, there are limited data in the literature about the effect of the injection speed of Gd-EOB-DTPA in liver and vessel enhancement.

PURPOSE

To evaluate the effect of injection rate on the enhancement of liver parenchyma and vasculature in Gd-EOB-DTPA-enhanced liver MRI.

MATERIAL AND METHODS

Eighty patients who underwent Gd-EOB-DTPA-enhanced liver MRI (1.5T multi-channel MR-system) were retrospectively evaluated. We used a Care Bolus technique with an injection rate of 2 mL/s in group 1 (n = 40) and a Care Bolus technique with an injection rate of 1 mL/s in group 2 (n = 40) to determine the start of the arterial-dominant phase. Signal intensities were measured in vascular structures and liver parenchyma. Signal-to-noise-ratio (SNR), SNR increase (SNRi), and percentage enhancement (PE) were calculated and compared by a students t-test.

RESULTS

The SNR, SNRi, and PE of the aorta in the arterial phase were significantly higher in group 2 in comparison to group 1 (P = 0.007, P = 0.0043, and P < 0.001, respectively). There were no significant differences concerning the SNR, SNRi, or PE of the portal vein and the normal liver parenchyma between both groups at all time points.

CONCLUSION

The study shows that a lower injection rate of 1 mL/s enables a higher enhancement in the aorta in the arterial phase compared with Gd-EOB-DTPA-enhanced MRI with the more commonly used injection rate of 2 mL/s.

Differentiation of malignant and benign breast lesions using magnetization transfer imaging and dynamic contrast-enhanced MRI

PURPOSE

To evaluate feasibility of using magnetization transfer ratio (MTR) in conjunction with dynamic contrast-enhanced MRI (DCE-MRI) for differentiation of benign and malignant breast lesions at 3 Tesla.

MATERIALS AND METHODS

This prospective study was IRB and HIPAA compliant. DCE-MRI scans followed by MT imaging were performed on 41 patients. Regions of interest (ROIs) were drawn on co-registered MTR and DCE postcontrast images for breast structures, including benign lesions (BL) and malignant lesions (ML). Initial enhancement ratio (IER) and delayed enhancement ratio (DER) were calculated, as were normalized MTR, DER, and IER (NMTR, NDER, NIER) values. Diagnostic accuracy analysis was performed.

RESULTS

Mean MTR in ML was lower than in BL (P < 0.05); mean DER and mean IER in ML were significantly higher than in BL (P < 0.01, P < 0.001). NMTR, NDER, and NIER were significantly lower in ML versus BL (P < 0.007, P < 0.001, P < 0.001). IER had highest diagnostic accuracy (77.6%), sensitivity (86.2%), and area under the ROC curve (.879). MTR specificity was 100%. Logistic regression modeling with NMTR and NIER yielded best results for BL versus ML (sensitivity 93.1%, specificity 80%, AUC 0.884, accuracy 83.7%).

CONCLUSION

Isolated quantitative DCE analysis may increase specificity of breast MR for differentiating BL and ML. DCE-MRI with NMTR may produce a robust means of evaluating breast lesions.

Angiomyolipoma with minimal fat: can it be differentiated from clear cell renal cell carcinoma by using standard MR techniques?

PURPOSE

To retrospectively assess whether magnetic resonance (MR) imaging with opposed-phase and in-phase gradient-echo (GRE) sequences and MR feature analysis can differentiate angiomyolipomas (AMLs) that contain minimal fat from clear cell renal cell carcinomas (RCCs), with particular emphasis on small (<3-cm) masses.

MATERIALS AND METHODS

Institutional review board approval and a waiver of informed consent were obtained for this HIPAA-compliant study. MR images from 108 pathologically proved renal masses (88 clear cell RCCs and 20 minimal fat AMLs from 64 men and 44 women) at two academic institutions were evaluated. The signal intensity (SI) of each renal mass and spleen on opposed-phase and in-phase GRE images was used to calculate an SI index and tumor-to-spleen SI ratio. Two radiologists who were blinded to the pathologic results independently assessed the subjective presence of intravoxel fat (ie, decreased SI on opposed-phase images compared with that on in-phase images), SI on T1-weighted and T2-weighted images, cystic degeneration, necrosis, hemorrhage, retroperitoneal collaterals, and renal vein thrombosis. Results were analyzed by using the Wilcoxon rank sum test, two-tailed Fisher exact test, and multivariate logistic regression analysis for all renal masses and for small masses. A P value of less than .05 was considered to indicate a statistically significant difference.

RESULTS

There were no differences between minimal fat AMLs and clear cell RCCs for the SI index (8.05%±14.46 vs 14.99%±19.9; P=.146) or tumor-to-spleen ratio (-8.96%±16.6 and -15.8%±22.4; P=.227) when all masses or small masses were analyzed. Diagnostic accuracy (area under receiver operating characteristic curve) for the SI index and tumor-to-spleen ratio was 0.59. Intratumoral necrosis and larger size were predictive of clear cell RCC (P<.001) for all lesions, whereas low SI (relative to renal parenchyma SI) on T2-weighted images, smaller size, and female sex correlated with minimal fat AML (P<.001) for all lesions.

CONCLUSION

The diagnostic accuracy of opposed-phase and in-phase GRE MR imaging for the differentiation of minimal fat AML and clear cell RCC is poor. In this cohort, low SI on T2-weighted images relative to renal parenchyma and small size suggested minimal fat AML, whereas intratumoral necrosis and large size argued against this diagnosis.

Can diffusion-weighted magnetic resonance imaging (DW-MRI) alone be used as a reliable sequence for the preoperative detection and characterisation of hepatic metastases? A meta-analysis

PURPOSE

To perform a meta-analysis of all available studies of the diagnostic performance of diffusion-weighted magnetic resonance imaging (DW-MRI) in patients with hepatic metastases.

METHODS

Databases including MEDLINE and EMBASE were searched for relevant original articles published from January 2000 to February 2012. We determined sensitivities and specificities across studies, calculated positive and negative likelihood ratios (LR+ and LR-), diagnostic odds ratio (DOR) and constructed summary receiver operating characteristic curves using hierarchical regression models.

RESULTS

Across 11 studies (537 patients), DW-MRI sensitivity was 0.87 (95%confidence interval (CI), 0.80, 0.91) and specificity was 0.90 (95%CI, 0.86, 0.93). Overall, LR+ was 8.52 (95%CI, 6.17, 11.77), LR- was 0.15 (95%CI, 0.10, 0.22) and DOR was 57.36 (95%CI, 38.29, 85.93). In studies in which both DW-MRI and contrast-enhanced magnetic resonance imaging (CE-MRI) were performed, the comparison of DW-MRI performance with that of CE-MRI suggested no major differences against these two methods (p>0.05). DW-MRI combined CE-MRI had higher sensitivity and specificity than DW-MRI alone (97% versus 86% and 91% versus 90%, respectively) (p<0.05). The subgroup in which DW-MRI examinations were performed with a 3.0 Tesla (T) device had higher pooled specificity (0.91, 95%CI, 0.88-0.95) than the subgroup of DW-MRI with 1.5 T device (0.81, 95%CI, 0.67, 0.94) (p<0.05). Average lesion size (≤ 1.5 cm versus >1.5cm) did not influence the diagnostic accuracy of the test (p>0.05).

