Pulmonary artery flow velocity, flow volume and their derived biomarkers, such as acceleration time (AT), acceleration volume (AV) and peak velocity (PV), vary depending on the severity and type of pulmonary disease. Therefore, accurate measurements of pulmonary artery velocity are very important for assessing the severity of pulmonary disease. The purpose of this study was to optimize the imaging parameters for pulmonary artery flow velocity using 3D cine PC MR, and to evaluate AT, AV, and PV for pulmonary hypertension. We changed the flip angle (FA) and view per segment (VPS). FA influenced the signal intensity, which was calculated from the magnitude images. Smaller VPS improved the accuracy of PV. Consequently, optimal setting of FA and VPS was important for hemodynamic analysis. We established the optimal FA and VPS for use in the hemodynamic analysis. AV and PV at the right pulmonary artery differed significantly between healthy volunteers and patients with pulmonary hypertension. Hemodynamic analysis of 3D cine PC MR imaging was considered promising for the evaluation of pulmonary disease.
Purpose: Volumetric modulated arc therapy (VMAT) is a rotational intensity-modulated radiotherapy (IMRT) technique capable of acquiring projection images during treatment. The purpose of this study was to reconstruct the dose distribution from respiratory signals and machine parameters acquired during stereotactic body radiotherapy (SBRT). Methods: The treatment plans created for VMAT-SBRT included the constraint of 1 mm/degree in multileaf collimator (MLC) for a moving phantom and three patients with lung tumors. The respiratory signals were derived from projection images acquired during VMAT delivery, while the machine parameters were derived from machine logs. The respiratory signals and machine parameters were then linked along with the gantry angle. With this data, the dose distribution of each respiratory phase was calculated on the planned four-dimensional CT (4D CT). The doses at the isocenter, the point of max dose and the centroid of the target were compared with those of the corresponding plans. Results and discussion: In the phantom study, the maximum dose difference between the plan and “in-treatment” results was −0.4% at the centroid of the target. In the patient study, the difference was −1.8 ± 0.4% at the centroid of the target. Dose differences of the evaluated points between 4 and 10 phases were not significant. Conclusion: The present method successfully reconstructed the dose distribution using the respiratory signals and machine parameters acquired during treatment. This is a feasible method for verifying the actual dose for a moving target.
Objective: The present study aimed at determining the quantitative accuracy of phase-based respiratory-gated PET/CT imaging using phantom and clinical studies. Methods: The effects of target size, target-to-background ratio (TBR), and respiratory motion on PET images were estimated using a NEMA body phantom comprising six spheres (diameter 10–37mm) in a solution of F-18 of three different TBRs (4, 6, 8). The phantom was moved in a superior-inferior direction at motion displacements of 0, 10, 20 and 30 mm. Stationary images of the phantom as well as non-gated (3D) and gated (4D) images of the phantom while moving were reconstructed and the recovery coefficient (RC) of individual spheres was calculated from each image. We then determined the RC improvement rate to evaluate improvements conferred by 4D-PET/CT. We retrospectively analyzed data from 14 patients with lung cancer who were examined by 3D- and 4D-PET/CT. Each lesion on the 3D-PET/CT and each of the five phases of the 4D-PET/CT were analyzed. Results: Larger motion displacement and TBR resulted in increased RC degradation for small spheres. The RC improvement rate showed that 4D acquisition improved the RC of spheres with larger motion displacement exceeding 13 mm in diameter. 4D-PET/CT alone can reduce the effects of motion blurring, but partial volume effects may still be the dominant source of quantitative inaccuracy for small lesions. The trends of phantom and clinical studies for evaluating the improvement rate were similar. Conclusions: 4D-PET/CT significantly improved the quantitative accuracy of PET images particularly when larger motion displacement exceeded 17mm in diameter such as in lung cancer.
