Object shape dependency of in-plane resolution for iterative reconstruction of computed tomography.

The present study aimed to investigate whether the in-plane resolution property of iterative reconstruction (IR) of computed tomography (CT) data is object shape-dependent by testing columnar shapes with diameters of 3, 7, and 10cm (circular edge method) and a cubic shape with 5-cm side lengths (linear edge method). For each shape, objects were constructed of acrylic (contrast in Hounsfield units [ΔHU]=120) as well as a soft tissue equivalent material (ΔHU=50). For each shape, we measured the modulation transfer functions (MTFs) of IR and filtered back projection (FBP) using two multi-slice CT scanners at scan doses of 5 and 10mGy. In addition, we evaluated a thin metal wire using the conventional method at 10mGy. For FBP images, the MTF results of the tested objects and the wire method showed substantial agreement, thus demonstrating the validity of our analysis technique. For IR images, the MTF results of different shapes were nearly identical for each object contrast and dose combination, and we did not observe shape-dependent effects of the resolution properties of either tested IR. We conclude that both the circular edge method and linear edge method are equally useful for evaluating the resolution properties of IRs.

128-slice dual-source CT coronary angiography with prospectively electrocardiography-triggered high-pitch spiral mode: radiation dose, image quality, and diagnostic acceptability.

BACKGROUND: Dual-source computed tomography (CT) enables CT coronary angiography (CTCA) with a prospectively electrocardiography (ECG)-triggered high-pitch spiral (HPS) mode. PURPOSE: To evaluate the radiation dose, image quality, and diagnostic acceptability of the HPS mode in CTCA and to compare HPS with the step-and-shoot (SAS) and low-pitch spiral (LPS) modes. MATERIAL AND METHODS: One hundred and thirty-eight patients who underwent CTCA with a 128-slice dual-source CT scanner were retrospectively included in this study. Seventeen patients (average heart rate of ≤65 beats per minute [bpm] prior to acquisition) were evaluated in the HPS mode, 88 (average heart rate of >65 and ≤80 bpm prior to acquisition) in the SAS mode, and 33 (average heart rate of >80 bpm prior to acquisition or patients with an unstable heart rhythm) in the LPS mode. Radiation dose and image noise were recorded for each patient. Diagnostic acceptability was graded using a four-point scale (1, unacceptable; 2, suboptimal; 3, acceptable; 4, fully acceptable). RESULTS: The effective dose in the HPS mode was 1.5 ± 0.2 mSv, which was lower than that in SAS (8.9 ± 2.7 mSv) and LPS (21.5 ± 4.3 mSv) modes. There were no significant differences in the image noise levels in the descending aorta and left atrium. The average per-patient diagnostic acceptability was 3.2, 3.6, and 3.7 in HPS, SAS, and LPS modes, respectively. CONCLUSION: The radiation dose is lower with HPS than with other modes, and the HPS mode-acquired images of patients with heart rates of ≤65 bpm are nearly acceptable for diagnostic image interpretation.

[Phantom Study on Dose Reduction Using Iterative Reconstruction in Low-dose Computed Tomography for Lung Cancer Screening].

We investigated dose reduction ability of an iterative reconstruction technology for low-dose computed tomography (CT) for lung cancer screening. The Sinogram Affirmed Iterative Reconstruction (SAFIRE) provided in a multi slice CT system, Somatom Definition Flash (Siemens Healthcare) was used. An anthropomorphic chest phantom (N-1, Kyoto Kagaku) was scanned at volume CT dose index (CTDIvol) of 0.50-11.86 mGy with 120 kV. For noise (standard deviation) and contrast-to-noise ratio (CNR) measurements, CTP486 and CTP515 modules in the Catphan (The Phantom Laboratory) were scanned. Radiological technologists were participated in the perceptual comparison. SAFIRE reduced the SD values by approximately 50% compared with filter back projection (FBP). The estimated dose reduction rates by SAFIRE determined from the perceptual comparison was approximately 23%, while 75% dose reduction rate was expected from the SD value reduction of 50%.

[Evaluation of dose output according to the objects using organ-based tube-current modulation in thoracic computed tomography].

The purpose of this study was to evaluate the dose output according to the object using organ-based tube-current modulation in thoracic CT. The output doses with elliptical and circular shaped phantoms were measured using an ionizing CT chamber. The image noise was quantitatively measured in images obtained from the elliptical phantom. Although total dose outputs with and without the modulation were almost the same, dose outputs at a frontal angle of 120° decreased and those at another angle of 240° increased with the modulation. When the same-shaped phantoms were used, the differences in variation of dose outputs due to the difference in phantom size were small and those due to the difference in the percentage ratio of long- to short-axis diameter of the cross-section were large. There was no significant difference in the amount of noise with and without the dose modulation except for the case of overdose to the small phantom. Therefore, organ-based tube current modulation does not change the total dose output and it maintains the amount of noise by controlling the dose output for each projection angle. Additionally, this dose control is independent of the object size.