[Usefulness of Delay Time Setting in Computed Tomography Pulmonary Angiography].

PURPOSE: During computed tomography pulmonary angiography (CTPA), a decrease in the CT value of the pulmonary artery may be observed due to poor contrast enhancement, even though the imaging is performed at the optimum timing while continuously injecting a contrast medium. This study focused on the increase in blood flow in the superior and inferior vena cava during inspiration that affects the decrease in the CT value of the pulmonary artery and investigated a radiography method in which a delay time was set after inspiration in clinical cases. METHODS: A total of 50 patients who underwent CTPA for suspected pulmonary thromboembolism were included. Using the bolus tracking method, we monitored the pulmonary arteries before and after inspiration, and investigated the CT value changes. RESULTS: A decrease in the CT value of the pulmonary artery after inspiration was observed in approximately 30% of cases. By setting the delay time, the contrast enhancement effect before and after inspiration became equivalent. CONCLUSION: As a result of this study, avoiding a decrease in the CT value of the pulmonary artery is possible by setting a delay time after inspiration, which is considered useful during CTPA.

A new shielding calculation method for X-ray computed tomography regarding scattered radiation.

The goal of this study is to develop a more appropriate shielding calculation method for computed tomography (CT) in comparison with the Japanese conventional (JC) method and the National Council on Radiation Protection and Measurements (NCRP)-dose length product (DLP) method. Scattered dose distributions were measured in a CT room with 18 scanners (16 scanners in the case of the JC method) for one week during routine clinical use. The radiation doses were calculated for the same period using the JC and NCRP-DLP methods. The mean (NCRP-DLP-calculated dose)/(measured dose) ratios in each direction ranged from 1.7 ± 0.6 to 55 ± 24 (mean ± standard deviation). The NCRP-DLP method underestimated the dose at 3.4% in fewer shielding directions without the gantry and a subject, and the minimum (NCRP-DLP-calculated dose)/(measured dose) ratio was 0.6. The reduction factors were 0.036 ± 0.014 and 0.24 ± 0.061 for the gantry and couch directions, respectively. The (JC-calculated dose)/(measured dose) ratios ranged from 11 ± 8.7 to 404 ± 340. The air kerma scatter factor κ is expected to be twice as high as that calculated with the NCRP-DLP method and the reduction factors are expected to be 0.1 and 0.4 for the gantry and couch directions, respectively. We, therefore, propose a more appropriate method, the Japanese-DLP method, which resolves the issues of possible underestimation of the scattered radiation and overestimation of the reduction factors in the gantry and couch directions.

Influence of aortic valve leaflet calcification on dynamic aortic valve motion assessed by cardiac computed tomography.

BACKGROUND: Computed tomography is the best noninvasive imaging modality for evaluating valve leaflet calcification. OBJECTIVE: To evaluate the association of aortic valve leaflet calcification with instantaneous valve opening and closing using dynamic multidetector computed tomography (MDCT). METHODS: We retrospectively evaluated 58 consecutive patients who underwent dynamic MDCT imaging. Aortic valve calcification (AVC) was quantified using the Agatston method. The aortic valve area (AVA) tracking curves were derived by planimetry during the cardiac cycle using all 20 phases (5% reconstruction). da/dt in cm2/s was calculated as the rate of change of AVA during opening (positive) or closing (negative). Patients were divided into 3 three groups according to Agatston score quartile: no AVC (Q2, Score 0, n = 18), mild AVC (Q3, Score 1-2254, n = 24), and severe AVC (Q4 Score >2254, n = 14). RESULTS: In multivariable linear regression, compared to the non AVC group, the mild and severe AVC groups had lower maximum AVA (by -1.71 cm2 and -2.25 cm2, respectively), lower peak positive da/dt (by -21.88 cm2/s and -26.65 cm2/s, respectively), and higher peak negative da/dt (by 13.78 cm2/s and 18.11 cm2/s, respectively) (p < 0.05 for all comparisons). CONCLUSIONS: AVA and its opening and closing were influenced by leaflet calcification. The present study demonstrates the ability of dynamic MDCT imaging to assess quantitative aortic valve motion in a clinical setting.

[Usefulness of low kilovoltage settings in computed tomography venography of lower limbs].

It has been reported that a reduction in tube kilovoltage during computed tomography (CT) angiography results in an average reduction of the effective radiation dose. Furthermore, a lower kilovoltage has been shown as a technique dose. However, there is no fundamental data in a low-kilovoltage protocol for CT venography. Thus, the purpose of this study was to investigate contrast enhancement, image noise, and radiation exposure with lower kilovoltage on CT images scanned using phantom of lower limbs and clinical CT images. In order to grasp the effective energy in each tube voltage of the equipment used, we determined the half-value layer using aluminum attenuation coefficient. The phantom of the lower was sealed with contrast agent that was adjusted in various CT values. We scanned this phantom at 80 kVp, 100 kVp, and 120 kVp settings, and evaluated the changes in CT value. We also compared CT values, CTDIvol, contrast enhancement, and radiation exposure with 100 kVp and 120 kVp in patients with suspected pulmonary embolism or deep venous thrombosis. We found the CT value increased 30 HU with 100 kVp settings, and contrast was also improved. A reduction of radiation exposure without deterioration of image quality would be possible by lowering the kilovoltage setting in CT venography.