CONCLUSION

Our results demonstrate DW-MRI has good diagnostic performance in the overall evaluation of hepatic metastases and equivalent to CE-MRI. Combination of CE-MRI and DW-MRI can improve the diagnostic accuracy of magnetic resonance (MR) imaging. Our study further confirms that DW-MRI can accurately detect hepatic metastases regardless of the lesion size. It is suggested to perform DW-MRI by 3.0 T devices, which might have high specificity to identify liver metastases.

Two- versus three-dimensional dual gradient-echo MRI of the liver: a technical comparison

OBJECTIVE

To compare 2D spoiled dual gradient-echo (SPGR-DE) and 3D SPGR-DE with fat and water separation for the assessment of focal and diffuse fatty infiltration of the liver.

METHODS

A total of 227 consecutive patients (141 men; 56 ± 14 years) underwent clinically indicated liver MRI at 1.5 T including multiple-breath-hold 2D SPGR-DE and single-breath-hold 3D SPGR-DE with automatic reconstruction of fat-only images. Two readers assessed the image quality and number of fat-containing liver lesions on 2D and 3D in- and opposed-phase (IP/OP) images. Liver fat content (LFC) was quantified in 138 patients without chronic liver disease from 2D, 3D IP/OP, and 3D fat-only images.

RESULTS

Mean durations of 3D and 2D SPGR-DE acquisitions were 23.7 ± 2.9 and 97.2 ± 9.1 s respectively. The quality of all 2D and 3D images was rated diagnostically. Three-dimensional SPGR-DE revealed significantly more breathing artefacts resulting in lower image quality (P < 0.001); 2D and 3D IP/OP showed a similar detection rate of fat-containing lesions (P = 0.334) and similar LFC estimations (mean: +0.4 %; P = 0.048). LFC estimations based on 3D fat-only images showed significantly higher values (mean: 2.7 % + 3.5 %) than those from 2D and 3D IP/OP images (P < 0.001).

CONCLUSION

Three dimensional SPGR-DE performs as well as 2D SPGR-DE for the assessment of focal and diffuse fatty infiltration of liver parenchyma. The 3D SPGR-DE sequence used was quicker but more susceptible to breathing artefacts. Significantly higher LFC values are derived from 3D fat-only images than from 2D or 3D IP/OP images.

Thoracic and abdominal aortic diameter measurement by MRI using plain axial volumetric interpolated breath-hold examination in epidemiologic research: a validation study

RATIONALE AND OBJECTIVES

This study evaluates the validity and reliability of measuring the diameters of the thoracic and abdominal aorta from plain volumetric interpolated breath-hold examination (VIBE) images.

MATERIALS AND METHODS

The study included 50 male subjects from the population-based Study of Health in Pomerania. They underwent imaging of the thoracic and abdominal aorta at 1.5 Tesla using a contrast-enhanced magnetic resonance angiography (CE-MRA) and plain VIBE sequence. Diameters were measured at five predefined anatomic sites from reformatted orthogonal CE-MRA images and axial plain VIBE images. The measurements were validated using Pearson correlation and Bland-Altman analysis. The Bland-Altman method was also used to assess reliability.

RESULTS

Comparison of the diameters measured from CE-MRA and VIBE images revealed strong correlation for the ascending, descending, suprarenal, and infrarenal aorta with r = 0.95 (P < .0001), r = 0.88 (P < .0001), 0.92 (P < .0001), and 0.87 (P < .0001), respectively. Measurement for the aortic arch was moderately correlated with r = 0.78 (P < .0001). Mean bias did not exceed 0.1 cm (6%). The 95% limits of agreement (LOA) were less than 0.5 cm (15%). Intra- and interobserver agreement showed a mean bias of less than 2%; the 95% LOA were less than 11%.

CONCLUSIONS

Axial measurement of the diameters of the thoracic and abdominal aorta using a plain axial VIBE sequence is highly valid and reliable, making it suitable for use in epidemiologic research.

Characterization of hepatic adenoma and focal nodular hyperplasia with gadoxetic acid

PURPOSE

To characterize imaging features of histologically proven hepatic adenoma (HA) as well as histologically and/or radiologically proven focal nodular hyperplasia (FNH) using delayed hepatobiliary MR imaging with 0.05 mmol/kg gadoxetic acid.

MATERIALS AND METHODS

Five patients with six HAs with histological correlation were retrospectively identified on liver MRI studies performed with gadoxetic acid, and T1-weighted imaging acquired during the delayed hepatobiliary phase. Additionally, 23 patients with 34 radiologically diagnosed FNH lesions (interpreted without consideration of delayed imaging) were identified, two of which also had histological confirmation. Signal intensity ratios relative to adjacent liver were measured on selected imaging sequences.

RESULTS

All six hepatic adenomas (100%), which had histological confirmation, demonstrated hypointensity relative to adjacent liver on delayed imaging. Furthermore, all of the FNH (including 34 radiologically proven, 2 of which were also histologically proven) were either hyperintense (23/34, 68%) or isointense (11/34, 32%) relative to the adjacent liver on delayed imaging. None of the FNHs were hypointense relative to liver.

CONCLUSION

Distinct imaging characteristics of HA versus FNH on delayed gadoxetic acid-enhanced MRI, with adenomas being hypointense and FNH being iso- or hyperintense on delayed imaging may improve specificity for characterization, and aid in the differentiation of these two lesions.

Increased pancreatic fat fraction is present in obese adolescents with metabolic syndrome

OBJECTIVES

Little is known about pancreatic fat accumulation and its possible associations with metabolic syndrome (MetS) and glucose metabolism. The aim of the present study was to quantify pancreatic fat fraction (PFF) in lean and obese adolescents and explore its relation to metabolic parameters.

METHODS

We recruited 25 lean and 24 obese adolescents. PFF and visceral adipose tissue (VAT) were determined using magnetic resonance imaging. We measured blood pressure, fasting glucose, insulin, liver enzymes, leptin, and lipid levels. Obese subjects underwent an oral glucose tolerance test.

