Andrew D. Hardie

Diagnosis of liver metastases: value of diffusion-weighted MRI compared with gadolinium-enhanced MRI.

ObjectiveThe full diagnostic value of diffusion-weighted (DW) MRI in the evaluation of liver metastases remains uncertain. The aim of the present study was to assess the diagnostic accuracy of DW-MRI and contrast-enhanced MRI (CE-MRI) using extracellular gadolinium chelates, with the reference standard established by consensus interpretation of confirmatory imaging and histopathologic data.MethodsMR examinations of 51 patients with extrahepatic malignancies were retrospectively reviewed by two independent observers who assessed DW-MRI and CE-MRI for detection of liver metastases.ResultsBy reference standard, 93 liver lesions (49 metastases and 44 benign lesions) were identified in 27 patients, 11 patients had no liver lesions, and 13 patients had innumerable metastatic and/or benign lesions. There was no difference in diagnostic performance between the two methods for either observer for the diagnosis of metastatic lesions per patient. For per-lesion analysis, sensitivity of DW-MRI was equivalent to CE-MRI for observer 1 (67.3% vs. 63.3%, p = 0.67), but lower for observer 2 (65.3% vs. 83.7%, p = 0.007). By pooling data from both observers, the sensitivity of DW-MRI was 66.3% (65/98) and 73.5% (72/98) for CE-MRI, with no significant difference (p = 0.171).ConclusionDW-MRI is a reasonable alternative to CE-MRI for the detection of liver metastases.

Composition of the Stable Carotid Plaque Insights From a Multidetector Computed Tomography Study of Plaque Volume

Background and Purpose— Calcification has been associated with carotid plaque stability; however, an acceptable in vivo method to define plaques based on this component remains to be developed. The purpose of our study was to compare calcified and noncalcified volumes of carotid artery culprit symptomatic plaques with asymptomatic plaques using multidetector computed tomography. Methods— We identified 102 patients with ≥50% stenosis using NASCET criteria by multidetector computed tomography angiography between January 2004 and May 2006, which included 35 symptomatic (stenosis: 82.0±11.9%) and 67 asymptomatic patients (stenosis: 79.4±10.8%). Total plaque volume, noncalcified plaque volume, calcified plaque volume, and calcified/total ratio were measured for the 102 index plaques causing stenosis. Results— In a model including age, stenosis, and cardiovascular risk factors, calcified plaque volume/total plaque volume was significantly inversely associated with the occurrence of symptoms (P=0.012; odds ratio, 0.047; 95% CI, 0.004 to 0.511). There was a notable overlap in the calcified plaque volume/total plaque volume ratio between 0% and 45% for symptomatic and asymptomatic plaques. However, calcification >45% of the total plaque was very specific: 97.1% (34/35) for absence of symptoms (sensitivity: 28.4% 19/67). No significant association between total plaque volume, noncalcified plaque volume, or calcified plaque volume and symptomatology was found. Conclusion— The proportion of carotid plaque calcification, rather than absolute volume, is associated with stability in patients with stenosis. Specifically, for a subset of patients, plaque calcification >45% of the total volume may represent a clinically useful cutoff. The carotid plaque calcium ratio, determined by multidetector computed tomography volume measurements, may help noninvasively risk stratify patients with asymptomatic stenosis.

The Impact of Expansive Arterial Remodeling on Clinical Presentation in Carotid Artery Disease: A Multidetector CT Angiography Study

