Meghan G. Lubner

Abdominal CT With Model-Based Iterative Reconstruction (MBIR): Initial Results of a Prospective Trial Comparing Ultralow-Dose With Standard-Dose Imaging

OBJECTIVE The purpose of this study was to report preliminary results of an ongoing prospective trial of ultralow-dose abdominal MDCT. SUBJECTS AND METHODS Imaging with standard-dose contrast-enhanced (n = 21) and unenhanced (n = 24) clinical abdominal MDCT protocols was immediately followed by ultralow-dose imaging of a matched series of 45 consecutively registered adults (mean age, 57.9 years; mean body mass index, 28.5). The ultralow-dose images were reconstructed with filtered back projection (FBP), adaptive statistical iterative reconstruction (ASIR), and model-based iterative reconstruction (MBIR). Standard-dose series were reconstructed with FBP (reference standard). Image noise was measured at multiple predefined sites. Two blinded abdominal radiologists interpreted randomly presented ultralow-dose images for multilevel subjective image quality (5-point scale) and depiction of organ-based focal lesions. RESULTS Mean dose reduction relative to the standard series was 74% (median, 78%; range, 57-88%; mean effective dose, 1.90 mSv). Mean multiorgan image noise for low-dose MBIR was 14.7 ± 2.6 HU, significantly lower than standard-dose FBP (28.9 ± 9.9 HU), low-dose FBP (59.2 ± 23.3 HU), and ASIR (45.6 ± 14.1 HU) (p < 0.001). The mean subjective image quality score for low-dose MBIR (3.0 ± 0.5) was significantly higher than for low-dose FBP (1.6 ± 0.7) and ASIR (1.8 ± 0.7) (p < 0.001). Readers identified 213 focal noncalcific lesions with standard-dose FBP. Pooled lesion detection was higher for low-dose MBIR (79.3% [169/213]) compared with low-dose FBP (66.2% [141/213]) and ASIR (62.0% [132/213]) (p < 0.05). CONCLUSION MBIR shows great potential for substantially reducing radiation doses at routine abdominal CT. Both FBP and ASIR are limited in this regard owing to reduced image quality and diagnostic capability. Further investigation is needed to determine the optimal dose level for MBIR that maintains adequate diagnostic performance. In general, objective and subjective image quality measurements do not necessarily correlate with diagnostic performance at ultralow-dose CT.

Inflammatory Pseudotumor: The Great Mimicker

OBJECTIVE The purpose of this review is to describe the pathophysiologic findings, differential diagnosis, imaging features, and management of inflammatory pseudotumor in various locations throughout the body. CONCLUSION Inflammatory pseudotumor is a rare benign process mimicking malignant processes and has been found in almost every organ system. Radiologists should be familiar with this entity as a diagnostic consideration to avoid unnecessary surgery.

Hepatobiliary MR imaging with gadolinium-based contrast agents

The advent of gadolinium‐based “hepatobiliary” contrast agents offers new opportunities for diagnostic magnetic resonance imaging (MRI) and has triggered great interest for innovative imaging approaches to the liver and bile ducts. In this review article we discuss the imaging properties of the two gadolinium‐based hepatobiliary contrast agents currently available in the U.S., gadobenate dimeglumine and gadoxetic acid, as well as important pharmacokinetic differences that affect their diagnostic performance. We review potential applications, protocol optimization strategies, as well as diagnostic pitfalls. A variety of illustrative case examples will be used to demonstrate the role of these agents in detection and characterization of liver lesions as well as for imaging the biliary system. Changes in MR protocols geared toward optimizing workflow and imaging quality are also discussed. It is our aim that the information provided in this article will facilitate the optimal utilization of these agents and will stimulate the readers pursuit of new applications for future benefit. J. Magn. Reson. Imaging 2012;35:492‐511.

Percutaneous Tumor Ablation Tools: Microwave, Radiofrequency, or Cryoablation—What Should You Use and Why?