RESULTS

PFF was significantly higher in obese than in lean subjects (4.8±1.2 vs 3.6±0.9; P<0.001) and was associated with VAT, γ-glutamyltransferase, triglycerides, high-density lipoprotein cholesterol, leptin concentrations, and MetS (P<0.05 for all). None of the obese subjects had glucose intolerance, but when adjusted for VAT, the following 3 parameters correlated negatively with PFF: fasting and 30- minute and 120-minute insulin levels. We divided subjects into 3 groups: group I, lean without MetS; group II, obese without MetS; and group III, obese with MetS, and observed that PFF increased gradually among groups (I: 3.56%±0.88%; II: 4.70%±1.06%; III: 5.34%±1.49%; P<0.001).

CONCLUSIONS

Obese adolescents accumulate fat in the pancreas. PFF correlates with the presence of MetS. Even in the absence of glucose intolerance, pancreatic fat deposition is associated with impaired insulin response to glucose overload. This suggests that β-cell dysfunction may already be present in nondiabetic obese adolescents, mirroring what has been shown in adults, and that pancreatic fat accumulation may participate in obesity-associated pancreatic endocrine dysfunction.

High resolution navigated three-dimensional T₁-weighted hepatobiliary MRI using gadoxetic acid optimized for 1.5 Tesla

PURPOSE

To determine optimal delay times and flip angles for T1-weighted hepatobiliary imaging at 1.5 Tesla (T) with gadoxetic acid and to demonstrate the feasibility of using a high-resolution navigated optimized T1-weighted pulse sequence to evaluate biliary disease.

MATERIALS AND METHODS

Eight healthy volunteers were scanned at 1.5T using a T1-weighted three-dimensional (3D)-SPGR pulse sequence following the administration of 0.05 mmol/kg of gadoxetic acid. Navigator-gating enabled acquisition of high spatial resolution (1.2 × 1.4 × 1.8 mm(3) , interpolated to 0.7 × 0.7 × 0.9 mm(3) ) images in approximately 5 min of free-breathing. Multiple breath-held acquisitions were performed at flip angles between 15° and 45° to optimize T1 weighting. To evaluate the performance of this optimized sequence in the setting of biliary disease, the image quality and biliary excretion of 51 consecutive clinical scans performed to assess primary sclerosing cholangitis (PSC) were evaluated.

RESULTS

Optimal hepatobiliary imaging occurs at 15-25 min, using a 40° flip angle. The image quality and visualization of biliary excretion in the PSC scans were excellent, despite the decreased liver function in some patients. Visualization of reduced excretion often provided diagnostic information that was unavailable by conventional magnetic resonance cholangiopancreatography (MRCP).

CONCLUSION

High-resolution navigated 3D-SPGR hepatobiliary imaging using gadoxetic acid and optimized scan parameters is technically feasible and can be clinically useful, even in patients with decreased hepatobiliary function.

MR imaging of pulmonary embolism: diagnostic accuracy of contrast-enhanced 3D MR pulmonary angiography, contrast-enhanced low-flip angle 3D GRE, and nonenhanced free-induction FISP sequences

PURPOSE

To evaluate relative detection of pulmonary embolism (PE) with standard bolus-triggered contrast-enhanced breath-hold magnetic resonance (MR) pulmonary angiography, contrast-enhanced recirculation-phase breath-hold low-flip angle three-dimensional (3D) gradient-echo (GRE), and nonenhanced free-induction cardiac- and respiratory-triggered true fast imaging with steady-state precession (FISP) MR sequences.

MATERIALS AND METHODS

The study was HIPAA compliant and institutional review board approved. Twenty-two patients with a computed tomographic (CT) angiography diagnosis of PE underwent MR imaging within 48 hours of CT. MR included three complementary techniques: MR pulmonary angiography, 3D GRE, and triggered true FISP. Each sequence was analyzed separately by two independent reviewers who recorded presence of emboli in categorized pulmonary artery anatomic territories. CT angiography results were analyzed by a third independent reviewer, who retrospectively recorded presence of emboli using the same format; these results served as the reference standard. Sensitivity, specificity, and positive and negative predictive values for PE detection were calculated for each MR technique on a per-embolus basis, and 95% confidence intervals were calculated according to the efficient-score method. A two-sample t test was used to compare values among MR techniques.

RESULTS

Sensitivities for PE detection were 55% for MR pulmonary angiography, 67% for triggered true FISP, and 73% for 3D GRE MR imaging. Combining all three MR sequences improved overall sensitivity to 84%. Specificity was 100% for all detection methods except for MR pulmonary angiography (one false-positive). Agreement between readers was high (κ = 0.87). Embolus detection rates were lowest in the lingula branch for all MR sequences compared with remainder of the vascular territories (P = .07).

CONCLUSION

There are complementary benefits to combining standard MR pulmonary angiography, 3D GRE, and triggered true FISP MR examinations for evaluation of PE.

Gadoxetic acid-enhanced T1-weighted MR cholangiography in primary sclerosing cholangitis

PURPOSE

To investigate the value of gadoxetic acid-enhanced three-dimensional T1-weighted MR cholangiography (T1w-MRC) in comparison to three-dimensional T2-weighted MR cholangiopancreaticography (T2w-MRCP) in patients with primary sclerosing cholangitis (PSC).

MATERIALS AND METHODS

Thirty-four MR exams in 29 patients (46.0 ± 16.1 years; 19 men, 10 women) scanned within a 14-month period were retrospectively included. Two abdominal radiologists independently evaluated image quality regarding image contrast, image quality degradation due to artifacts, and visualization quality of ducts. The order of biliary tree branches that were visualized and reader preference toward each method were recorded. Helpfulness of T1w-MRC was scored in consensus. Confirmatory endoscopic retrograde cholangiopancreaticography (ERCP) performed within 3 months of the MR examination was available in 8 patients.

RESULTS

Image quality of T1w-MRC and T2w-MRCP was graded good to excellent in all cases. There were advantages for both T1w-MRC (functional information, less degradation due to artifacts) and T2w-MRCP (higher order of visualized branches, better branch depiction). Both readers showed preference for T2w-MRCP; however, both readers found gadoxetic acid-enhanced T1w-MRC helpful in the majority of cases.

CONCLUSION

Gadoxetic acid-enhanced T1w-MRC is complementary to, but should not replace, T2w-MRCP. T1w-MRC is a useful adjunct to T2w-MRCP for morphologic evaluation and provides additional diagnostic information.

MRI of the lumbar spine at 7 Tesla in healthy volunteers and a patient with congenital malformations

OBJECTIVE

The aim of this study was to evaluate sequences that are established at lower magnetic field strengths for lumbar spine imaging at 7 Tesla (7 T) MR imaging.