BACKGROUND AND PURPOSE: Atherosclerotic arterial remodeling has been described in the coronary circulation but has not been studied extensively for carotid atherosclerosis. The purpose of our study was to examine the association between carotid artery remodeling and clinical presentation in patients with significant stenosis by using multidetector row CT (MDCT). MATERIALS AND METHODS: One hundred eight patients with ≥50% stenosis (North American Symptomatic Carotid Endarterectomy Trial criteria) by MDCT angiography between January 2004 and June 2006 were identified. The study group included 37 symptomatic (65.9 ± 13.0 years; 12 women; stenosis, 81.5 ± 12.2%; 17 with stroke; 15 with transient ischemic attack; 5 with amaurosis fugax) and 71 asymptomatic patients (70.5 ± 10.5 years; 28 women; stenosis, 78.8 ± 11.1%). Remodeling ratio (RR) was calculated by dividing the outer vessel circumference at the site of greatest stenosis by a normal reference-segment vessel circumference. Maximum vessel thickness (MxVT) and eccentricity index (EI) of the plaque, defined as maximal thickness/minimal thickness at the site of greatest luminal narrowing, were also determined. Data were analyzed by using an independent t test. RESULTS: The RR was significantly higher in symptomatic patients (1.64 ± 0.44) than in asymptomatic patients (1.41 ± 0.5) (P=.02). There was no significant difference in MxVT in symptomatic (5.9 ± 2.1 mm) and asymptomatic patients (5.6 ± 2.4 mm) (P=.45) and no significant difference in EI (symptomatic, 4.7 ± 2.7; asymptomatic, 4.3 ± 2.2; P=.38). CONCLUSION: In this series of subjects with significant internal carotid artery stenosis, expansive carotid remodeling was significantly greater in patients with cerebral ischemic symptoms than in asymptomatic patients. The extent of expansive remodeling may indicate underlying atherosclerotic plaque vulnerability. MDCT has a role in the evaluation of carotid artery disease beyond examining luminal stenosis.

Dual-energy CT of the pancreas: improved carcinoma-to-pancreas contrast with a noise-optimized monoenergetic reconstruction algorithm

PURPOSE To evaluate a novel monoenergetic reconstruction algorithm (nMERA) with improved noise reduction for dual-energy CT (DECT) of pancreatic adenocarcinoma. MATERIALS AND METHODS Sixty patients with suspected pancreatic carcinoma underwent dual-source dual-energy CT with arterial phase. Images were reconstructed as linearly-blended 120-kV series (M_0.6) and with the standard monoenergetic (sMERA) and the novel monoenergetic algorithm (nMERA) with photon energies of 40, 55, 70 and 80 keV. Objective image quality was compared regarding image noise, pancreas attenuation, signal-to-noise ratio (SNR) and pancreas-to-lesion contrast. Subjective image quality was assessed by two observers. RESULTS Thirty pancreatic adenocarcinomas were detected. nMERA showed significantly reduced image noise at low keV levels compared with sMERA images (55 keV: 7.19 ± 2.75 vs. 20.68 ± 7.01 HU; 40 keV: 7.33 ± 3.20 vs. 37.22 ± 14.66 HU) and M_0.6 (10.69 ± 3.57 HU). nMERA pancreatic SNR was significantly superior to standard monoenergetic at 40 (47.02 ± 23.41 vs. 9.37 ± 5.83) and 55 keV (28.29 ± 16.86 vs. 9.88 ± 7.01), and M_0.6 series (11.42 ± 6.00). Pancreas-to-lesion contrast peaked in the nMERA 40 keV series (26.39 ± 16.83) and was significantly higher than in all other series (p<0.001). nMERA 55 keV images series were consistently preferred by both observers over all other series (p<0.01). CONCLUSIONS nMERA DECT can significantly improve image quality and pancreas-to-lesion contrast in the diagnosis of pancreatic adenocarcinoma.

Utility of quantitative MRI metrics for assessment of stage and grade of urothelial carcinoma of the bladder: preliminary results.

