Comparison of physical image qualities and artifact indices for head computed tomography in the axial and helical scan modes.

This study aimed to validate the clinically demonstrated equivalency of the axial and helical scan modes (AS and HS, respectively) for head computed tomography (CT) using physical image quality measures and artifact indices (AIs). Two 64-row multi-detector row CT systems (CT-A and CT-B) were used for comparing AS and HSs with detector rows of 64 and 32. The modulation transfer function (MTF), noise power spectrum (NPS), and slice sensitivity profile were measured using a CT dose index corresponding to clinical use. The system performance function (SPF) was calculated as MTF2/NPS. The AI of streak artifacts in the skull base was measured using an image obtained of a head phantom, while the AI of motion artifacts was measured from images obtained during the head phantom was in motion. For CT-A, the 50%MTFs were 7% to 9% higher in the HS than the AS, and the higher MTFs of HS associated NPS increases. For CT-B, the MTFs and NPSs were almost equivalent between the AS and HS, respectively. Consequently, the SPFs of AS and HS were nearly identical for both CT systems. For both CT systems, the skull base AI did not differ significantly between AS and HS, while the motion AIs of HS were significantly better than of AS. The superior motion AI in the HS indicated the effectiveness of HS on moving patients.

Radiological classification of retroperitoneal hematoma resulting from lumbar vertebral fracture.

PURPOSE: Lumbar vertebral fracture (LVF) infrequently produces massive retroperitoneal hematoma (RPH). This study aimed to systematically review the clinical and radiographic characteristics of RPH resulting from LVF. METHODS: For 193 consecutive patients having LVF who underwent computed tomography (CT), demographic data, physiological conditions, and outcomes were reviewed from their medical records. Presence or absence of RPH, other bone fractures, or organ/vessel injury was evaluated in their CT images, and LVF or RPH, if present, was classified according to either the Orthopaedic Trauma Association classification or the concept of interfascial planes. RESULTS: RPH resulting only or dominantly from LVF was found in 66 (34.2%) patients, whereas among the others, 64 (33.2%) had no RPH, 38 (19.7%) had RPH from other injuries, and 25 (13.0%) had RPH partly attributable to LVF. The 66 RPHs resulting only or dominantly from LVF were radiologically classified into mild subtype of minor median (n = 35), moderate subtype of lateral (n = 11), and severe subtypes of central pushing-up (n = 13) and combined (n = 7). Of the 20 patients with severe subtypes, 18 (90.0%) were in hemorrhagic shock on admission, and 6 (30.0%) were clinically diagnosed as dying due to uncontrollable RPH resulting from vertebral body fractures despite no anticoagulant medication. CONCLUSIONS: LVF can directly produce massive RPH leading to hemorrhagic death. A major survey of such pathology should be conducted to establish appropriate diagnosis and treatment.

Comparative evaluation of image quality among different detector configurations using area detector computed tomography.

The 320-detector row computed tomography (CT) system, i.e., the area detector CT (ADCT), can perform helical scanning with detector configurations of 4-, 16-, 32-, 64-, 80-, 100-, and 160-detector rows for routine CT examinations. This phantom study aimed to compare the quality of images obtained using helical scan mode with different detector configurations. The image quality was measured using modulation transfer function (MTF) and noise power spectrum (NPS). The system performance function (SP), based on the pre-whitening theorem, was calculated as MTF2/NPS, and compared between configurations. Five detector configurations, i.e., 0.5 × 16 mm (16 row), 0.5 × 64 mm (64 row), 0.5 × 80 mm (80 row), 0.5 × 100 mm (100 row), and 0.5 × 160 mm (160 row), were compared using a constant volume CT dose index (CTDIvol) of 25 mGy, simulating the scan of an adult abdomen, and with a constant effective mAs value. The MTF was measured using the wire method, and the NPS was measured from images of a 20-cm diameter phantom with uniform content. The SP of 80-row configuration was the best, for the constant CTDIvol, followed by the 64-, 160-, 16-, and 100-row configurations. The decrease in the rate of the 100- and 160-row configurations from the 80-row configuration was approximately 30%. For the constant effective mAs, the SPs of the 100-row and 160-row configurations were significantly lower, compared with the other three detector configurations. The 80- and 64-row configurations were adequate in cases that required dose efficiency rather than scan speed.

[Evaluation of low-contrast detectability in low-dose chest computed tomography].

We investigated whether low-contrast resolution evaluation can be applied to chest (lung field) computed tomography (CT) images that are commonly reconstructed using filter kernels with strong frequency emphasis and displayed at wide window widths. We assumed low dose chest CT examinations and set the current-time product to 5 and 10 mAs. The visual detection study was performed by five radiological technologists using water phantom images in which the simulated low contrast objects (disc objects) were implanted. In addition, values of the low contrast detectability index (LCDI) based on a signal-to-noise ratio theorem were calculated from the modulation transfer factor, noise power spectrum, and the object's spectrum for each combination of object size, contrast, current-time product, and kernel. The detectability results correlated well with the LCDI values and correlated less well with the contrast-to-noise ratio results. These results were consistent with the results of past reports on abdomen images. Therefore, our results indicated that low contrast sensitivity can be applied to chest CT images as well as abdominal ones.

[Examination of motion artifacts for helical and non-helical scanning modes in head CT].

For head computed tomography (CT), non-helical scanning has been recommended even in the widely used multi-slice CT (MSCT). Also, an acute stroke imaging standardization group has recommended the non-helical mode in Japan. However, no detailed comparison has been reported for current MSCT with more than 16 slices. In this study, we compared the non-helical and helical modes for head CT, focusing on temporal resolution and motion artifacts. The temporal resolution was evaluated by using temporal sensitivity profiles (TSPs) measured using a temporal impulse method. In both modes, the TSPs and temporal modulation transfer factors (MTFs) were measured for various pitch factors using 64-slice CT (Aquilion 64, Toshiba). Two motion phantoms were scanned to evaluate motion artifacts, and then quantitative analyses for motion artifacts and helical artifacts were performed by measuring multiple regions of interest (ROIs) in the phantom images. In addition, the rates of artifact occurrence for retrospective clinical cases were compared. The temporal resolution increased as the pitch factor was increased. Remarkable streak artifacts appeared in the non-helical images of the motion phantom, in spite of the equivalent effective temporal resolution. In clinical analysis, results consistent with the phantom studies were shown. These results indicated that the low pitch helical mode would be effective for emergency head CT with patient movement.