MATERIALS AND METHODS

The lumbar spine of five healthy volunteers and a patient with spina bifida and meningocele were evaluated at 7 T. The examination included a T2-TSE (turbo spin echo), a 3D-DESS (double-echo steady-state sequence), a 3D-CISS (constructive interference in steady-state sequence), and a 3D-VIBE (volumetric interpolated breath hold examination) sequence. Imaging quality was evaluated by two raters on a three-level scale. The assessment included visualization of intraforaminal structures, the cauda equina, facet joints, and any abnormalities. Contrast ratios for intervertebral discs/vertebral bodies, vertebral bodies/cerebrospinal fluid (CSF) and CSF/spinal cord were calculated.

RESULTS

The 3D-VIBE sequence provided best differentiation between intraforaminal structures. Visualization of the facet joints was reliable with VIBE, DESS, and CISS. Individual nerve roots of the cauda equina could only be delineated with the 3D-CISS sequence. CISS and DESS provided good contrast between vertebral bodies and intervertebral discs. Contrast between CSF and vertebral bodies was most pronounced for the T2-TSE sequence. Sufficient contrast between CSF and the spinal cord was only achieved with the T2-TSE sequence. VIBE and DESS sequences demonstrated best the bony malformations. Visualization of the meningocele was only possible with the 3D-CISS sequence.

CONCLUSION

At 7 T most structures of the lumbar spine were visualized with a combination of sequences. At present, imaging quality is not superior to 1.5 T or 3 T, precluding routine clinical use.

In-phase and out-of-phase gradient-echo imaging in abdominal studies: intra-individual comparison of three different techniques

BACKGROUND

T1-weighted gradient-echo in-phase and out-of-phase imaging is an essential component of comprehensive abdominal MR exams. It is useful for the study of fat-containing lesions and to identify various disease states related to the presence of fat in the liver.

PURPOSE

To compare three T1-weighted in-phase and out-of-phase (IP/OP) gradient-echo imaging sequences in an intra-individual fashion, and to determine whether advantages exist for each of these sequences for various patient types.

MATERIAL AND METHODS

One hundred and eighteen consecutive subjects (74 men, 44 women; mean age 53.9 ± 13.8 years) who had MRI examinations containing all three different IP/OP sequences (two-dimensional spoiled gradient-echo [2D-GRE], three-dimensional gradient-echo [3D-GRE], and magnetization-prepared gradient-recall echo [MP-GRE]) were included. Two different reviewers independently and blindly qualitatively evaluated IP/OP sequences to determine image quality, extent of artifacts, lesion detectability and conspicuity, and subjective grading of liver steatosis for the various sequences. Quantitative analysis was also performed. Qualitative and quantitative data were subjected to statistical analysis.

RESULTS

Respiratory ghosting, parallel imaging, and truncation artifacts as well as shading and blurring were more pronounced with 3D-GRE IP/OP imaging. Overall image quality was higher with 2D-GRE (P < 0.05). Detectability of low-fluid content lesions was lower with IP/OP MP-GRE sequences. MP-GRE sequences had the lowest SNRs (P < 0.001). Liver-to-spleen and liver-to-lesion CNRs were significantly lower with 3D-GRE and MP-GR, respectively (P < 0.001). Fat liver indexes showed strongly positive correlation between all sequences.

CONCLUSION

Currently, 2D-GRE remains the best approach for clinical IP/OP imaging. The good image quality of MP-GRE sequences acquired in a free-breathing manner should recommend its use in patients unable to suspend breathing.

Fast 3D contrast enhanced MRI of the liver using temporal resolution acceleration with constrained evolution reconstruction

Time-resolved imaging is crucial for the accurate diagnosis of liver lesions. Current contrast enhanced liver magnetic resonance imaging acquires a few phases in sequential breath-holds. The image quality is susceptible to bolus timing errors, which could result in missing the critical arterial phase. This impairs the detection of malignant tumors that are supplied primarily by the hepatic artery. In addition, the temporal resolution may be too low to reliably separate the arterial phase from the portal venous phase. In this study, a method called temporal resolution acceleration with constrained evolution reconstruction was developed with three-dimensional volume coverage and high-temporal frame rate. Data is acquired using a stack of spirals sampling trajectory combined with a golden ratio view order using an eight-channel coil array. Temporal frames are reconstructed from vastly undersampled data sets using a nonlinear inverse algorithm assuming that the temporal changes are small at short time intervals. Numerical and phantom experimental validation is presented. Preliminary in vivo results demonstrated high spatial resolution dynamic three-dimensional images of the whole liver with high frame rates, from which numerous subarterial phases could be easily identified retrospectively.

Evaluation of the inferior alveolar canal for cysts and tumors of the mandible-comparison of multidetector computed tomography and 3-dimensional volume interpolated breath-hold examination magnetic resonance sequence with curved multiplanar reformatted reconstructions

OBJECTIVE

To evaluate the mandibular canal using volume interpolated breath-hold examination (VIBE) sequencing in patients with cysts and tumors of the mandible.

MATERIALS AND METHODS

Twenty-five patients with mandibular cysts and tumors were recruited for a study in the authors' institution to compare the role of multidetector row computed tomography with magnetic resonance imaging (MRI) in jaw lesions. Of these 25 patients, VIBE was performed in 12 patients (age range, 16 to 52 yrs; 11 male and 1 female patients) and formed the study group. The status (normal/destroyed/attenuated) and position of the inferior alveolar canal (normal/displaced) on panoramic reconstructed computed tomographic (CT) images and curved multiplanar reformatted (MPR) images reconstructed from VIBE images were analyzed. The contralateral normal mandibular canal was used as the control in these patients.

RESULTS

In all 12 patients, the inferior alveolar canal on the normal side was visualized as a hyperintense structure in relation to the hypointense bone on the curved MPR VIBE images. In 9 patients, the inferior alveolar canal was equally well visualized on panoramic CT and curved MPR VIBE images. In 2 patients, the inferior alveolar canal was better visualized on curved MPR VIBE images; in 1 patient, the course of the mandibular canal was better seen on panoramic CT images.

CONCLUSIONS

MR reconstructions with VIBE sequencing as source images provide images comparable to CT reconstructed images for evaluation of the mandibular canal. Three-dimensional (3D) VIBE sequencing can be added to the MR protocol to visualize the inferior alveolar neurovascular bundle. 3D VIBE sequencing increases the diagnostic capabilities of MRI when used to image mandibular cysts and tumors.

