Priyanka Prakash

Reducing abdominal CT radiation dose with adaptive statistical iterative reconstruction technique.

Purpose:To assess radiation dose reduction for abdominal computed tomography (CT) examinations with adaptive statistical iterative reconstruction (ASIR) technique. Materials and Methods:With institutional review board approval, retrospective review of weight adapted abdominal CT exams were performed in 156 consecutive patients with ASIR and in 66 patients with filtered back projection (FBP) on a 64-slice MDCT. Patients were categorized into 3 groups of <60 kg (n = 42), 61 to 90 kg (n = 100), and ≥91 kg (n = 80) for weight-based adjustment of automatic exposure control technique. Remaining scan parameters were held constant at 1.375:1 pitch, 120 kVp, 55 mm table feed per rotation, 5 mm section thickness. Two radiologists reviewed all CT examinations for image noise and diagnostic acceptability. CT dose index volume, and dose length product were recorded. Image noise and transverse abdominal diameter were measured in all patients. Data were analyzed using analysis of variance. Results:ASIR allowed for an overall average decrease of 25.1% in CT dose index volume compared with the FBP technique (ASIR, 11.9 ± 3.6 mGy; FBP, 15.9 ± 4.3 mGy) (P < 0.0001). In each of the 3 weight categories, CT examinations reconstructed with ASIR technique were associated with significantly lower radiation dose compared with FBP technique (P < 0.0001). There was also significantly less objective image noise with ASIR (6.9 ± 2.2) than with FBP (9.5 ± 2.0) (P < 0.0001). For the subjective analysis, all ASIR and FBP reconstructed abdominal CTs had optimal or less noise. However, 9% of FBP and 3.8% of ASIR reconstructed CT examinations were diagnostically unacceptable because of the presence of artifacts. Use of ASIR reconstruction kernel results in a blotchy pixilated appearance in 39% of CT sans which however, was mild and did not affect the diagnostic acceptability of images. The critical reproduction of visually sharp anatomic structures was preserved in all but one ASIR 40% reconstructed CT examination. Conclusion:ASIR technique allows radiation dose reduction for abdominal CT examinations whereas improving image noise compared with the FBP technique.

Diffuse Lung Disease: CT of the Chest with Adaptive Statistical Iterative Reconstruction Technique

PURPOSE To compare visualization of subtle normal and abnormal findings at computed tomography (CT) of the chest for diffuse lung disease with images reconstructed with filtered back projection and adaptive statistical iterative reconstruction (ASIR) techniques. MATERIALS AND METHODS In this HIPAA-compliant, institutional review board-approved study, 24 patients underwent 64-section multi-detector row CT of the chest for evaluation of diffuse lung disease. Scanning parameters included a pitch of 0.984:1 and 120 kVp in thin-section mode, with 2496 views per rotation compared with 984 views acquired for normal mode. The 0.625-mm-thick images were reconstructed with filtered back projection, ASIR, and ASIR high-definition (ASIR-HD) kernels. Two thoracic radiologists independently assessed the filtered back projection, ASIR, and ASIR-HD images for small anatomic details (interlobular septa, centrilobular region, and small bronchi and bronchioles), abnormal findings (reticulation, tiny nodules, altered attenuation, bronchiectasis), image quality (graded by using a six-point scale, where 1 = excellent image quality, and 5 = interpretation impossible), image noise, and artifacts. Data were tabulated for statistical testing. RESULTS For visualization of normal and pathologic structures, CT image series reconstructed with ASIR-HD were rated substantially better than those reconstructed with filtered back projection and ASIR (P < .001). ASIR-HD images were superior to filtered back projection images in 15 of 24 (62%) patients for visualization of normal structures and in 24 of 24 (100%) patients for pathologic findings. ASIR-HD was superior to ASIR in three of 24 (12%) images for normal anatomic findings and in seven of 24 (29%) images for pathologic evaluation. None of the images in the three groups were rated as unacceptable for noise (P < .001). CONCLUSION ASIR-HD reconstruction results in superior visualization of subtle and tiny anatomic structures and lesions in diffuse lung disease compared with ASIR and filtered back projection reconstructions.

