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Because MDCT use narrow cone beam x-ray, to quantitatively evaluate cone beam artifact and helical artifact is very important with different x-ray beam width (detector configuration) . The both effect (helical artifact and cone beam artifact) was confirmed on the MDCT helical scan. It does not have cone beam artifact in the Isocenter or using center detector row for conventional scan, but helical artifact basically does not depend position of x-y plane. From quantitative evaluation of cone beam artifact, helical scan has fewer cone beam artifact than conventional scan on the 200 mm position of x-y plane: the cone beam artifact index is 11.76 (8 x 2.5mm conventional scan with most edge detector row) , 6.86 (8 x 2.5mm helical pitch 0.625) and 4.9 (8 x 2.5mm helical pitch 1.675). From phantom experiment, it was concluded that cone beam angle more contribute cone beam artifact than increasing slice numbers. And it was concluded that helical scan has fewer cone beam artifact than conventional scan, because helical scan use multi detector row information and special recon algorithm with cone beam correction on the GE LightSpeed MDCT scanner.

To evaluate cardiac images obtained by multi-slice CT, assessments of the temporal resolution and reconstruction algorithm are essential. For these purposes, we have designed and developed a cardiac motion phantom. Using suitable driver sequences, the phantom allowed for modeling of real left ventricular motion, which was characterized by fast pumping, slow pumping, fast filling and slow filling. Our phantom seems to be useful for use in the fundamental assessments and researches of cardiac CT.

Multisector reconstruction is a newly devised algorithm that realizes cardiac images of high temporal resolution (0.13 msec minimum) at arbitrary phases of the cardiac cycle without degrading the signal-to-noise ratio. In this study, we examined the image quality of volunteers' examinations. Multisector reconstruction was found to be a feasible tool, providing excellent cardiac images almost without motion artifact. In addition to detecting coronary calcium, with the advantage of multidetector-row CT for good z-axis resolution and for volumetric data acquisition of the entire heart within a single breath hold, this technique could provide 3D images beneficial to the analysis of cardiac motion.

Stair-step artifact is a serious problem in reconstructed images of multiplanar reformation (MPR), surface rendering and maximum-intensity projection (MIP). We developed a new algorithm, SmartHelical Algorithm (SHA), to reduce helical artifacts. SmartHelical Algorithm reduced helical artifacts significantly with slight worsening of longitudinal resolution. Noise was reduced and SNR was increased. SHA reduced stair-step artifact in reconstructed images of MPR, surface rendering and MIP, and improved image quality.

Purpose: To reduce cardiac motion artifacts with combined use of subsecond CT scanning and a high temporal resolution algorithm., Subjects and Methods: Scan data were obtained with step-by-step scanning (scan time, 0.8 seconds). Two sets of images were reconstructed, with and without high temporal resolution reconstruction algorithm (HTRR), from the same set of scan data. HTRR, derived from modification of 180-degree linear helical interpolation, reduces full width at half maximum (FWHM) to half of the scan time. Motion artifacts of two sets of images were compared., Results: The use of HTRR seemed to be useful in reducing cardiac motion artifacts owing to the improvement of effective time resolution. However, there were some images without significant reduction of cardiac motion artifacts., Conclusion: Our technique is useful in reducing cardiac motion artifacts without an increase in radiation exposure.

We describe our trial to reduce cardiac motion artifacts on HR-CT images caused by cardiac pulsation by combining use of subsecond CT (scan time 0.8 s) and a special cine reconstruction algorithm (cine reconstruction algorithm with 180-degree helical interpolation). Eleven to 51 HR-CT images were reconstructed with the special cine reconstruction algorithm at the pitch of 0.1 (0.08 s) from the data obtained by two to six contagious rotation scans at the same level. Images with the fewest cardiac motion artifacts were selected for evaluation. These images were compared with those reconstructed with a conventional cine reconstruction algorithm and step-by-step scan. In spite of its increased radiation exposure, technical complexity and slight degradation of spatial resolution, our method was useful in reducing cardiac motion artifacts on HR-CT images in regions adjacent to the heart.