ARFI-prepared MRgHIFU in liver: simultaneous mapping of ARFI-displacement and temperature elevation, using a fast GRE-EPI sequence

MR acoustic radiation force imaging (ARFI) is an elegant adjunct to MR-guided high intensity focused ultrasound for treatment planning and optimization, permitting in situ assessment of the focusing and targeting quality. The thermal effect of high intensity focused ultrasound pulses associated with ARFI measurements is recommended to be monitored on line, in particular when the beam crosses highly absorbent structures or interfaces (e.g., bones or air-filled cavities). A dedicated MR sequence is proposed here, derived from a segmented gradient echo-echo planar imaging kernel by adding a bipolar motion encoding gradient with interleaved alternating polarities. Temporal resolution was reduced to 2.1 s, with in-plane spatial resolution of 1 mm. MR-ARFI measurements were executed during controlled animal breathing, with trans-costal successively steered foci, to investigate the spatial modulation of the focus intensity and the targeting offset. ARFI-induced tissue displacement measurements enabled the accurate localization, in vivo, of the high intensity focused ultrasound focal point in sheep liver, with simultaneous monitoring of the temperature elevation. ARFI-based precalibration of the focal point position was immediately followed by trans-costal MR-guided high intensity focused ultrasound ablation, monitored with a conventional proton resonance frequency shift MR thermometry sequence. The latter MR thermometry sequence had spatial resolution and geometrical distortion identical with the ARFI maps, hence no coregistration was required.

Dynamic contrast-enhanced 3-T magnetic resonance imaging: a method for quantifying disease activity in early polyarthritis

OBJECTIVE

To determine whether measurement of synovial enhancement and thickness quantification parameters with 3.0-Tesla magnetic resonance imaging (3-T MRI) can reliably quantify disease activity in patients with early polyarthritis.

MATERIALS AND METHODS

Eighteen patients (16 women, 2 men; mean age 46 years) with early polyarthritis with less than 12 months of symptoms were included. MRI examination using 3-T device was performed by a new approach including both wrists and hands simultaneously in the examination field-of-view. MRI scoring of disease activity included quantification of synovial enhancement with simple measurements such as rate of early enhancement (REE; REE(57) = S(57)/S(200), where S(57) and S(200) are the signal intensities 57 s and 200 s after gadolinium injection) and rate of relative enhancement (RE; RE = S(200) - S(0)). Both wrists and hands were scored according to the Rheumatoid Arthritis MRI Scoring System (RAMRIS) for synovitis. Disease activity was clinically assessed by the 28-joint Disease Activity Score (DAS28).

RESULTS

DAS28 score was strongly correlated with RE (r = 0.8331, p < 0.0001), REE (r = 0.8112, p < 0.0001), and RAMRIS score for synovitis (r = 0.7659, p < 0.0002). An REE score above 0.778 accurately identified patients with clinically active disease (sensitivity 92%; specificity 67%; p < 0.05). A statistically significant difference was observed in the RE, REE, and RAMRIS scores for synovitis between patients with active and inactive disease (p < 0.05).

CONCLUSIONS

Our findings support the use of 3-T dynamic contrast-enhanced MRI for precise quantification of disease activity and for discriminating active disease from inactive disease in early polyarthritis.

Comparison between different implementations of the 3D FLASH sequence for knee cartilage quantification

OBJECTIVE

To compare several sequence implementations of the 3D FLASH sequence in the context of quantitative cartilage imaging.

MATERIALS AND METHODS

Test-retest coronal fast low angle shot (FLASH) sequences with water excitation were acquired in knees of 12 healthy participants, using two 1.5 T scanners from the same manufacturer. On one of the scanners, the FLASH was additionally compared with a FLASH VIBE, 75% with 100% slice resolution, a non-selective with a conventional spatial pulse, and "asymmetric echo allowed" with "not allowed".

RESULTS

Implementations of the FLASH showed systematic differences of up to 3.3%, but these were not statistically significant. Precision errors were similar between protocols, but tended to be smallest for the FLASH VIBE with 100% slice resolution (0.6-6.7%). In the medial tibia cartilage volume and thickness differed significantly (P < 0.01; 6.2 and 5.9%) between the two scanners.

CONCLUSION

Using a validated FLASH sequence, one can reduce slice resolution to 75% and allow asymmetric echo without sacrificing precision, in order to reduce the total acquisition time. However, in longitudinal studies, the scanner and the specific sequence implementation should be kept constant between baseline and follow-up, in order to avoid systematic off-sets in the measurements.

DCE-MRI of the human kidney using BLADE: a feasibility study in healthy volunteers

PURPOSE

To evaluate the degree of motion compensation in the kidney using two different sampling methods, each in their optimized settings: A BLADE k-space acquisition technique and a routinely used kidney perfusion acquisition scheme (TurboFLASH).

MATERIALS AND METHODS

Dynamic contrast enhanced magnetic resonance examinations were performed in 16 healthy volunteers on a 3 Tesla MR-system with two parameterizations of the BLADE sequence and the standard reference acquisition scheme. Signal intensity enhanced time curves were analyzed with a mathematical model and a widely published separable compartment model on cortex regions to assess robustness versus motion artifacts.

RESULTS

BLADE-measurements with a strip-width of 32 lines constituted the smallest mean values for the sum of squared errors (6065 ± 4996) compared with the measurement with a strip-width of 64 lines (13849 ± 14079) or the standard TurboFLASH (11884 ± 8076). Calculations concerning goodness of the fit of the applied compartment model yielded an overall average of the Akaike Fit Error of 732 ± 141 for BLADE (646 ± 149 for a strip-width of 32 lines, 816 ± 53 for 64 lines) and 1626 ± 303 for the TurboFLASH (TFL) sequence.

CONCLUSION

We demonstrated that renal dynamic contrast enhanced magnetic resonance imaging using BLADE k-space sampling with a strip-width of 32 is significantly less sensitive to motion than a widely published Turbo-Flash sequence with nearly similar parameters.

The value of 3D T1-weighted gradient-echo MR imaging for evaluation of the appendix during pregnancy: preliminary results

BACKGROUND

The use of oral contrast has been essential for the identification of a normal appendix on MR imaging during pregnancy. However, stool could be used as a positive oral contrast as it is characterized by a relatively high signal on T1-weighted imaging, and 3D T1-weighted gradient-echo (T1W-GRE) MR imaging has been used to evaluate 3 mm diameter intestines in fetuses.

PURPOSE

To evaluate the added value of 3D T1W-GRE MR imaging in combination with T2-weighted imaging (T2WI) compared to T2WI alone for evaluating the appendix during pregnancy.

MATERIAL AND METHODS

Eighteen consecutive pregnant patients who were clinically suspected of having acute appendicitis underwent appendix MR imaging which included T2WI with or without spectral presaturation attenuated inversion-recovery (SPAIR) fat suppression, and 3D T1W-GRE with SPAIR fat suppression. Two radiologists reviewed the two image sets (the T2WI set and the combined set of T2WI and 3D T1W-GRE images). Pathologic and clinical results served as the reference standard. The differences in the degree of visibility of the appendix and confidence scale for diagnosing acute appendicitis between two image sets were compared by using the paired Wilcoxon signed rank test.

