Dual-energy CT: a phantom comparison of different platforms for abdominal imaging

Objectives

Evaluation of imaging performance across dual-energy CT (DECT) platforms, including dual-layer CT (DLCT), rapid-kVp-switching CT (KVSCT) and dual-source CT (DSCT).

Methods

A semi-anthropomorphic abdomen phantom was imaged on these DECT systems. Scans were repeated three times for CTDIvol levels of 10 mGy, 20 mGy, 30 mGy and different fat-simulating extension rings. Over the available range of virtual-monoenergetic images (VMI), noise as well as quantitative accuracy of hounsfield units (HU) and iodine concentrations were evaluated.

Results

For all VMI levels, HU values could be determined with high accuracy compared to theoretical values. For KVSCT and DSCT, a noise increase was observed towards lower VMI levels. A patient-size dependent increase in the uncertainty of quantitative iodine concentrations is observed for all platforms. For a medium patient size the iodine concentration root-mean-square deviation at 20 mGy is 0.17 mg/ml (DLCT), 0.30 mg/ml (KVSCT) and 0.77mg/ml (DSCT).

Conclusion

Noticeable performance differences are observed between investigated DECT systems. Iodine concentrations and VMI HUs are accurately determined across all DECT systems. KVSCT and DLCT deliver slightly more accurate iodine concentration values than DSCT for investigated scenarios. In DLCT, low-noise and high-image contrast at low VMI levels may help to increase diagnostic information in abdominal CT.

Key Points

? Current dual-energy CT platforms provide accurate, reliable quantitative information. ? Dual-energy CT cross-platform evaluation revealed noticeable performance differences between different systems. ? Dual-layer CT offers constant noise levels over the complete energy range.

     

Autoimmune pancreatitis in the context of IgG4-related disease: Review of imaging findings

Current understanding of autoimmune pancreatitis (AIP) recognizes a histopathological subtype of the disease to fall within the spectrum of IgG4-related disease. Along with clinical, laboratory, and histopathological data, imaging plays an important role in the diagnosis and management of AIP, and more broadly, within the spectrum of IgG4-related disease. In addition to the defined role of imaging in consensus diagnostic protocols, an array of imaging modalities can provide complementary data to address specific clinical concerns. These include contrast-enhanced computed tomography (CT) and magnetic resonance (MR) imaging for pancreatic parenchymal lesion localization and characterization, endoscopic retrograde and magnetic resonance cholangiopancreatography (ERCP and MRCP) to assess for duct involvement, and more recently, positron emission tomography (PET) imaging to assess for extra-pancreatic sites of involvement. While the imaging appearance of AIP varies widely, certain imaging features are more likely to represent AIP than alternate diagnoses, such as pancreatic cancer. While nonspecific, imaging findings which favor a diagnosis of AIP rather than pancreatic cancer include: delayed enhancement of affected pancreas, mild dilatation of the main pancreatic duct over a long segment, the “capsule” and “penetrating duct” signs, and responsiveness to corticosteroid therapy. Systemic, extra-pancreatic sites of involvement are also often seen in AIP and IgG4-related disease, and typically respond to corticosteroid therapy. Imaging by CT, MR, and PET also play a role in the diagnosis and monitoring after treatment of involved sites.     

Using the K-edge to improve contrast conspicuity and to lower radiation dose with a 16-MDCT: a phantom and human study

PURPOSE: To study the effect of tube current (milliamperes; mA) and potential (peak kilovolt; kVp) on the attenuation values and contrast-to-noise ratios of iodine- and gadolinium-based contrast media (CM) for computed tomography angiography (CTA). MATERIALS AND METHODS: Phantom Study: A water-filled phantom with five 20-mL syringes filled with 1:20 dilution of 282, 300, 370, and 400 milligrams of iodine per milliliter concentration CM and gadopentetate dimeglumine (Magnevist, Berlex Laboratories, Wayne, NJ, 0.5 mol/L) was scanned with a 16-multidetector CT using 80, 100, 120, and 140 kVp and 500-millisecond gantry rotation time. The milliampere was either fixed at 100, 200, 300, and 380 or automatically adjusted with noise indices of 15, 20, and 25 or manually adjusted to maintain a constant image noise. The attenuation value (Hounsfield unit; HU) and its standard deviation of CM in each syringe and of the water phantom were obtained. Statistical analysis was performed to determine difference between attenuation values and contrast medium-to-water contrast-to-noise ratios at various kVp and mA selection. Human Study: Three groups of patients had CTA for abdominal aortic aneurysm with similar computed tomography parameters, varying only in kVp selection of either 100 (group A), 120 (group B), or 140 (group C). Another group (group D) had CTA at 100 kVp but with the CM volume reduced to 60%. The CTA studies were evaluated for the quality of axial and 3D images; attenuation values in the aorta, superior mesenteric artery, and iliac arteries; image noise; and scanner-estimated radiation dose. Statistical analysis was performed to determine the difference in image quality and radiation dose among the groups. RESULTS: Phantom Study: In comparison with 140 kVp, regardless of selected milliampere or noise indices, images acquired at 80, 100, and 120 kVp showed 90.8% to 94.2%, 47% to 49.7%, and 18.9% to 20.7% (P<0.0001) increase in HU of iodine-based CM, respectively, and 62.9%, 39.6%, and 16.8% (P<0.0001) increase in HU of gadolinium-based CM, respectively. Human Study: The axial images in all the groups were diagnostically acceptable. There was significantly inferior quality of axial images associated with greater image noise in group A and group D (P<0.01) in comparison with group C, but there was no difference in the quality of 3D images among the 4 groups. In comparison with group C, there was significantly higher attenuation of the aorta, superior mesenteric artery, and iliac arteries in group A (P<0.01), group B (P<0.05), and group D (P<0.01). The radiation dose (CT dose index volume) decreased to 12+/-4 in groups A and D compared with 17+/-4 in group B and 24+/-5 in group C. CONCLUSIONS: Lower kVp increases the attenuation of iodinated and gadolinium CM. CTA of the abdominal aorta performed at low kVp results in higher attenuation in aorta with reduced radiation dose and without degrading the diagnostic image quality. The iodinated CM volume can be reduced by reducing kVp during CTA.     