Image-guided thermal ablation is an evolving and growing treatment option for patients with malignant disease of multiple organ systems. Treatment indications have been expanding to include benign tumors as well. Specifically, the most prevalent indications to date have been in the liver (primary and metastatic disease, as well as benign tumors such as hemangiomas and adenomas), kidney (primarily renal cell carcinoma, but also benign tumors such as angiomyolipomas and oncocytomas), lung (primary and metastatic disease), and soft tissue and/or bone (primarily metastatic disease and osteoid osteomas). Each organ system has different underlying tissue characteristics, which can have profound effects on the resulting thermal changes and ablation zone. Understanding these issues is important for optimizing clinical results. In addition, thermal ablation technology has evolved rapidly during the past several decades, with substantial technical and procedural improvements that can help improve clinical outcomes and safety profiles. Staying up to date on these developments is challenging but critical because the physical properties underlying the different ablation modalities and the appropriate use of adjuncts will have a tremendous effect on treatment results. Ultimately, combining an understanding of the physical properties of the ablation modalities with an understanding of the thermal kinetics in tissue and using the most appropriate ablation modality for each patient are key to optimizing clinical outcomes. Suggested algorithms are described that will help physicians choose among the various ablation modalities for individual patients.

Reduced Image Noise at Low-Dose Multidetector CT of the Abdomen with Prior Image Constrained Compressed Sensing Algorithm

PURPOSE To assess the effect of prior image constrained compressed sensing (PICCS) on noise reduction and image quality at low-dose computed tomography (CT). MATERIALS AND METHODS This HIPAA-compliant institutional review board-approved retrospective study was performed by using DICOM CT colonography data sets obtained in 20 adult patients. Informed consent was waived. Low-dose CT colonography was performed with 64-detector CT by using the standard protocol with mean effective dose per series of 3.06 mSv (range, 1.4-7.7 mSv). PICCS was applied to standard filtered back-projection (FBP) series. For FBP and PICCS series, mean and standard deviation (SD) of attenuation were obtained with 100-mm(2) circular region of interest (ROI) at six sites (240 soft-tissue, colonic gas, and subcutaneous fat measurements). Two abdominal radiologists reviewed two- and three-dimensional CT colonography displays and graded image quality with a five-point scale. Phantom studies were performed to compare spatial resolution and image quality between FBP and PICCS. Mean image noise and image quality scores were calculated and compared for clinical and phantom data sets. Bland-Altman, generalized estimating equation regression model, and Student t tests were used to obtain limits of agreement and to compare noise ratios and subjective image quality. RESULTS Mean SD of attenuation (image noise) for ROIs was 38.0 for FBP and 12.2 for PICCS, corresponding to a noise-reduction factor of 3.1 (P < .001). Average noise reduction was 3.3 for soft tissue, 2.8 for air, and 3.0 for fat attenuation. Attenuation did not substantially change between FBP and PICCS images. Average two-dimensional image quality was 2.45 for FBP and 3.4 for PICCS (P < .001). Average three-dimensional image quality at three sites in the colon was 3.5 for FBP and 3.7 for PICCS (P = .34). Phantom data sets revealed no loss of spatial resolution in a line phantom and reduced noise in a liver tumor phantom when PICCS was compared with FBP. CONCLUSION Application of PICCS to standard FBP low-dose multidetector CT abdominal images results in substantial noise reduction and improved image quality.

Visceral obesity is associated with outcomes of total mesorectal excision for rectal adenocarcinoma

General obesity, measured by the body mass index (BMI), increases the technical difficulty of total mesorectal excision (TME) but does not affect oncologic outcomes. The purpose of this study is to compare visceral and general obesity as predictors of outcomes of TME for rectal adenocarcinoma.

Microwave Ablation of Hepatic Malignancy

Microwave ablation is an extremely promising heat-based thermal ablation modality that has particular applicability in treating hepatic malignancies. Microwaves can generate very high temperatures in very short time periods, potentially leading to improved treatment efficiency and larger ablation zones. As the available technology continues to improve, microwave ablation is emerging as a valuable alternative to radiofrequency ablation in the treatment of hepatic malignancies. This article reviews the current state of microwave ablation including technical and clinical considerations.

Thermal Ablation of Lung Tumors

The 5-year survival for all stages of nonsmall cell lung cancer (NSCLC) remains bleak, having increased from 13% to just 16% over the past 30 years. Despite promising results in nonoperative patients with NSCLC and pulmonary metastatic disease, thermal ablation appears to be limited by large tumor size and proximity to large vessels. This article discusses the particular challenges of performing thermal ablation in aerated lung tissue and reviews important considerations in performing ablation including treatment complications and imaging follow-up. The article compares and contrasts the three major thermal ablation modalities: radiofrequency ablation, microwave ablation, and cryoablation.