RESULTS

For both reviewers, the degree of visibility of the appendix using the combined T2WI and 3D T1W-GRE images was significantly higher than using T2WI alone (P < 0.01), and the confidence levels for acute appendicitis using combined T2WI and 3D T1W-GRE images were significantly different from those using T2WI alone (P < 0.01). In the 13 patients with a normal appendix, both reviewers showed improved confidence levels for appendicitis using combined T2WI and 3D T1W-GRE images than T2WI alone.

CONCLUSION

Adding 3D T1W-GRE images to T2WI is helpful for identification of the appendix, as compared to T2WI alone in pregnant women without ingestion of oral contrast material. This may improve diagnostic confidence for acute appendicitis in pregnant patients.

Gadoxetic acid disodium-enhanced hepatocyte phase MRI: can increasing the flip angle improve focal liver lesion detection?

PURPOSE

To determine whether hepatocyte phase gadoxetic acid disodium (EOB)-enhanced MRI using a high flip angle (FA) improves focal liver lesion (FLL) detection compared with using a standard low FA.

MATERIALS AND METHODS

Sixty-two consecutive patients with 159 FLLs underwent EOB-enhanced MRI during the hepatocyte phase at 5, 10, 15, and 20 min, with both low (10°) and high (30°) FAs. Two blinded radiologists independently and randomly reviewed the two image sets using a four-point rating scale. Sensitivities and specificities were calculated and lesion-to-liver contrast ratio (LLC) on all hepatocyte phase images was measured.

RESULTS

The sensitivities with high FA for small (≤10 mm) malignant FLLs were significantly higher than those with low FA, at all time points, for both readers (P ≤ 0.05). Meanwhile, the specificities of the two protocols for the detection of all FLLs at all time points during the hepatocyte phase were high and same (98.2%) for both readers, without any significant differences (P = 1.00). LLCs with high FA were significantly higher than those with low FA at all time points (P ≤ 0.001).

CONCLUSION

Hepatocyte phase EOB-enhanced MRI with increasing FA can significantly increase LLC and improve the detection of FLLs, particularly small malignant lesions.

Pancreaticobiliary duct changes of periampullary carcinomas: quantitative analysis at MR imaging

PURPOSE

To quantitatively analyse the pancreaticobiliary duct changes of periampullary carcinomas with volumetric interpolated breath-hold examination (VIBE) and true fast imaging with steady-state precession (true FISP) sequence, and investigate the value of these findings in differentiation and preoperative evaluation.

MATERIALS AND METHODS

Magnetic resonance (MR) images of 71 cases of periampullary carcinomas (34 cases of pancreatic head carcinoma, 16 cases of intrapancreatic bile duct carcinoma and 21 cases of ampullary carcinoma) confirmed histopathologically were analysed. The maximum diameter of the common bile duct (CBD) and main pancreatic duct (MPD), dilated pancreaticobiliary duct angle and the distance from the end of the proximal dilated pancreaticobiliary duct to the major papilla were measured. Analysis of variance and the Chi-squared test were performed.

RESULTS

These findings showed significant differences among the three subtypes: the distance from the end of proximal dilated pancreaticobiliary duct to the major papilla and pancreaticobiliary duct angle. The distance and the pancreaticobiliary duct angle were least for ampullary carcinoma among the three subtypes. The percentage of dilated CBD was 94.1%, 93.8%, and 100% for pancreatic head carcinoma, intrapancreatic bile duct carcinoma and ampullary carcinoma, respectively. And that for the dilated MPD was 58.8%, 43.8%, and 42.9%, respectively.

CONCLUSION

Quantitative analysis of the pancreaticobiliary ductal system can provide accurate and objective assessment of the pancreaticobiliary duct changes. Although benefit in differential diagnosis is limited, these findings are valuable in preoperative evaluation for both radical resection and palliative surgery.

Image-based monitoring of magnetic resonance-guided thermoablative therapies for liver tumors

Minimally invasive treatment options for liver tumor therapy have been increasingly used during the last decade because their benefit has been proven for primary and inoperable secondary liver tumors. Among these, radiofrequency ablation has gained widespread consideration. Optimal image-guidance offers precise anatomical information, helps to position interventional devices, and allows for differentiation between already-treated and remaining tumor tissue. Patient safety and complete ablation of the entire tumor are the overriding objectives of tumor ablation. These may be achieved most elegantly with magnetic resonance (MR)-guided therapy, where monitoring can be performed based on precise soft-tissue imaging and additional components, such as diffusion-weighted imaging and temperature mapping. New MR scanner types and newly developed sequence techniques have enabled MR-guided intervention to move beyond the experimental phase. This article reviews the current role of MR imaging in guiding radiofrequency ablation. Signal characteristics of primary and secondary liver tumors are identified, and signal alteration during therapy is described. Diffusion-weighted imaging (DWI) and temperature mapping as special components of MR therapy monitoring are introduced. Practical information concerning coils, sequence selection, and parameters, as well as sequence gating, is given. In addition, sources of artifacts are identified and techniques to decrease them are introduced, and the characteristic signs of residual tumor in T1-, T2-, and DWI are described. We hope to enable the reader to choose MR sequences that allow optimal therapy monitoring depending on the initial signal characteristics of the tumor as well as its size and location in the liver.

Pragmatic study of orlistat 60 mg on abdominal obesity

BACKGROUND/OBJECTIVES

It is well established that combining a reduced calorie, low-fat diet with the lipase inhibitor orlistat results in significantly greater weight loss than placebo plus diet. This weight loss is accompanied by changes in adipose tissue (AT) distribution. As 60 mg orlistat is now available as an over-the-counter medication, the primary objective of this study was to determine whether 60 mg orlistat is effective as a weight loss option in a free-living community population with minimal professional input.

METHODS

AT and ectopic lipid content were measured using magnetic resonance imaging and (1)H MR spectroscopy, respectively, in 27 subjects following 3 months treatment with orlistat 60 mg and a reduced calorie, low-fat diet.

RESULTS

Significant reductions in intra-abdominal AT (-10.6%, P=0.023), subcutaneous (-11.7% P<0.0001) and pericardial fat (-9.8%, P=0.034) volumes and intrahepatocellular lipids (-43.3%, P=0.0003) were observed. These changes in body fat content and distribution were accompanied by improvements in plasma lipids and decreases in blood pressure and heart rate.

CONCLUSION

These findings suggest that over-the-counter 60 mg orlistat, in combination with the type of advice a subject could expect to be given when obtaining 60 mg orlistat in a community setting, does indeed result in potentially clinically beneficial changes in body composition and risk factors for metabolic diseases.