Predictive value of multi-detector computed tomography for accurate diagnosis of serous cystadenoma： Radiologicpathologic correlation

AIM： To identify multi-detector computed tomography （MDCT） features most predictive of serous cystadenomas （SCAs）, correlating with histopathology, and to study the impact of cyst size and MDCT technique on reader performance. METHODS： The MDCT scans of 164 patients with surgically verified pancreatic cystic lesions were reviewed by two readers to study the predictive value of various morphological features for establishing a diagnosis of SCAs. Accuracy in lesion characterization and reader confidence were correlated with lesion size （≤3 cm or 〉≥3 cm） and scanning protocols （dedicated vs routine）. RESULTS： 28/164 cysts （mean size, 39 mm; range, 8-92 mm） were diagnosed as SCA on pathology. The MDCT features predictive of diagnosis of SCA were microcystic appearance （22/28, 78.6%）, surface Iobulations （25/28, 89.3%） and central scar （9/28, 32.4%）. Stepwise logistic regression analysis showed that only microcystic appearance was significant for CT diagnosis of SCA （P = 0.0001）. The sensitivity, specificity and PPV of central scar and of combined microcystic appearance and Iobulations were 32.4%/100%/100% and 68%/100%/100%, respectively. The reader confidence was higher for lesions 〉 3 cm （P = 0.02） and for MDCT scans performed using thin collimation （1.25-2.5 mm） compared to routine 5 mm collimation exams （P 〉 0.05）. CONCLUSION： Central scar on MDCT is diagnostic of SCA but is seen in only one third of SCAs. Microcystic morphology is the most significant CT feature in diagnosis of SCA. A combination of microcystic appearance and surface Iobulations offers accuracy comparable to central scar with higher sensitivity.     

Autoimmune pancreatitis: imaging features

PURPOSE: To retrospectively determine imaging findings in patients with autoimmune pancreatitis. MATERIALS AND METHODS: Twenty-nine patients (25 male and four female; mean age, 56 years; range, 15-82 years) with histopathologic diagnosis of autoimmune pancreatitis were examined. Data were reviewed by two radiologists in consensus. Imaging findings for review included those from helical computed tomography (CT), 25 patients; magnetic resonance (MR) imaging with MR cholangiopancreatography (MRCP), four patients; endoscopic ultrasonography (US), 21 patients; endoscopic retrograde cholangiopancreatography (ERCP), 19 patients; and percutaneous transhepatic cholangiography, one patient. Images were analyzed for appearances of pancreas, biliary and pancreatic ducts, and other findings, such as peripancreatic inflammation, encasement of vessels, mass effect, pancreatic calcification, peripancreatic nodes, and peripancreatic fluid collection. Follow-up images were available in nine patients. Serologic markers such as serum immunoglobulin G (IgG) and antinuclear antibody levels were available in 12 patients. RESULTS: CT showed diffuse (n = 14) and focal (n = 7) enlargement of pancreas. Seven patients had minimal peripancreatic stranding, with lack of vascular encasement, calcification, or peripancreatic fluid collection. Nine patients had enlarged peripancreatic lymph nodes. MR imaging showed focal (n = 2) and diffuse (n = 2) enlargement with rimlike enhancement in one. MRCP revealed pancreatic duct strictures in two and sclerosing cholangitis-like appearance in one. Endoscopic US showed diffuse enlargement of pancreas with altered echotexture in 13 patients and focal mass in the head in six. ERCP showed stricture of distal common bile duct in 12 patients, irregular narrowing of intrahepatic ducts in six, diffuse irregular narrowing of pancreatic duct in nine, and focal stricture of proximal pancreatic duct in six. Serologic markers showed increased IgG and antinuclear antibody levels in seven of 12 patients. At follow-up, CT abnormalities and common bile duct strictures resolved after steroid therapy in three patients. CONCLUSION: Features that suggest autoimmune pancreatitis include focal or diffuse pancreatic enlargement, with minimal peripancreatic inflammation and absence of vascular encasement or calcification at CT and endoscopic US, and diffuse irregular narrowing of main pancreatic duct, with associated multiple biliary strictures at ERCP.     

Role of dual energy CT to improve diagnosis of non-traumatic abdominal vascular emergencies

Abdominal Radiology - Computed tomography angiography (CTA) is the modality of choice to evaluate abdominal vascular emergencies (AVE). CTA protocols are often complex and require acquisition of...