Alvin C. Silva

Iterative Reconstruction Technique for Reducing Body Radiation Dose at CT: Feasibility Study

OBJECTIVE The purpose of this study was to evaluate the image noise, low-contrast resolution, image quality, and spatial resolution of adaptive statistical iterative reconstruction in low-dose body CT. MATERIALS AND METHODS Adaptive statistical iterative reconstruction was used to scan the American College of Radiology phantom at the American College of Radiology reference value and at one-half that value (12.5 mGy). Test objects in low- and high-contrast and uniformity modules were evaluated. Low-dose CT with adaptive statistical iterative reconstruction was then tested on 12 patients (seven men, five women; average age, 67.5 years) who had previously undergone routine-dose CT. Two radiologists blinded to scanning technique evaluated images of the same patients obtained with routine-dose CT and low-dose CT with and without adaptive statistical iterative reconstruction. Image noise, low-contrast resolution, image quality, and spatial resolution were graded on a scale of 1 (best) to 4 (worst). Quantitative noise measurements were made on clinical images. RESULTS In the phantom, low- and high-contrast and uniformity assessments showed no significant difference between routine-dose imaging and low-dose CT with adaptive statistical iterative reconstruction. In patients, low-dose CT with adaptive statistical iterative reconstruction was associated with CT dose index reductions of 32-65% compared with routine imaging and had the least noise both quantitatively and qualitatively (p < 0.05). Low-dose CT with adaptive statistical iterative reconstruction and routine-dose CT had identical results for low-contrast resolution and nearly identical results for overall image quality (grade 2.1-2.2). Spatial resolution was better with routine-dose CT (p = 0.004). CONCLUSION These preliminary results support body CT dose index reductions of 32-65% when adaptive statistical iterative reconstruction is used. Studies with larger statistical samples are needed to confirm these findings.

Innovations in CT Dose Reduction Strategy: Application of the Adaptive Statistical Iterative Reconstruction Algorithm

OBJECTIVE The purpose of this article is to discuss the application of a new CT reconstruction algorithm, adaptive statistical iterative reconstruction (ASIR), to reduce radiation dose at body CT and to provide imaging examples in comparison with low-dose and standard-dose filtered back projection CT. CONCLUSION The ASIR reconstruction algorithm is a promising technique for providing diagnostic quality CT images at significantly reduced radiation doses.

Abdominal CT: Comparison of Low-Dose CT With Adaptive Statistical Iterative Reconstruction and Routine-Dose CT With Filtered Back Projection in 53 Patients

OBJECTIVE The purpose of this article is to retrospectively compare radiation dose, noise, and image quality of abdominal low-dose CT reconstructed with adaptive statistical iterative reconstruction (ASIR) and routine-dose CT reconstructed with filtered back projection (FBP). MATERIALS AND METHODS Fifty-three patients (37 men and 16 women; mean age, 60.8 years) underwent contrast-enhanced abdominal low-dose CT with 40% ASIR. All 53 patients had previously undergone contrast-enhanced routine-dose CT with FBP. With the scanning techniques masked, two radiologists independently graded images for sharpness, image noise, diagnostic acceptability, and artifacts. Quantitative measures of radiation dose and image noise were also obtained. All results were compared on the basis of body mass index (BMI). RESULTS The volume CT dose index (CTDI(vol)), dose-length product, and radiation dose for low-dose CT with ASIR were 17 mGy, 860 mGy, and 13 mSv, respectively, compared with 25 mGy, 1,193 mGy, and 18 mSv for routine-dose CT with FBP, representing an approximate overall dose reduction of 33%. Low-dose CT with ASIR had significantly reduced (p < 0.001) quantitative and qualitative assessment of image noise. Image sharpness, however, was significantly reduced for low-dose CT with ASIR (p < 0.001), although diagnostic acceptability and artifact scores were nearly identical to those for routine-dose CT with FBP. The average CTDI(vol) dose reduction was 66% for patients with a BMI of less than 20 and 23% for patients with a BMI of 25 or greater. CONCLUSION Compared with routine-dose CT with FBP, abdominal low-dose CT with ASIR significantly reduces noise, thereby permitting diagnostic abdominal examinations with lower (by 23-66%) radiation doses. Despite reduced image sharpness in average and small patients, low-dose CT with ASIR had diagnostic acceptability comparable to that of routine-dose CT with FBP.