OBJECTIVE The purpose of this study was to assess associations between quantitative MRI metrics and pathologic indicators of aggressiveness of urothelial carcinoma of the bladder. MATERIALS AND METHODS In this retrospective biinstitutional study, 37 patients (28 men and nine women; mean age, 73 ± 12 years) who underwent pelvic MRI including diffusion-weighted imaging (b values 0, 400, and 800 s/mm(2)) and T2-weighted imaging before transurethral resection or cystectomy for urothelial carcinoma of the bladder were identified. Tumor diameter (measured on T2-weighted imaging), normalized T2 signal intensity (to muscle; hereafter labeled normalized T2) and apparent diffusion coefficient (ADC) were measured for all tumors. Mann-Whitney test and receiver operating characteristic analyses were used to identify associations between these metrics and histopathologic tumor stage and grade. RESULTS Thirty-seven tumors were assessed (mean size, 35 ± 23 mm; range 8-88 mm). At histopathologic analysis, 16 of 37 (43%) tumors were stage T2 or greater and 21 of 37 (57%) were stage T1 or lower, whereas 34 of 37 (92%) were high grade and three of 37 (8%) were low grade. High-stage (≥ T2) tumors showed greater tumor diameter, lower normalized T2, and lower ADC (p = 0.005-0.032) than low-stage (≤ T1) tumors. Tumor diameter and ADC were significant independent predictors of stage (p ≤ 0.043), with their combination giving an area-under the-curve (AUC) of 0.804. High-grade tumors showed significantly lower ADC (p = 0.023) but no significant difference in tumor diameter or normalized T2 (p = 0.201-0.559). AUC for differentiating low- and high-grade tumors was higher for ADC (0.902) than for tumor diameter (0.603) or normalized T2 (0.725). CONCLUSION A combination of size and quantitative MRI metrics can potentially be used as markers of stage and grade of bladder cancer.

Characterization of Adrenal Pheochromocytoma Using Respiratory-Triggered Proton MR Spectroscopy : Initial Experience

OBJECTIVE The aim of our study was to evaluate the feasibility of respiratory-triggered proton single-voxel MR spectroscopy for the diagnosis of adrenal pheochromocytoma and to determine whether certain spectral resonances detected on single-voxel MR spectroscopy are specific for adrenal pheochromocytomas compared with adrenal adenomas. CONCLUSION Adrenal pheochromocytomas have a unique MR spectral signature, showing 6.8 ppm resonance that is not seen in adenomas. This unique spectral signature may be attributed to the presence of catecholamines and catecholamine metabolites that are abundant in pheochromocytomas.

Application of an Advanced Image-Based Virtual Monoenergetic Reconstruction of Dual Source Dual-Energy CT Data at Low keV Increases Image Quality for Routine Pancreas Imaging.

Purpose To compare image quality on contrast-enhanced dual-energy computed tomography (DECT) during the pancreatic parenchymal phase of pancreatic masses between linearly-blended simulated 120 kVp images (routine) and advanced image-based virtual monoenergetic reconstructions at 55 keV. Methods This was a retrospective evaluation of 24 nonconsecutive adults found to have a focal pancreatic mass on a multiphasic abdominal dual-source DECT (12 adenocarcinoma, 5 neuroendocrine, 7 cystic tumors). For pancreatic-parenchymal phase images, subjects had routine and 55 keV images reconstructed at the time of clinical evaluation. Quantitative evaluation by contrast-to-noise ratio and qualitative evaluations of image quality by (1) direct comparison of image pairs (preference) and (2) blinded assessment of image quality measures based on Likert scores were performed. Results Mean patient weight was 205.8 ± 26.6 lbs. Mean pancreatic lesion contrast-to-noise ratio was significantly higher at 55 keV (6.8 ± 4.1) compared to the routine image series (5.8 ± 3.8; P = 0.0002). All 3 readers preferred the 55-keV images over routine blended images in 70.1% to 95.8% of cases. No significant differences were observed for subjective sharpness of the mass, visualization of internal mass structures, or image noise. Conclusions Use of a single advanced image-based virtual monoenergetic reconstruction at 55 keV in pancreatic DECT showed improved objective image quality and reader preference compared to routine images. As this image reconstruction can be incorporated into the scan protocol, this technique should be considered for routine clinical use.

Diagnostic accuracy of diffusion-weighted MRI for identifying hepatocellular carcinoma with liver explant correlation

Background: The goal of this study was to use liver explant correlation to assess the diagnostic accuracy of diffusion‐weighted (DW)‐MRI for hepatocellular carcinoma (HCC).