Purpose: The aim of this study was to find the optimal acquisition parameters of non-contrast-enhanced non-breath-holding pulmonary artery MRA using 3D-FSE imaging with variable flip angle echo trains. Materials and Methods: The 3D-FSE imaging method with variable flip angle echo trains (CUBE) was employed in this study. Pulmonary artery MRA was performed in five healthy volunteers using a 1.5 tesla (T) and a 3 T clinical scanner with multi-channel torso coils. The institutional review boards approved the study, and informed consent was obtained from all subjects. Prior to the CUBE studies, ECG-gated single-shot FSE scans were performed to determine the timing of systole and diastole. After that, CUBE scans with systolic timing and three adjusted (early, middle and delayed) diastolic timings using both ECG and respiratory gating were performed and subtracted images between systolic and diastolic images were calculated. Subtracted intensities of both lung parenchyma and pulmonary arteries were evaluated using the region of interest (ROI) function. Maximum intensity projection (MIP) images with six different scan parameters (three timings and two static magnetic fields) were processed for evaluation by the ranking method with visual assessment. Three observers each scored all six images and a statistical analysis based on the variation of ratings was performed. Results: The subtracted intensities of pulmonary arteries and lung parenchyma with middle diastolic timing were higher than that with both early and delayed systolic timing. The same tendency was shown in both 1.5 T and 3 T images. Though the subtracted intensity of 3 T was higher than that of 1.5 T, the contrast ratio between lung parenchyma and pulmonary artery of 1.5 T was higher than that of 3 T. The MIP image using the 1.5 T scanner with middle diastolic timing obtained the best score by the visual assessment using the ranking methods. The middle diastolic timing using the 1.5 T scanner provides the best non-contrast-enhanced non-breath-holding pulmonary artery MRA.
With the digitization of general radiography, there are some concerns about an increase in radiation exposure doses. Therefore, the exposure index (EI) as a new dose index was proposed in 2008 by IEC. However, the settings for the interest region and the interest value in the clinical image do not show concrete prescribed values. Therefore, we inspected the distribution of EI by changing the interest region and the interest value for a standing-position chest radiograph image in students’ medical examinations. EI50f, which is generally used, fluctuated between 41 and 136. In addition, as the area of the interest region became smaller, EI increased and the variation index increased. For the interest value, 50% (EI50h) was smaller than 85% (EI85h), and the variation index was also smaller. EI was not the absolute value in the clinical image, and immediate display of the deviation index (DI) with target exposure index (EIT) was effective of the adequacy of the radiography condition.
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.
To investigate the optimal beam quality for chest computed radiography (CR), we measured the radiographic contrast and evaluated the image quality of chest CR using various X-ray tube voltages. The contrast between lung and rib or heart increased on CR images obtained by lowering the tube voltage from 140 to 60 kV, but the degree of increase was less. Scattered radiation was reduced on CR images with a lower tube voltage. The Wiener spectrum of CR images with a low tube voltage showed a low value under identical conditions of amount of light stimulated emission. The quality of chest CR images obtained using a lower tube voltage (80 kV and 100 kV) was evaluated as being superior to those obtained with a higher tube voltage (120 kV and 140 kV). Considering the problem of tube loading and exposure in clinical applications, a tube voltage of 90 to 100 kV (0.1 mm copper filter backed by 0.5 mm aluminum) is recommended for chest CR.
The performance of individual computed tomography automatic exposure control (CT-AEC) is very important for radiation dose reduction and image quality equalization in CT examinations. The purpose of this study was to evaluate the performance of CT-AEC in conventional pitch mode (Normal spiral) and fast dual spiral scan (Flash spiral) in a 128-slice dual-source CT scanner. To evaluate the response properties of CT-AEC in the 128-slice DSCT scanner, a chest phantom was placed on the patient table and was fixed at the center of the field of view (FOV). The phantom scan was performed using Normal spiral and Flash spiral scanning. We measured the effective tube current time product (Eff. mAs) of simulated organs in the chest phantom along the longitudinal (z) direction, and the dose dependence (distribution) of in-plane locations for the respective scan modes was also evaluated by using a 100-mm-long pencil-type ionization chamber. The dose length product (DLP) was evaluated using the value displayed on the console after scanning. It was revealed that the response properties of CT-AEC in Normal spiral scanning depend on the respective pitches and Flash spiral scanning is independent of the respective pitches. In-plane radiation dose of Flash spiral was lower than that of Normal spiral. The DLP values showed a difference of approximately 1.7 times at the maximum. The results of our experiments provide information for adjustments for appropriate scanning parameters using CT-AEC in a 128-slice DSCT scanner.