Low-Dose CT Examinations in Crohn's Disease: Impact on Image Quality, Diagnostic Performance, and Radiation Dose

OBJECTIVE The objective of this study was to evaluate the image quality and diagnostic performance of simulated low-dose MDCT examinations in patients with Crohns disease. MATERIALS AND METHODS Thirty-five MDCT examinations from 25 patients (14 males and 11 females; age range, 16-86 years) with known or suspected Crohns disease were retrospectively evaluated. The MDCT images (5 mm thickness) were modified by artificially introducing noise using volume CT noise simulation software to simulate low-dose MDCT data acquired with noise indexes (NIs) of 18-35. The 175 MDCT image data sets generated were then randomized and reviewed by two readers to assess the subjective image quality and diagnostic accuracy for confidently detecting Crohns disease findings on a 5-point scale (1, definitely absent; 5, definitely present). The image quality, diagnostic performance, and radiation dose from the original MDCT examinations served as a reference standard for comparison. RESULTS The simulated low-dose CT images with elevated NIs of 18-25 yielded optimal image quality and concordant diagnostic accuracy with standard-dose scans with a mean baseline volume CT dose index of 16 +/- 3.34 (SD) mGy (image quality score, 4-4.9 vs 4.95, respectively; p = 0.4). Images simulating NIs of 30-35 were considered degraded because of excessive image noise and presented lower diagnostic performance (range of image quality score, 3-3.6; weighted kappa = 0.25-0.37; p < 0.001). Diagnostic performance and reader confidence for the determination of Crohns disease manifestations in cases in which the reference standard was positive were higher at NIs of < or = 25 compared with NI of 30 (reader confidence score, 4.5 vs 3.6, respectively; p < 0.05) and an NI of 35 (3.2, p < 0.05). Compared with the standard-dose examination, a 31-64% reduction in radiation dose was estimated for NI levels of 18-25, which corresponds to image noise of 19-27 HU in subcutaneous fat. CONCLUSION Processed MDCT images with the introduction of noise to simulate low-dose MDCT examinations with NI levels of 18-25 allows substantial dose reduction for CT examinations in Crohns disease without compromising diagnostic information.

Role of PET/CT in Ovarian Cancer

OBJECTIVE The purpose of this article is to review the role of FDG PET/CT in ovarian cancer, which is the leading cause of death among gynecologic cancers. CONCLUSION FDG PET/CT can significantly modify the assessment of the extent of primary and recurrent ovarian cancer and, hence, often alters patient management substantially. FDG PET/CT has thus become a critical tool for the preoperative evaluation of women with primary ovarian cancer and for postoperative follow-up assessment for evidence of recurrence in these patients.

Evolution of Coronary Computed Tomography Radiation Dose Reduction at a Tertiary Referral Center

PURPOSE We aimed to assess the temporal change in radiation doses from coronary computed tomography angiography (CCTA) during a 6-year period. High CCTA radiation doses have been reduced by multiple technologies that, if used appropriately, can decrease exposures significantly. METHODS A total of 1277 examinations performed from 2005 to 2010 were included. Univariate and multivariable regression analysis of patient- and scan-related variables was performed with estimated radiation dose as the main outcome measure. RESULTS Median doses decreased by 74.8% (P<.001), from 13.1 millisieverts (mSv) (interquartile range 9.3-14.7) in period 1 to 3.3 mSv (1.8-6.7) in period 4. Factors associated with greatest dose reductions (P<.001) were all most frequently applied in period 4: axial-sequential acquisition (univariate: -8.0 mSv [-9.7 to -7.9]), high-pitch helical acquisition (univariate: -8.8 mSv [-9.3 to -7.9]), reduced tube voltage (100 vs 120 kV) (univariate: -6.4 mSv [-7.4 to -5.4]), and use of automatic exposure control (univariate: -5.3 mSv [-6.2 to -4.4]). CONCLUSIONS CCTA radiation doses were reduced 74.8% through increasing use of dose-saving measures and evolving scanner technology.

