[Development of estimated time of arrival method and usefulness in pulmonary artery/vein separation 3D-CT].

We have developed an estimated time of arrival (ETA) method as a new single-phase scan for pulmonary artery/vein separation. This method enables differentiation of CT values between arteries and veins by means of two-step consecutive injection of contrast medium based on the pulmonary circulation time. This paper presents an overview of the ETA method and scan technique. Since the ETA method is a single-phase scan, it uses a low radiation dose compared with the conventional multi-phase scan. Moreover, this method eliminates gaps due to breath holding. The ETA method can detect irregularities and obtain high-quality pulmonary artery/vein separation 3D-CT images.

CT-fluoroscopy in chest interventional radiology: sliding scale of imaging parameters based on radiation exposure dose and factors increasing radiation exposure dose.

AIM: To verify the usefulness of a sliding scale of imaging parameters to reduce radiation exposure during chest interventional radiology (IR), and to identify factors that increase radiation exposure in order to obtain acceptable computed tomography (CT)-fluoroscopy image quality. MATERIALS AND METHODS: The institutional review board approved this retrospective study, for which the need for informed consent was waived. Interventional radiologists determined the optimal CT-fluoroscopy imaging parameters using the sliding scale based on the radiation exposure dose. The imaging parameters were changed from those generating low radiation (120 kV/10 mA, 1.2 mGy/s) to others generating higher radiation exposure until acceptable image quality was obtained for each procedure. Validation of the imaging parameter sliding scale was done using regression analysis. Factors that increase radiation exposure were identified using multiple regression analysis. RESULTS: In 125 patients, 217 procedures were performed, of which 72 procedures (33.2%, 72/217) were performed with imaging parameters of minimum radiation exposure, but increased radiation exposure was necessary in 145 (66.8%, 145/217). Significant correlation was found between the radiation exposure dose and the percentage achievement of acceptable image quality (R(2) = 0.98). Multivariate regression analysis showed that high body weight (p < 0.0001), long device passage (p < 0.0001), and lesions above the aortic arch (p = 0.04) were significant independent factors increasing radiation exposure. CONCLUSION: Although increased radiation exposure dose might be necessary to obtain acceptable chest CT-fluoroscopy images depending on the patient, lesion, and procedure characteristics, a sliding scale of imaging parameters helps to reduce radiation exposure.

[Partial electrical reset of CT irradiation on implantable cardiac devices: relationship between reset and tube voltage, tube current, and rotation time].

The aim of this study was to investigate the relationship between partial electrical reset (PER) and CT scan parameters (tube voltage, tube current, rotation time, and product of tube current and rotation time in mAs). A cardiac resynchronization therapy pacemaker (Insync 8040, Medtronic Inc., Tokyo) and 320 area detector CT scanner (Aquilion ONE, Toshiba medical systems, Otawara, Japan) with volume scan were used. The pacemaker was put in DDD mode. The PERs were interpreted using both the programmer's wave forms and error messages. The exposure was repeated 5 times per CT setting. The pacemaker was placed on the anterior wall and upper side of a chest phantom. Each CT scan was performed using the following parameters: tube voltage of 80, 100, 120, and 135 kV; tube current of 50-550 mA; and rotation time of 0.35-1.5 s. PERs were observed at 100, 120, and 135 kV, and more PERs were observed as the tube voltage increased. The PER tube current decreased as the rotation time was increased. In contrast, the PER tube current and rotation time product (mAs) increased as the rotation time was increased. More specifically, the radiation dose rate was the affected factor of the PERs. To avoid PER of pacemakers, CT scan parameters with lower radiation dose rates (low rather than high tube current and rotational time) is recommended. In conclusion, our results will help with CT scans of patients who have implantable cardiac devices (included pacemakers and cardioverter defibrillators).

Optimal scan parameters for CT fluoroscopy in lung interventional radiologic procedures: relationship between radiation dose and image quality.

PURPOSE: To evaluate the relationship between radiation doses and lung computed tomographic (CT) fluoroscopic scan parameters and to determine optimal scan parameters for performance of lung interventional radiologic (IR) procedures. MATERIALS AND METHODS: The institutional review board approved this prospective study, which included 32 patients with a single lung tumor; written informed consent was obtained. CT fluoroscopic images were obtained with three tube voltages (80,120,135 kV) and three tube currents (10, 20, 30 mA) in each patient. The signal-to-noise ratios (SNRs) and the contrast-to-noise ratios (CNRs) were measured quantitatively. To evaluate the feasibility of performing lung IR procedures, four readers visually scored the image quality. Acceptable CT fluoroscopic images were determined by using agreement of at least three of the four readers. The weighted CT dose index for each CT scan parameter was measured. A piecewise linear regression equation was obtained from the relationship between radiation doses and visual image scores. RESULTS: Both the SNR and the CNR improved as the radiation dose increased, leading to improvement in the image quality. Acceptable image quality was achieved in 94% (30 of 32) of patients when the radiation dose was 1.18 mGy/sec (120 kV, 10 mA) and in all patients when it was greater than 1.48 mGy/sec (135 kV, 10 mA). The piecewise linear curve showed rapid improvement in image quality until the radiation dose increased to 1.48 mGy/sec (135 kV, 10 mA). When the radiation dose was increased greater than 1.48 mGy/sec, improvement in the image quality became more gradual. CONCLUSION: Results of this study can be used to guide the determination of optimal scan parameters in lung CT fluoroscopy.