Lakshmi Ananthakrishnan

Wegener's Granulomatosis in the Chest: High-Resolution CT Findings

OBJECTIVE Wegeners granulomatosis is an uncommon necrotizing vasculitis having variable presentations in the chest that are best depicted on high-resolution CT. Imaging findings may include nodules, which may cavitate; ground-glass opacity secondary to pulmonary hemorrhage; and airway stenoses and ulcerations. Active Wegeners granulomatosis can mimic pneumonia, septic emboli, and metastases. CONCLUSION This article will illustrate the high-resolution CT findings of Wegeners granulomatosis in the chest.

Update of Dual-Energy CT Applications in the Genitourinary Tract

OBJECTIVE Dual-energy CT (DECT) is being increasingly used for abdominal imaging because it provides incremental benefit of material characterization without significant increase in radiation dose. This article provides an overview of current DECT techniques and use of DECT in urinary tract imaging for assessment of renal masses and urinary calculi characterization and in CT urography. CONCLUSION Incorporation of DECT into clinical practice and use of its material characterization capabilities in urinary tract imaging enable characterization of urinary calculi and incidental renal lesions and can reduce radiation dose by allowing generation of virtual unenhanced images.

The spectrum of renal cell carcinoma in adults

The spectrum of renal cell carcinoma (RCC) includes many neoplasms with distinct cytogenetics, biologic behaviors, and imaging appearances. The advent of molecular therapies targeting different tumor types, new insights into the relative roles of biopsy and surveillance for small incidental tumors, and a growing array of nephron-sparing interventions have altered management of RCC. Similarly, the role of the radiologist is changing, and it is becoming increasingly important for radiologists to familiarize themselves with the various types of RCC. This article introduces the reader to the common and uncommon recognized types of renal cell carcinoma and discusses how these neoplasms differ in imaging appearance and behavior.

Pseudoenhancement effects on iodine quantification from dual-energy spectral CT systems: A multi-vendor phantom study regarding renal lesion characterization

PURPOSE To measure the effect of pseudoenhancement on spectral CT iodine quantification as a function of lesion size, lesion iodine level, background iodine level, helical versus axial scanning, and spectral CT scanner type in a phantom model. MATERIALS AND METHODS A custom-built water-filled cylindrical phantom contained either six small vials (8 mm diameter) or six large vials (27 mm diameter) of aqueous iopamidol solutions (0, 0.5, 1.0, 2.0, 4.0 and 6.0 mg iodine/mL). The background iodine concentration was 0, 5, or 10 mg iodine/mL. Helical and axial scans were taken on three different dual-energy spectral CT scanners (two image-based and one projection-based) with the scan parameters consistent between the systems. ROIs were used to measure the average iodine concentration of the vials in the 36 individual scans. Linear fits of the true versus measured iodine values were used for pvalue statistical analysis. Having a y-intercept or slope p-value less than 0.05 implied statistically significant iodine quantification errors. RESULTS Iodine quantification pseudoenhancement effects are inversely proportional to lesion size and lesion enhancement and are directly proportional to background attenuation level. No significant differences between helical and axial scans were observed. 100% and 88% of the slope and y-intercept p-values were below 0.05 for the two image-based systems, while 13% of the slope and y-intercept p-values were below 0.05 for the projection-based system. CONCLUSIONS Pseudoenhancement can artificially increase spectral CT iodine quantification levels most notably for small low-enhancing lesions (<5.0 mg iodine/mL) surrounded by a high attenuating background (10 mg iodine/mL). In this study we found iodine quantification to be more accurate on projection-based spectral CT systems than image-based systems.

Imaging for Screening and Surveillance of Patients with Hereditary Forms of Renal Cell Carcinoma

Purpose of ReviewTo summarize the literature providing the basic genetic and clinical characteristics of renal cell carcinoma (RCC) familial syndromes, as well as to describe associated unique imaging characteristics and appropriate imaging protocols.Recent FindingsAt least 5–8% of RCC cases are associated with hereditary syndromes. These patients are prone to developing multiple renal tumors or associated malignancies and require more intense diagnostic and follow-up imaging studies. New familial types of RCC are continuously discovered, vis-à-vis recent characterization of BAP1 associated RCC and MITF associated cancer syndrome.SummaryWith increasing number of recognizable familial syndromes associated with RCC, physicians should be familiar with the different syndromes, the associated risks of malignancy and appropriate imaging protocols.