Dual-Energy (Spectral) CT: Applications in Abdominal Imaging

Dual-energy imaging is a promising new development in computed tomography (CT) that has the potential to improve lesion detection and characterization beyond levels currently achievable with conventional CT techniques. In dual-energy CT (DECT), the simultaneous use of two different energy settings allows the differentiation of materials on the basis of their energy-related attenuation characteristics (material density). The datasets obtained with DECT can be used to reconstruct virtual unenhanced images as well as iodinated contrast material-enhanced material density images, obviating the standard two-phase (unenhanced and contrast-enhanced) scanning protocol and thus helping minimize the radiation dose received by the patient. Single-source DECT, which is performed with rapid alternation between two energy levels, can also generate computed monochromatic images, which are less vulnerable to artifacts such as beam hardening and pseudoenhancement and provide a higher contrast-to-noise ratio than polychromatic images produced by conventional CT. Familiarity with the capabilities of DECT may help radiologists improve their diagnostic performance.

Reducing the Radiation Dose for CT Colonography Using Adaptive Statistical Iterative Reconstruction: A Pilot Study

OBJECTIVE The purpose of our study was to evaluate the feasibility of preserving image quality during CT colonography (CTC) using a reduced radiation dose with adaptive statistical iterative reconstruction (ASIR). MATERIALS AND METHODS A proven colon phantom was imaged at standard dose settings (50 mAs) and at reduced doses (10-40 mAs) using six different ASIR levels (0-100%). We assessed 2D and 3D image quality and noise to determine the optimal dose and ASIR setting. Eighteen patients were then scanned with a standard CTC dose (50 mAs) in the supine position and at a reduced dose of 25 mAs with 40% ASIR in the prone position. Three radiologists blinded to the scanning techniques assessed 2D and 3D image quality and noise at three different colon locations. A score difference of > or = 1 was considered clinically important. Actual noise measures were compared between the standard-dose and low-dose acquisitions. RESULTS The phantom study showed image noise reduction that correlated with a higher percentage of ASIR. In patients, no significant image quality differences were identified between standard- and low-dose images using 40% ASIR. Overall image quality was reduced for both image sets as body mass index increased. Measured image noise was less with the low-dose technique using ASIR. CONCLUSION The results of this pilot study show that the radiation dose during CTC can be reduced 50% below currently accepted low-dose techniques without significantly affecting image quality when ASIR is used. Further evaluation in a larger patient group is warranted.

Integrated genomic characterization reveals novel, therapeutically relevant drug targets in FGFR and EGFR pathways in sporadic intrahepatic cholangiocarcinoma.

Advanced cholangiocarcinoma continues to harbor a difficult prognosis and therapeutic options have been limited. During the course of a clinical trial of whole genomic sequencing seeking druggable targets, we examined six patients with advanced cholangiocarcinoma. Integrated genome-wide and whole transcriptome sequence analyses were performed on tumors from six patients with advanced, sporadic intrahepatic cholangiocarcinoma (SIC) to identify potential therapeutically actionable events. Among the somatic events captured in our analysis, we uncovered two novel therapeutically relevant genomic contexts that when acted upon, resulted in preliminary evidence of anti-tumor activity. Genome-wide structural analysis of sequence data revealed recurrent translocation events involving the FGFR2 locus in three of six assessed patients. These observations and supporting evidence triggered the use of FGFR inhibitors in these patients. In one example, preliminary anti-tumor activity of pazopanib (in vitro FGFR2 IC50≈350 nM) was noted in a patient with an FGFR2-TACC3 fusion. After progression on pazopanib, the same patient also had stable disease on ponatinib, a pan-FGFR inhibitor (in vitro, FGFR2 IC50≈8 nM). In an independent non-FGFR2 translocation patient, exome and transcriptome analysis revealed an allele specific somatic nonsense mutation (E384X) in ERRFI1, a direct negative regulator of EGFR activation. Rapid and robust disease regression was noted in this ERRFI1 inactivated tumor when treated with erlotinib, an EGFR kinase inhibitor. FGFR2 fusions and ERRFI mutations may represent novel targets in sporadic intrahepatic cholangiocarcinoma and trials should be characterized in larger cohorts of patients with these aberrations.

MR Imaging of Hypervascular Liver Masses: A Review of Current Techniques

Major technologic advances in magnetic resonance (MR) imaging, including the advent of novel pulse sequences (eg, diffusion-weighted and steady-state free precession sequences) and the use of hepatocyte-specific contrast agents, have led to better image quality and shorter acquisition times, resulting in dramatic improvements in the noninvasive detection and characterization of hepatic lesions, particularly hypervascular neoplasms. However, as the role of MR imaging in clinical evaluation of the liver continues to evolve, keeping abreast of new developments can be daunting as well as confusing. A systematic approach that makes use of a simple decision algorithm can help differentiate hypervascular hepatic lesions on the basis of their distinguishing MR imaging characteristics and related clinical information.