Optimization of window settings for virtual monoenergetic imaging in dual-energy CT of the liver: A multi-reader evaluation of standard monoenergetic and advanced imaged-based monoenergetic datasets.

OBJECTIVES To evaluate optimal window settings for display of virtual monoenergetic reconstructions in third-generation dual-source, dual-energy computed tomography (DECT) of the liver. METHODS Twenty-nine subjects were prospectively evaluated with DECT in arterial (AP) and portal venous (PVP) phases. Three reconstructed datasets were calculated: standard linearly-blended (LB120), 70-keV standard virtual monoenergetic (M70), and 50-keV advanced image-based virtual monoenergetic (M50+). Two readers assessed optimal window settings (width and level, W/L), establishing a mean for each reconstruction which was used for a blinded assessment of liver lesions. RESULTS The optimal W/L for M50+ were significantly higher for both AP (W=429.3 ± 44.6 HU, L=129.4 ± 9.7 HU) and PVP (W=376.1 ± 14.2HU, L=146.6 ± 7.0 HU) than for LB120 (AP, W=215.9 ± 16.9 HU, L=82.3 ± 9.4 HU) (PVP, W=173.4 ± 8.9 HU, L=69.3 ± 6.0 HU) and M70 (AP, W=247.1 ± 22.2 HU, L=72.9 ± 6.8 HU) (PVP, W=232.0 ± 27.9 HU, L=91.6 ± 14.4 HU). Use of the optimal window setting for M50+ vs. LB120 resulted in higher sensitivity (AP, 100% vs. 86%; PVP, 96% vs. 63%). CONCLUSIONS Application of dedicated window settings results in improved liver lesion detection rates in advanced image-based virtual monoenergetic DECT when customized for arterial and portal venous phases.

Can the patient with cirrhosis be imaged for hepatocellular carcinoma without gadolinium?: Comparison of combined T2-weighted, T2*-weighted, and diffusion-weighted MRI with gadolinium-enhanced MRI using liver explantation standard.

Purpose This study aimed to evaluate a non–gadolinium-enhanced magnetic resonance imaging (MRI) protocol including T2-weighted, T2*-weighted, and diffusion-weighted MRI sequences for identifying hepatocellular carcinoma (HCC) with liver explantation as the reference standard. Also, a stand-alone pre– and dynamic post–gadolinium-enhanced liver MRI data set was interpreted from the available patient data for relative comparison purposes. Materials and Methods A retrospective review identified 37 appropriately selected liver transplant patients who had had preoperative MRI. Two data sets were created from the MRI studies: (1) non–gadolinium-enhanced (including T2-weighted, T2*-weighted, and diffusion-weighted sequences) and (2) pre– and dynamic post–gadolinium-enhanced (3-dimensional T1-weighted gradient recalled echo) and were presented to 2 independent, blinded observers. A separate blinded observer assessed the pathologic results from liver explantation to establish the reference standard. Results On explant pathology, 21 of 37 patients had 31 HCC (mean [SD] largest diameter, 19 [9] cm; range, 7–40 mm). Per-lesion sensitivity of non–gadolinium-enhanced MRI for identifying HCC was 52% (reader 1) and 55% (reader 2), and specificity was 90% (reader 1) and 88% (reader 2). Per-lesion sensitivity of the stand-alone pre– and dynamic post–gadolinium-enhanced MRI was 84% (reader 1) and 81% (reader 2), and specificity was 62% (reader 1) and 65% (reader 2). Conclusions Non–gadolinium-enhanced MRI had a moderate sensitivity for HCC but had a high specificity. Although non–gadolinium-enhanced MRI cannot be recommended as a primary imaging approach for HCC, the results demonstrate the contribution of non–gadolinium-enhanced sequences to imaging of HCC. A non–gadolinium-enhanced MRI protocol may have a diagnostic value when gadolinium cannot be administered.