Brown Fat at PET/CT: Correlation with Patient Characteristics

PURPOSES To assess the prevalence of brown fat in patients with cancer, compare demographic characteristics of those with and those without brown fat, and correlate these characteristics with the mean and maximum standardized uptake values of brown fat. MATERIALS AND METHODS This case-control study was institutional review board approved and HIPAA compliant. Informed consent was waived. Reports of 12 195 consecutive positron emission tomography/computed tomography examinations performed in 6867 patients between January 2004 and November 2008 were reviewed for documented fluorodeoxyglucose (FDG) uptake in brown fat (n = 298). Control patients (n = 298) without brown fat were chosen and matched for age, sex, and month and year of examination. Age, sex, weight, body mass index, ethnicity, and examination stage (initial vs restaging) were compared between groups. Paired Student t test, χ(2) test, Pearson correlation coefficient, and analysis of variance were used for statistical analysis. RESULTS Uptake of FDG in brown fat was demonstrated in 298 of 6867 (4.33%) patients. Prevalence of brown fat was significantly higher in female (5.9% [211 of 3587]) than in male patients (2.65% [87 of 3280]; P < .001). Those with brown fat had significantly lower body weight (147.5 lb ± 3.8 vs 168.61 lb ± 5.0; P < .001) and body mass index (24.3 ± 0.54 vs 27.6 ± 0.77; P < .001) than control patients. There was no significant difference in the prevalence of brown fat among ethnic groups. The maximum standardized uptake value of brown fat had a significant inverse correlation with age (r = -0.3, P < .001). CONCLUSION Patients with brown fat were more likely to be female and thinner than those without brown fat. Younger patients were more likely to have higher maximum standardized uptake values of brown fat.

PET/CT for Adrenal Assessment

W91 Imaging Features Normal Adrenal Gland The normal adrenal gland is larger than the spatial resolution of PET; however, it is usually barely visible on FDG PET. Combined PET/ CT can show normal mild FDG uptake in the location of the glands visible on the coregistered CT (Figs. 1 and 2). The average mean and maximum standardized uptake values (SUVs) are 0.90 ± 0.15 (SD) and 0.83 ± 0.17, respectively, for the right adrenal and 1.10 ± 0.15 and 0.946 ± 0.15 for the left adrenal. The maximum SUVs of normal adrenal glands range from 0.95 to 2.46 [4]. An adrenal is usually considered malignant if its intensity is higher than that of the liver; however, because the average mean SUV of the liver is 1.5–2.0, physiologic adrenal uptake may, in some cases, be in the range of malignant lesions.

