Application of subsecond rotation scan to helical CT for lung cancer screening.

PURPOSE: To clarify whether the benefit of a reduced effective scan width obtained using a smaller pitch outweighs the disadvantage of increased noise in the application of a subsecond helical CT to mass screenings for lung cancer. MATERIALS AND METHODS: Twenty-two helical CT scans of the lung were obtained in 11 healthy subjects using the following parameters: 1) scan 1 was performed at 120 kVp, 50 mA, 10-mm collimation, 1-second/rotation, helical pitch of 2.0; and 2) scan 2 was performed at 120 kVp, 50 mA, 10-mm collimation, 0.75-second/rotation, helical pitch of 1.5. Computer-generated nodules measuring 10 mm and 6 mm in diameter showing ground-glass opacity were superimposed on these images. The detectability of each nodule was evaluated by six blinded readers using ROC analysis. RESULTS: Detectability of the 6-mm nodules was significantly higher in scan 2 than in scan 1. Detectability of the 10-mm nodules was not significantly different between scans 1 and 2. CONCLUSION: The use of a smaller pitch by employing a subsecond rotation scan in a helical CT for lung cancer screenings improves the detection of small lesions without increasing either the scanning time or radiation dose.

Three-phase CT examination of the pancreatobiliary region using multislice CT with 1-mm collimation.

PURPOSE: To evaluate the degree of contrast enhancement and accuracy of imaging of the circulatory phase in the first-pass, second-pass, and third-pass acquisitions in the pancreato-biliary region with 1-mm collimation obtained by multislice computed tomography (CT). MATERIALS AND METHODS: In 53 patients, two sequential acquisitions from the porta hepatis to the pancreas were performed during a single breath-hold, followed by a third-pass acquisition including the liver beginning 15 sec after the second-pass acquisition. Contrast enhancement in each acquisition was measured in the aorta, portal vein and its branches, and pancreas. Four experienced radiologists graded using four-point scoring whether or not each acquisition was appropriate for imaging of the arterial phase, pancreatic phase, and portal venous phase. RESULTS: Aortic enhancement was highest at the beginning of the second-pass acquisition. The portal and splenic veins and pancreas showed maximum enhancement in the second-pass acquisition, while the superior mesenteric vein showed maximum enhancement in the third-pass acquisition. In the visual assessment, significantly higher grades were achieved in the first-pass, second-pass, and third-pass acquisitions with regard to imaging of the arterial phase, pancreatic phase, and portal venous phase, respectively. CONCLUSION: Multislice CT permits the acquisition of three distinct circulatory phases (arterial, pancreatic, and portal venous phases) in the pancreatobiliary region with 1-mm collimation.

Diagnostic value of SPIO-mediated breath-hold, black-blood, fluid-attenuated, inversion recovery (BH-BB-FLAIR) imaging in patients with hepatocellular carcinomas.

PURPOSE: We assessed the value of adding a breath-hold, black-blood, fluid-attenuated, inversion recovery (BH-BB-FLAIR) sequence with a small motion-probing gradient (b=10 s/mm(2)) using superparamagnetic iron oxide (SPIO) to our present studies that utilize SPIO to detect hepatocellular carcinoma (HCC). We used inversion recovery (IR) in a FLAIR sequence to suppress signals from cysts and a low b-value to suppress vessel signals and provide higher signal to noise than that using high b-value diffusion-weighted imaging. Use of SPIO is expected to reduce the signal in both normal liver parenchyma and in most benign lesions. MATERIALS AND METHODS: In 19 patients, we reviewed 38 HCC nodules diagnosed by CT arterioportography (CTAP) and CT during hepatic arteriography (CTHA). We divided SPIO-mediated images into sets, those obtained with and without BH-BB-FLAIR. Six radiologists individually interpreted the 2 image sets and sorted them by their confidence levels for the presence of HCC, and we calculated the area under the receiver operating characteristic (ROC) curve (Az) for each image set. RESULTS: On images obtained with BH-BB-FLAIR after SPIO administration, 33 of the 38 HCC nodules appeared as areas of high signal and cyst signal was extinguished. The ROC analysis showed significantly higher Az values in the set with BH-BB-FLAIR (0.89) than in the set without (0.83). CONCLUSIONS: Adding BH-BB-FLAIR to existing SPIO-mediated imaging protocols improved detection of HCC nodules and added only 24 s to the scan time.

Lung: feasibility of a method for changing tube current during low-dose helical CT.

A method for changing the tube current during helical scanning was applied to low-dose computed tomography (CT) in the lung. The changing method resulted in significant equalization of image noise in various lung sections compared with that at scanning with constant tube current. Detectability of nodules was equivalent between 60 mA and the changing method, whereas degradation occurred at 20 mA. This method seems feasible for the low-dose CT of lung cancer screening.