Preliminary Estimate of Triphasic CT Enterography Performance in Hemodynamically Stable Patients With Suspected Gastrointestinal Bleeding

OBJECTIVE The objective of our study was to retrospectively evaluate the performance of triphasic CT enterography and identify causes of false-negative CT results in hemodynamically stable patients with suspected gastrointestinal bleeding. MATERIALS AND METHODS A retrospective review of 48 patients (male-female ratio, 22:26) with suspected gastrointestinal bleeding (first-episode gastrointestinal bleed, n = 19; obscure gastrointestinal bleed, n = 29) who underwent triphasic CT enterography was performed. All patients had endoscopic, pathologic, or other imaging confirmation within 3 months of triphasic CT enterography. The sensitivity and specificity of triphasic CT enterography were calculated using pathology, endoscopy, or other imaging confirmation as the reference standard. Results were retrospectively reviewed to determine the cause of missed findings at triphasic CT enterography. RESULTS The overall sensitivity and specificity of triphasic CT enterography for detecting gastrointestinal bleeding was 33% (7/21) and 89% (24/27), respectively. Sensitivity and specificity were higher in first-episode gastrointestinal bleed cases (42% and 100%, respectively) than in obscure gastrointestinal bleed cases (22% and 85%). In the subset of patients undergoing capsule endoscopy (n = 17), only triphasic CT enterography identified two of three bleeding sources. Triphasic CT enterography did not identify six ulcers, four vascular malformations, two hemorrhoids, a duodenal mass, and a bleeding colonic diverticulum. The missed findings at triphasic CT enterography were attributed to being CT occult (n = 9), perception errors (n = 4), and technical errors (n = 1). If perception errors are excluded, the sensitivity of triphasic CT enterography increases to 52% (11/21). CONCLUSION Triphasic CT enterography can be a useful and complementary test in the evaluation of clinically stable patients with suspected gastrointestinal bleeding by identifying the bleeding source in one third to one half of patients. Because of the potential for perception errors, radiologists should familiarize themselves with the appearance of bleeding sources at CT enterography.

Applications of Dual-Energy CT in Urologic Imaging: An Update

This article discusses modern dual-energy computed tomography (DECT) and the unique material-specific information these scanners can provide. A description of the technical aspects of the various DECT techniques is provided. Specific clinical applications in urologic imaging, including chemical composition of urolithiasis, evaluation of renal masses, detection of urothelial neoplasms, and adrenal adenoma imaging, are discussed. The unique postprocessed image sets, including virtual noncontrast, iodine overlay, and stone composition, are described.

US-guided Renal Transplant Biopsy: Efficacy of a Cortical Tangential Approach

PURPOSE To describe the cortical tangential approach to ultrasonographically (US) guided renal transplant biopsy and evaluate its efficacy in obtaining sufficient cortical tissue. MATERIALS AND METHODS This HIPAA-compliant retrospective study was exempted from review by the institutional review board. Informed consent was not required. The number of core biopsy samples, glomeruli, and small arteries obtained during 294 consecutive US-guided renal transplant biopsies in 254 patients (134 men, 120 women; age range, 19-79 years; mean age, 52.2 years) in one department between June 1 and December 31, 2008, were recorded, along with any ensuing complications. Procedural success was assessed according to Banff 97 criteria. RESULTS There were 1.2 +/- 0.4 (standard deviation) biopsy core samples taken per case by 11 radiologists using the cortical tangential approach. In 290 cases, biopsy results showed 21.7 +/- 10.1 glomeruli and 5.0 +/- 2.8 small arteries. Two hundred seventy-six (95%) cases were adequate or minimal according to Banff 97 assessment criteria. Of the 14 inadequate cases (5%), six were lacking only one glomerulus to achieve minimal status. Only one biopsy core sample was taken in all 14 inadequate cases and in 233 successful cases (success rate, 85%). None of the 43 cases with two or more biopsy core samples taken were inadequate (success rate, 100%). Two patients (0.7%) had a hemorrhagic complication requiring transfusion, and another four patients (1.4%) experienced a minor self-limiting complication. CONCLUSION The cortical tangential approach can be used by a cohort of radiologists to achieve 95% or higher collective success in obtaining cortical tissue during renal transplant biopsy, with few complications. The success rate is higher, without increased complications, when more than one core specimen is taken.