Additional value of gadoxetic acid-DTPA-enhanced hepatobiliary phase MR imaging in the diagnosis of early-stage hepatocellular carcinoma: comparison with dynamic triple-phase multidetector CT imaging

PURPOSE

To assess the value of hepatobiliary phase gadoxetic acid (EOB)-enhanced magnetic resonance imaging (MRI) for the diagnosis of early stage hepatocellular carcinoma (HCC) (<3 cm) compared to triple-phase dynamic multidetector computed tomography (MDCT).

MATERIALS AND METHODS

In all, 52 patients with 60 pathologically proven HCCs underwent both EOB-enhanced MRI and triple-phase dynamic MDCT. Two radiologists independently and blindly reviewed three image sets: 1) MDCT, 2) dynamic MRI (unenhanced and EOB-enhanced dynamic MR images), and 3) combined MRI (dynamic MRI + hepatobiliary phase images) using a five-point rating scale on a lesion-by-lesion basis. Receiver operating characteristics (ROC) analysis was performed, and sensitivity and specificity were calculated.

RESULTS

The area under the ROC curve (Az) of dynamic MRI was equivalent to that of MDCT for both readers. For both readers, Az and sensitivity of combined MRI for smaller lesions (<1.5 cm) were significantly higher than that of dynamic MRI and MDCT (P < 0.0166). The majority of false-negative nodules on dynamic MRI or MDCT (75% and 62%, respectively) were due to a lack of identified washout findings.

CONCLUSION

Hepatobiliary phase images can increase the value of EOB-enhanced MRI in the diagnosis of early stage HCC. The sensitivity and accuracy were significantly superior to MDCT for the diagnosis of lesions less than 1.5 cm.

Preclinical models for neuroblastoma: establishing a baseline for treatment

Background

Preclinical models of pediatric cancers are essential for testing new chemotherapeutic combinations for clinical trials. The most widely used genetic model for preclinical testing of neuroblastoma is the TH-MYCN mouse. This neuroblastoma-prone mouse recapitulates many of the features of human neuroblastoma. Limitations of this model include the low frequency of bone marrow metastasis, the lack of information on whether the gene expression patterns in this system parallels human neuroblastomas, the relatively slow rate of tumor formation and variability in tumor penetrance on different genetic backgrounds. As an alternative, preclinical studies are frequently performed using human cell lines xenografted into immunocompromised mice, either as flank implant or orthtotopically. Drawbacks of this system include the use of cell lines that have been in culture for years, the inappropriate microenvironment of the flank or difficult, time consuming surgery for orthotopic transplants and the absence of an intact immune system.

Principal Findings

Here we characterize and optimize both systems to increase their utility for preclinical studies. We show that TH-MYCN mice develop tumors in the paraspinal ganglia, but not in the adrenal, with cellular and gene expression patterns similar to human NB. In addition, we present a new ultrasound guided, minimally invasive orthotopic xenograft method. This injection technique is rapid, provides accurate targeting of the injected cells and leads to efficient engraftment. We also demonstrate that tumors can be detected, monitored and quantified prior to visualization using ultrasound, MRI and bioluminescence. Finally we develop and test a “standard of care” chemotherapy regimen. This protocol, which is based on current treatments for neuroblastoma, provides a baseline for comparison of new therapeutic agents.

Significance

The studies suggest that use of both the TH-NMYC model of neuroblastoma and the orthotopic xenograft model provide the optimal combination for testing new chemotherapies for this devastating childhood cancer.

Magnetic resonance imaging of the liver: sequence optimization and artifacts

The liver is one of the most challenging organs of the body to image with magnetic resonance because it is large and mobile, receives a dual blood supply, and is surrounded by organs and structures that contribute to artifacts from flow and susceptibility. Recent advances in imaging hardware, in addition to improvements in temporal resolution and development of hepatocyte-specific contrast agents, make imaging of the liver more approachable than in the past; however, it remains a complex process that requires compromise. In this article the authors discuss development and optimization of a liver imaging protocol at 1.5 T, with common variations in each element of the protocol, as well as the strengths and weaknesses associated with the relevant sequences.

Imaging at higher magnetic fields: 3 T versus 1.5 T

Clinical hepatobiliary magnetic resonance (MR) imaging continues to evolve at a fast rate. However, three basic requirements must still be satisfied if novel high-field MR imaging techniques are to be included in the hepatobiliary imaging routine: improvement of parenchymal contrast, suppression of respiratory motion artifact, and anatomic coverage of the entire hepatobiliary system. This article outlines the various arenas involved in MR imaging of the hepatobiliary system at 3 Tesla (T) compared with 1.5 T by (1) highlighting magnetic field-dependent MR contrast phenomena that contribute to the overall appearance of high-field hepatobiliary imaging; (2) summarizing the biodistributions of different gadolinium chelates used as MR contrast agents and their effectiveness regarding the static magnetic field; (3) showing the implementation of advanced imaging techniques such as three-dimensional acquisition schemes and parallel acceleration techniques used in T1-, T2-, and diffusion-weighted hepatobiliary imaging; and (4) addressing artifact mechanisms exacerbated by, or originating from, increase of the static magnetic field.

Hepatic MR imaging for in vivo differentiation of steatosis, iron deposition and combined storage disorder: single-ratio in/opposed phase analysis vs. dual-ratio Dixon discrimination

OBJECTIVE

To assess whether in vivo dual-ratio Dixon discrimination can improve detection of diffuse liver disease, specifically steatosis, iron deposition and combined disease over traditional single-ratio in/opposed phase analysis.

METHODS

Seventy-one patients with biopsy-proven (17.7 ± 17.0 days) hepatic steatosis (n = 16), iron deposition (n = 11), combined deposition (n = 3) and neither disease (n = 41) underwent MR examinations. Dual-echo in/opposed-phase MR with Dixon water/fat reconstructions were acquired. Analysis consisted of: (a) single-ratio hepatic region-of-interest (ROI)-based assessment of in/opposed ratios; (b) dual-ratio hepatic ROI assessment of in/opposed and fat/water ratios; (c) computer-aided dual-ratio assessment evaluating all hepatic voxels. Disease-specific thresholds were determined; statistical analyses assessed disease-dependent voxel ratios, based on single-ratio (a) and dual-ratio (b and c) techniques.

RESULTS

Single-ratio discrimination succeeded in identifying iron deposition (I/O(Ironthreshold)<0.88) and steatosis (I/O(Fatthreshold>1.15)) from normal parenchyma, sensitivity 70.0%; it failed to detect combined disease. Dual-ratio discrimination succeeded in identifying abnormal hepatic parenchyma (F/W(Normalthreshold)>0.05), sensitivity 96.7%; logarithmic functions for iron deposition (I/O(Irondiscriminator)<e((0.01-F/W(Iron))/0.48)) and for steatosis (I/O(Fatdiscriminator)>e((F/W(Fat)-0.01)/0.48)) differentiated combined from isolated diseases, sensitivity 100.0%; computer-aided dual-ratio analysis was comparably sensitive but less specific, 90.2% vs. 97.6%.