FDG PET/CT in Assessment of Pulmonary Lymphangitic Carcinomatosis

OBJECTIVE The purpose of this study was to assess the role of PET/CT in the diagnosis of pulmonary lymphangitic carcinomatosis. MATERIALS AND METHODS Integrated PET/CT images of 35 patients (15 men, 20 women; mean age, 64.5 years) with pulmonary lymphangitic carcinomatosis confirmed at follow-up chest CT or histopathologic examination were analyzed retrospectively. Standardized uptake value based on body weight and the initial injected activity was measured in the affected lung, the normal lung, and the mediastinal blood pool. Two radiologists independently assessed abnormal PET activity in the lungs. Both radiologists reviewed the CT images to determine the presence, size, location, and extent of pulmonary lymphangitic carcinomatosis. The data were analyzed to determine the sensitivity and specificity of PET for pulmonary lymphangitic carcinomatosis. RESULTS Among the 35 patients with pulmonary lymphangitic carcinomatosis, 17 (49%), 13 (37%), and five (14%) patients had diffuse, focal, and bilateral pulmonary lymphangitic carcinomatosis, respectively. Thirty of the 35 patients had nodular septal thickening as the chief CT finding of pulmonary lymphangitic carcinomatosis. Subjective assessment showed a visually identifiable increase in uptake in the region of pulmonary lymphangitic carcinomatosis in 30 of the 35 patients (86%). Four of the other five patients had focal pulmonary lymphangitic carcinomatosis, and one patient had diffuse pulmonary lymphangitic carcinomatosis of the right lung. The specificity of PET/CT for pulmonary lymphangitic carcinomatosis was 100%, and the sensitivity was 86%. The mean standardized uptake value in the region of pulmonary lymphangitic carcinomatosis (1.37+/-0.64) was significantly greater than that in normal lung (0.51+/-0.29) (p<0.0001). The standardized uptake ratio of mediastinal blood pool to lymphangitic lung was 1.26+/-0.45, and that of blood pool to normal lung was 3.78+/-1.37. CONCLUSION FDG PET/CT has high specificity in the detection of pulmonary lymphangitic carcinomatosis. Focal pulmonary lymphangitic carcinomatosis close to a primary malignant tumor, however, can be missed at PET.

Oral and IV contrast agents for the CT portion of PET/CT.

W5 the lesion and adjacent structures and CT enhancement characteristics such as phase and pattern. Most parenchymal organs and the lesions affecting them have similar attenuation values, which lie within a relatively narrow range, typically 30–80 HU. IV contrast material is used to increase the attenuation difference between normal and abnormal tissue. The result is increased lesion conspicuity, which is of particular importance in lesions in which FDG does not accumulate (Figs. 1–3). Furthermore, IV contrast enhancement can help differentiate benign from malignant lesions that have nonspecific FDG PET uptake. Similarly, IV contrast material may outline lesions within vascular structures (Figs. 1 and 4) and localize lesions that have increased FDG uptake but that would not be clearly seen on unenhanced CT images because of absence of a contour abnormality due to their size or would have similar attenuation to the surrounding structures (Fig. 5). The pyeloureteral system may not be well visualized at PET/CT because urinary excretion of FDG masks lesions. In addition, some renal lesions do not exhibit substantial FDG uptake (Fig. 6). Asymmetric FDG uptake should raise suspicion of transitional cell cancer, renal cancer, lymphoma, and ureteric obstruction or diverticulum. Asymmetric lack of uptake raises suspicion of renal cell cancer and renal cysts (Fig. 7).

Imaging-guided suprapubic bladder tube insertion: experience in the care of 549 patients.

OBJECTIVE Symptomatic bladder outlet obstruction and neurogenic bladder are common conditions that frequently necessitate suprapubic insertion of a bladder tube. The purpose of this study was to describe an experience with minimally invasive imaging-guided percutaneous suprapubic bladder tube placement and the clinical and technical success and complications encountered. MATERIALS AND METHODS A total of 585 primary suprapubic bladder tube insertions and 439 exchanges of suprapubic bladder tubes were performed on 549 patients (469 men, 80 women; mean age, 66 years; range, 15-106 years). The details of percutaneous tube placement (indication, tube type, size at insertion and change, and method of insertion) were retrospectively recorded. RESULTS The technical success rate for primary suprapubic bladder tube insertion was 99.6% (547/549) and for exchanges was 92.3% (405/439). The clinical success rate for primary insertion was 98.1% (572/583), and symptoms were unresolved in 1.9% (11/583). Minor complications occurred in 7.2% (42/583) of cases at tube insertion and in 4.8% (21/439) at exchange. There was one major complication (a patient needed surgery because the small bowel was traversed by a catheter), and there was no procedure-related mortality. CONCLUSION Radiologic imaging-guided percutaneous suprapubic bladder tube placement is a safe and effective procedure.