The purpose of this study was to evaluate the radiation dose reduction to patients and radiologists in computed tomography (CT) guided examinations for the thoracic region using CT fluoroscopy. Image quality evaluation of the real-time filtered back-projection (RT-FBP) images and the real-time adaptive iterative dose reduction (RT-AIDR) images was carried out on noise and artifacts that were considered to affect the CT fluoroscopy. The image standard deviation was improved in the fluoroscopy setting with less than 30 mA on 120 kV. With regard to the evaluation of artifact visibility and the amount generated by the needle attached to the chest phantom, there was no significant difference between the RT-FBP images with 120 kV, 20 mA and the RT-AIDR images with low-dose conditions (greater than 80 kV, 30 mA and less than 120 kV, 20 mA). The results suggest that it is possible to reduce the radiation dose by approximately 34% at the maximum using RT-AIDR while maintaining image quality equivalent to the RT-FBP images with 120 V, 20 mA.
Magnetic resonance imaging (MRI) enables the evaluation of organ structure and function. Oxygen-enhanced MRI (O2-enhanced MRI) is a method for evaluating the pulmonary ventilation function using oxygen as a contrast agent. We created the Cine View of Relative Enhancement Ratio Map (Cine RER map) in O2-enhanced MRI to easily observe the contrast effect for clinical use. Relative enhancement ratio (RER) was determined as the pixel values of the Cine RER map. Moreover, six healthy volunteers underwent O2-enhanced MRI to determine the appropriate scale width of the Cine RER map. We calculated each RER and set 0 to 1.27 as the scale width of the Cine RER map based on the results. The Cine RER map made it possible to observe the contrast effect over time and thus is a convenient tool for evaluating the pulmonary ventilation function in O2-enhanced MRI.
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.
Along with the increase in regularly scheduled pulmonary check-ups, there has also been an increase in the detection of nodules smaller than 20 mm. The differentiation of benign or malignant nodules is reportedly facilitated by adding contrast-enhanced MRI to high-resolution CT. However, there are few studies on peripheral pulmonary nodules smaller than 20 mm. We examined the use of contrast-enhanced MRI for peripheral pulmonary nodules smaller than 20 mm that were difficult to differentiate between benign or malignant using high-resolution CT, and compared the results with the pathological views of the excised specimens. On the time-intensity curve in the dynamic study, we classified it as “steep type”, “flat type”, “gradual type”, and “not visible”. The result was low. As for 75% of sensitivity, 42.9% of specificity, 68.6% of accuracy. However, as for 85.7% of sensitivity, 100% of specificity, 86.7% of accuracy in nodules with less than more than 15mm and 20mm of greatest dimension. The differentiation of benign or malignant nodules smaller than 15 mm is difficult by dynamic MRI, but it appears that MRI facilitates the diagnosis of nodules larger than 15 mm.
Purpose: Although image-guided radiotherapy (IGRT) is widely used to determine and correct daily setup errors, the additional interpretation for image registration would provide another error. We evaluated the uncertainty in image registration in IGRT. Method: The subjects consisted of 12 consecutive patients treated with IGRT for thoracic esophageal cancer. Two radiation therapists had consensually achieved daily 3D registration between planning computed tomography (CT) and cone beam CT (CBCT). The original data sets of image registration in all fractions except for boost irradiations with a change in the isocenter positions were selected for evaluation. There were 20 to 32 data sets for each patient: a total of 318 data sets. To evaluate daily setup errors, the mean 3D displacement vector was calculated for each patient. To assess the reproducibility of image registration, two other radiation therapists reviewed the data sets and recorded geometric differences as uncertainty in the image registration. Results: The mean 3D displacement vector for each patient ranged from 4.9 to 15.5 mm for setup errors and 0.7 to 2.2 mm for uncertainty in image registration. There was a positive correlation between the 3D vectors for setup error and uncertainty in image registration (r = 0.487, p = 0.016). Conclusion: Although IGRT can correct the setup errors, potential uncertainty exists in image registration. The setup error would disturb the image registration in IGRT.