Separating High-Z Oral Contrast From Intravascular Iodine Contrast in an Animal Model Using Dual-Layer Spectral CT

RATIONALE AND OBJECTIVES To show that water and iodine two-material decomposition images from dual-layer dual-energy spectral X-ray computed tomography (DECT) can be used to separate intravascular iodine contrast from simultaneously administered oral tantalum, tungsten, or rhenium contrast in an animal model. MATERIALS AND METHODS In this Institutional Animal Care and Use Committee approved study, four female Fischer rats were given simultaneous intravenous and oral X-ray computed tomography contrast. Intravenous iodine contrast was administered via tail vein injection. Oral barium, tantalum, tungsten, or rhenium contrast was administered via gavage. The animals were imaged on a dual-layer DECT system at 120 kVp. Water and iodine two-material decomposition images (water equivalent and iodine equivalent images) were used for qualitative analysis. Computer simulations were performed using a customized DECT simulator to better understand why certain high-Z elements disappear in the iodine equivalent images and what is the theoretical range of elements with this property. RESULTS The iodine and barium contrast appeared only in the iodine equivalent images and could not be differentiated from each other. However, the tantalum, tungsten, and rhenium contrast only appeared in the water equivalent images. This allowed iodine contrast in the bowel wall to be easily segmented from tantalum, tungsten, and rhenium contrast in the bowel lumen. Simulations confirmed that certain high-Z elements will have pixel values of ≤0mg iodine/mL in the iodine equivalent images due to a K-edge effect associated with DECT systems. CONCLUSIONS Dual-layer DECT can separate iodine from certain high-Z elements using water equivalent and iodine equivalent images with an increased element range compared to other DECT systems. This K-edge effect could promote the development and approval of new high-Z contrast agents for DECT.

Dual-layer spectral detector CT: non-inferiority assessment compared to dual-source dual-energy CT in discriminating uric acid from non-uric acid renal stones ex vivo

PurposeTo assess the non-inferiority of dual-layer spectral detector CT (SDCT) compared to dual-source dual-energy CT (dsDECT) in discriminating uric acid (UA) from non-UA stones.MethodsFifty-seven extracted urinary calculi were placed in a cylindrical phantom in a water bath and scanned on a SDCT scanner (IQon, Philips Healthcare) and second- and third-generation dsDECT scanners (Somatom Flash and Force, Siemens Healthcare) under matched scan parameters. For SDCT data, conventional images and virtual monoenergetic reconstructions were created. A customized 3D growing region segmentation tool was used to segment each stone on a pixel-by-pixel basis for statistical analysis. Median virtual monoenergetic ratios (VMRs) of 40/200, 62/92, and 62/100 for each stone were recorded. For dsDECT data, dual-energy ratio (DER) for each stone was recorded from vendor-specific postprocessing software (Syngo Via) using the Kidney Stones Application. The clinical reference standard of X-ray diffraction analysis was used to assess non-inferiority. Area under the receiver-operating characteristic curve (AUC) was used to assess diagnostic performance of detecting UA stones.ResultsSix pure UA, 47 pure calcium-based, 1 pure cystine, and 3 mixed struvite stones were scanned. All pure UA stones were correctly separated from non-UA stones using SDCT and dsDECT (AUC = 1). For UA stones, median VMR was 0.95–0.99 and DER 1.00–1.02. For non-UA stones, median VMR was 1.4–4.1 and DER 1.39–1.69.ConclusionSDCT spectral reconstructions demonstrate similar performance to those of dsDECT in discriminating UA from non-UA stones in a phantom model.

Colonic duplication mimicking fistulizing Crohn's colitis.

To the Editor: Duplication cysts of the alimentary tract are rare, and may occur anywhere in the gastrointestinal tract, from the mouth to the anus. The colon is the least common site of congenital intestinal duplication, with 80% presenting in infancy, before the age of 2 years. 80% of duplications are cystic and the remainder are tubular. The duplicate lumens may or may not be in continuity and share a common wall, lined by colonic mucosa. Blind ending duplication anomalies typically present with chronic abdominal pain and symptoms of bowel obstruction. Here we describe an interesting case of colonic duplication in a young girl, initially thought to be a case of fistulizing Crohn’s disease (CD).