CONCLUSION

MR two-point-Dixon imaging using dual-ratio post-processing based on in/opposed and fat/water ratios improved in vivo detection of hepatic steatosis, iron deposition, and combined storage disease beyond traditional in/opposed analysis.

T(2)-weighted 3D fast spin echo imaging with water-fat separation in a single acquisition

PURPOSE

To develop a robust 3D fast spin echo (FSE) T(2)-weighted imaging method with uniform water and fat separation in a single acquisition, amenable to high-quality multiplanar reformations.

MATERIALS AND METHODS

The Iterative Decomposition of water and fat with Echo Asymmetry and Least squares estimation (IDEAL) method was integrated with modulated refocusing flip angle 3D-FSE. Echoes required for IDEAL processing were acquired by shifting the readout gradient with respect to the Carr-Purcell-Meiboom-Gill echo. To reduce the scan time, an alternative data acquisition using two gradient echoes per repetition was implemented. Using the latter approach, a total of four gradient echoes were acquired in two repetitions and used in the modified IDEAL reconstruction.

RESULTS

3D-FSE T(2)-weighted images with uniform water-fat separation were successfully acquired in various anatomies including breast, abdomen, knee, and ankle in clinically feasible scan times, ranging from 5:30-8:30 minutes. Using water-only and fat-only images, in-phase and out-of-phase images were reconstructed.

CONCLUSION

3D-FSE-IDEAL provides volumetric T(2)-weighted images with uniform water and fat separation in a single acquisition. High-resolution images with multiple contrasts can be reformatted to any orientation from a single acquisition. This could potentially replace 2D-FSE acquisitions with and without fat suppression and in multiple planes, thus improving overall imaging efficiency.

Optimization of single injection liver arterial phase gadolinium enhanced MRI using bolus track real-time imaging

PURPOSE

To measure contrast agent enhancement kinetics in the liver and to further evaluate and develop an optimized gadolinium enhanced MRI using a single injection real-time bolus-tracking method for reproducible imaging of the transient arterial-phase.

MATERIALS AND METHODS

A total of 18 subjects with hypervascular liver lesions were imaged with four dimensional (4D) perfusion scans to measure time-to-peak (TTP) delays of arterial (aorta-celiac axis), liver parenchyma, liver lesion, portal, and hepatic veins. Time delays were calculated from the TTP-aorta signal, and then related to the gradient echo (GRE) k-space acquisition design, to determine optimized timing for real-time bolus-track triggering methodology. As another measure of significance, 200 clinical patients were imaged with 3D-GRE using either a fixed time-interval or by individualized arterial bolus real-time triggering. Bolus TTP-aorta was calculated and arterial-phase acquisitions were compared for accuracy and reproducibility using specific vascular enhancement indicators.

RESULTS

The mean bolus transit-time to peak-lesion contrast was 8.1 ± 2.7 seconds following arterial detection, compared to 32.1 ± 5.4 seconds from contrast injection, representing a 62.1% reduction in the time-variability among subjects (N = 18). The real-time bolus-triggered technique more consistently captured the targeted arterial phase (94%), compared to the fixed timing technique (73%), representing an expected improvement of timing accuracy in 28% of patients (P = 0.0001389).

CONCLUSION

Our results show detailed timing window analysis required for optimized arterial real-time bolus-triggering acquisition of transient arterial phase features of liver lesions, with optimized arterial triggering expected to improve reproducibility in a significant number of patients.

Comparison of portal venous and delayed phases of gadolinium-enhanced magnetic resonance imaging study of cirrhotic liver for the detection of contrast washout of hypervascular hepatocellular carcinoma

OBJECTIVE

To retrospectively compare portal venous phase (PVP) and delayed phase (DP) for the detection of tumor washout at gadobenate dimeglumine-enhanced liver magnetic resonance imaging (MRI) in cirrhotic patients with hypervascular hepatocellular carcinoma (HCC).

METHODS

Thirty-three patients with 55 HCCs underwent 1.5-T MRI by means of fat-suppressed T1-weighted sequence obtained before and after gadobenate dimeglumine administration, during early and late arterial phases, PVP (70 seconds), and DP (180 seconds). Detection rates of contrast washout of hypervascular HCCs and tumor-to-liver contrast on PVP and DP were measured and compared.

RESULTS

Among 54 hypervascular HCCs, washout was present in 24 (44%) of 54 tumors on PVP and in 44 (82%) of 54 on DP (P < 0.001). In 20 (37%) of 54 tumors, washout was deemed present only on DP. Delayed phase images yielded significantly higher mean tumor-to-liver contrast absolute values compared with PVP images (-24.5 [56.1] vs -9.3 [52.6], P = 0.001).

CONCLUSIONS

Delayed phase is superior to PVP for the washout detection of hypervascular HCC at gadobenate dimeglumine-enhanced MRI of cirrhotic liver.

[Whole body functional MR imaging: hemato-oncologic applications]

Hemato-oncologic imaging combines anatomical and functional imaging data for optimal staging and follow-up of patients. It is currently possible to achieve high spatial resolution and functional evaluation at whole body MR imaging. Functional imaging may be achieved with two techniques: dynamic imaging following intravenous contrast injection and diffusion-weighted imaging. The purpose of this article is to demonstrate how both functional imaging techniques can be combined with whole body MR imaging for the evaluation of multiple myeloma and lymphomas.

Pretreatment assessment of hepatocellular carcinoma: expert consensus statement

Staging of hepatocellular carcinoma (HCC) is complex and relies on multiple factors including tumor extent and hepatic function. No single staging system is applicable to all patients with HCC. The staging of the American Joint Committee on Cancer / International Union for Cancer Control should be used to predict outcome following resection or liver transplantation. The Barcelona Clinic Liver Cancer scheme is appropriate in patients with advanced HCC not candidate for surgery. Dual phase computed tomography or magnetic resonance imaging can be used for pretreatment assessment of tumor extent but the accuracy of these methods remains poor to characterize < 1 cm lesions. Assessment of tumor response should not rely only on tumor size and new imaging methods are available to evaluate response to therapy in HCC patients. Liver volumetry is part of the preoperative assessment of patients with HCC candidate for resection as it reflects liver function. Preoperative portal vein embolization is indicated in patients with small future liver remnant (≤ 20% in normal liver; ≤ 40% in fibrotic or cirrhotic liver). Tumor size is not a contraindication to liver resection. Liver resection can be proposed in selected patients with multifocal HCC. Besides tumor extent, surgical resection of HCC may be performed in selected patients with chronic liver disease.