The authors proposed a new application of helical CT, namely, CT-ventriculography that can obtain 2D and 3D images of different cardiac phases. CT-ventriculography could assess wall motion, systolic thickening and chamber volume. From a single breath hold helical CT 50-rotation), about 500 transaxial slices were obtained by applying overlapping reconstruction (0.1 pitch, 0.08 sec = 0.2 mm interval). All transaxial slices were recordered to separate different cardiac phases. Then, long and short axial 2D tomograms and 3D images in different cardiac phases were reformatted. CT-ventriculography is a promising new application for the assessment of heart function.

We proposed a new helical CT approach with ECG-gated reconstruction for obtaining high quality 2D, 3D, and 4D images. Original helical images were acquired with a single helical scan with overlapping reconstruction and ECG information. Post-processing to improve temporal resolution and 4D volume set reconstruction were performed, and 2D, 3D and 4D displays were obtained. Using this new method, 2D and 3D images without cardiac motion artifacts were obtained by selecting images in diastolic phase. 2D images with cardiac motion were obtained using images of the same position and different cardiac phases. Finally, 4D images (3D images with phase information) were obtained.

We assessed the improvement of longitudinal resolution in helical CT by deblurring techniques in a phantom and 8 head and neck patients. After helical scanning with 3- or 5-mm-collimation and 3- or 5 mm/sec table feed, overlapped axial images were reconstructed at every 0.3 or 0.5 mm pitch. Deblurring techniques were applied to these data. The slice profile and longitudinal resolution were improved by deblurring. Longitudinal resolution increased with the strength of deblurring. Image sharpness was improved in reconstructed images of MPR, MIP and 3D, and better visualization of the peripheral vessels was obtained in CTAs.

As a new application of helical CT scanning we evaluated the parameters for lung cancer screening with an extremely low doses and large helical pitch. On the phantom studies, the image quality obtained with the low dose parameter was not inferior to that of the usual screening technique but artifacts were increased with the large helical pitch. A scanning technique using 120 kv, 40-60mA, 10mmth, 20mm/ sec, and a reconstruction pitch of 2 was used for lung cancer screening (screening parameters) (50 cases), and comparison was made between the detectability of the screening parameters and the routine parameters (120 kv, 200mA, 10mmth, 10-13mm/sec, and a reconstruction pitch of 1-1.3). Detectability with the screening parameters was as follows: nodular lesions (< 5mm in size: 76%. 5-10mm: 90-93% 10mm < 100%), linear lesions: 94-95%, infiltrations: 93-100%. There were no false negative lesions, when the reconstruction pitch of the screening parameters was changed from 1 to 0.25. In conclusion, reconstruction pitch had the most influence on lesion detectability.

Angiographic images of 10 adult patients with head and neck tumors were obtained by helical computed tomography (CT) using maximum intensity projection (MIP). In all cases, the vasculature of the head and neck region was clearly visualized, and hypervascular lesions were directly demonstrated. In the head and neck, bone masking is a more important problem than in other regions. We developed an effective automatic bone masking method (ABM) using 2D/3D connectivity. Helical CT angiography with MIP and ABM provided accurate anatomic depiction, and was considered to be helpful in preoperative evaluation of head and neck tumors.

The diagnostic efficacy of CT arterial portography (CTAP) for the hepatic tumors has been established. We developed the double-phase incremental CTAP (DP-CTAP) using a fast CT scanner, by which the double-phase scanning of the whole liver was made during a single contrast administration. The DP-CTAP was performed in 9 cases of hepatic diseases, and was useful for the lesion detection and improvement of the visualization of the liver vasculatures. The maximum density projection angiogram of the portal and hepatic veins was easily made by DP-CTAP images, and useful for three dimensional understanding of the liver vasculatures and the detection of the vascular abnormalities.