Early Small-Bowel Ischemia: Dual-Energy CT Improves Conspicuity Compared with Conventional CT in a Swine Model

PURPOSE To compare dual-energy computed tomography (CT) with conventional CT for the detection of small-bowel ischemia in an experimental animal model. MATERIALS AND METHODS The study was approved by the animal care and use committee and was performed in accordance with the Guide for Care and Use of Laboratory Animals issued by the National Research Council. Ischemic bowel segments (n = 8) were created in swine (n = 4) by means of surgical occlusion of distal mesenteric arteries and veins. Contrast material-enhanced dual-energy CT and conventional single-energy CT (120 kVp) sequences were performed during the portal venous phase with a single-source fast-switching dual-energy CT scanner. Attenuation values and contrast-to-noise ratios of ischemic and perfused segments on iodine material-density, monospectral dual-energy CT (51 keV, 65 keV, and 70 keV), and conventional 120-kVp CT images were compared. Linear mixed-effects models were used for comparisons. RESULTS The attenuation difference between ischemic and perfused segments was significantly greater on dual-energy 51-keV CT images than on conventional 120-kVp CT images (mean difference, 91.7 HU vs 47.6 HU; P < .0001). Conspicuity of ischemic segments was significantly greater on dual-energy iodine material-density and 51-keV CT images than on 120-kVp CT images (mean contrast-to-noise ratios, 4.9, 4.3, and 2.1, respectively; P < .0001). Although attenuation differences on dual-energy 65- and 70-keV CT images were not significantly different from those on 120-kVp images (55.0 HU, 45.8 HU, and 47.6 HU, respectively; 65 keV vs 120 kVp, P = .15; 70 keV vs 120 kVp, P = .46), the contrast-to-noise ratio was greater for the 65- and 70-keV images than for the 120-kVp images (4.4, 4.1, and 2.1 respectively; P < .0005). CONCLUSION Dual-energy CT significantly improved the conspicuity of the ischemic bowel compared with conventional CT by increasing attenuation differences between ischemic and perfused segments on low-kiloelectron volt and iodine material density images.

Bowel Preparation for CT Colonography: Blinded Comparison of Magnesium Citrate and Sodium Phosphate for Catharsis

PURPOSE To compare colonic cleansing and fluid retention of double-dose magnesium citrate with those of single-dose sodium phosphate in patients undergoing computed tomographic (CT) colonography. MATERIALS AND METHODS This retrospective HIPAA-compliant clinical study had institutional review board approval; informed consent was waived. The study included 118 consecutive patients given single-dose sodium phosphate for bowel catharsis and 115 consecutive patients at risk for phosphate nephropathy, who were instead given double-dose magnesium citrate. The bowel preparation regimen was otherwise identical. Four-point scales were used to assess residual stool and fluid in the six colonic segments, and attenuation of residual fluid was measured. An a priori power analysis was performed, and unpaired t tests with Welch correction were used to compare the two groups on stool and fluid scores and fluid attenuation. RESULTS Both cathartic regimens offered excellent colon cleansing, with no significant difference for residual stool in any of the six segments. Stool scores of 1 or 2 (ie, no residual stool or residual stool <5 mm) were recorded in 88.6% (627 of 708) of colonic segments in the sodium phosphate group and in 88.1% (608 of 690) in the magnesium citrate group. No clinically important differences were seen in residual fluid scores in any of the six segments, with the only significant difference seen in the sigmoid colon (2.17 for sodium phosphate vs 2.44 for magnesium citrate; P< 0.01). Fluid attenuation was significantly different between magnesium citrate and sodium phosphate groups (790 HU +/- 216 vs 978 HU +/- 160; P <.001). CONCLUSION Both sodium phosphate and magnesium citrate provided excellent colon cleansing for CT colonography. Residual stool and fluid were similar in both groups, and fluid attenuation values were closer to optimal in the magnesium citrate group. Since bowel preparation provided by both cathartics was comparable, magnesium citrate should be considered for CT colonography, particularly in patients at risk for phosphate nephropathy.