In medical linear accelerators, radioactivation is induced on the target and neighborhood parts by photoneutrons accompanying a photo-nuclear reaction and leading to higher acceleration energy. We measured the residual radiation from the radioactivated materials according to the time, and tried to identify radioactivated nuclides and their relative quantities by means of measurement results. It was presumed that the main source of residual radiations was the Target, Flattening filter and Primary collimator in the linac head. Among those materials (copper, tungsten), we calculated decrement curves of residual radiations from radioactivated nuclides generated with photo-nuclear reaction or thermal neutron capture reaction by various ratios, and we investigated the ratio that best fit the measured data. Consequently, it was presumed that 66Cu generated with thermal neutron capture reaction contributed the most to residual radiation, followed by 62Cu generated with photo-nuclear reaction contributed. It is important to understand various characteristics of these nuclides and to undertake management of the device.
The aim of this study was to evaluate the usefulness of the collimator detector response (CDR) recovery and the effective scatter source estimation (ESSE) method which is the scatter correction method built into the ordered subsets expectation maximization (OSEM) method. Method: The SPECT quality evaluation phantom and the anthropomorphic torso phantom were used in this study, and image contrast and uniformity were evaluated. The effect of each image correction method on the quantification of absolute radioactivity was also assessed. Results and Conclusion: Image contrast and uniformity were improved with the combination of the CDR recovery and triple energy window (TEW) method or the ESSE method. The combination of the CDR recovery and the ESSE method was the best method for the estimation of absolute radioactivity. Image quality of the SPECT is improved by the combination of CDR recovery and scatter correction in addition to attenuation correction. CDR recovery in addition to attenuation and scatter correction is also useful for the quantification of absolute radioactivity.
Flow-sensitive alternating inversion recovery (FAIR), which is an excellent method of non-invasive assessment of cerebral blood flow (CBF), was applied to brain function. Because blood oxygenation level dependent (BOLD) is an established method at present, brain functional imaging by FAIR was compared with BOLD. A few minutes is the necessary scanning time in FAIR targeted for brain ischemia. For BOLD, however, scanning time in a state is several seconds. A method of improving problems with scanning time was examined. There was no problem about the stability of the signal when scanning in design method, and a similar signal change was able to be confirmed. Additionally, there was no difference between each method concerning the activated part (p > 0.05). However, the activated area in FAIR was smaller than in BOLD (p < 0.01). Brain functional imaging by FAIR offers fewer advantages than BOLD. Yet it seems that reliability increases when measurements are made by the two methods using different mechanisms.
A magnetic resonance imaging (MRI) system compatible linear stage was developed. The stage was made of acrylic plastic and moving power was applied by an ultrasonic motor. Moving distance of the stage was detected by counting the number of motor rotations using a optic fiber sensor. Accuracy and precision of the stage control were measured inside and outside the magnet using a micrometer and a laser distance meter. As a result, a value of more than 95% was achieved in both of them in the 1.5 T magnetic field when it was applied for more than a 0.3 mm movement. Measurement of the slice sensitivity profile (SSP) by the delta method was performed. Slice selection by this linear stage and by radio frequency (RF) offset were compared. The result by linear stage was in good agreement with the result by RF offset. With this linear stage, a performance evaluation test of MRI equipments that need micromotion can be performed.
The high convenience of data collection by helical scanning, such as making multi planner reformat (MPR) and shortening scan time, means that the technique is widely used to diagnose various body parts. However, non-helical scanning is still a main current for plane brain computed tomography. The possibility of diagnosing acute cerebral infarction by helical scanning MPR was examined. It was found that image degradation in helical scanning had little influence on the physical evaluation of the characteristics of modulation transfer function and the noise power spectrum, etc. In the evaluation of the ischemic change occurring at the early stage made by examination of clinical images, the result was almost equal to that obtained by non-helical scanning, as the reported sensitivity was 52% and the specificity was 95%. This suggested that brain helical scanning MPR might be applied clinically. However, a disadvantage was confirmed as helical scanning had a higher exposure dose than non-helical scanning at the start and end of scanning. The results of this study indicated that helical scanning demonstrates sufficient convenience for the assessment of acute cerebral infarction at the basal nucleus level.
Purpose: On coronary MR angiography (CMRA), cardiac motions worsen the image quality. To improve the image quality, detection of cardiac especially for individual coronary motion is very important. Usually, scan delay and duration were determined manually by the operator. We developed a new evaluation method to calculate static time of individual coronary artery. Methods and Materials: At first, coronary cine MRI was taken at the level of about 3 cm below the aortic valve (80 images/R-R). Chronological change of the signals were evaluated with Fourier transformation of each pixel of the images were done. Noise reduction with subtraction process and extraction process were done. To extract higher motion such as coronary arteries, morphological filter process and labeling process were added. Using these imaging processes, individual coronary motion was extracted and individual coronary static time was calculated automatically. We compared the images with ordinary manual method and new automated method in 10 healthy volunteers. Results: Coronary static times were calculated with our method. Calculated coronary static time was shorter than that of ordinary manual method. And scan time became about 10% longer than that of ordinary method. Image qualities were improved in our method. Conclusion: Our automated detection method for coronary static time with chronological Fourier transformation has a potential to improve the image quality of CMRA and easy processing.
Purpose: To discuss the circumstances of patient skin injury in cardiac interventional radiology (IVR). · To demonstrate the importance of evaluating the patient radiation dose in IVR. · To show the need for the appropriate patient follow-up after IVR to identify radiation effects. · To highlight the incidence of skin injuries during IVRs. CONTENT ORGANIZATION: · Evaluation of 400 consecutive percutaneous coronary interventions (PCIs) The radiation dose, number of cine runs, and fluoroscopic time were recorded for all patients. The skin on the patients’ backs was reviewed periodically after PCI to identify radiation injury. The relationships between patient skin effects and factors such as the radiation dose were investigated. · Reviewing previous reports of patient radiation injury Occurrence rate, fluoroscopic time, radiation dose (if available), etc. SUMMARY: Although increasing numbers of case reports of patient radiation injury resulting from IVR are being published, these reports likely represent a small fraction of actual cases. Radiation skin injury in IVR is overlooked clinically in many patients. Patients who receive a high radiation dose while undergoing IVR should be followed to identify radiation skin effects, and physicians should seek to establish whether a patient has had previous IVR, together with the entrance site and radiation dose.
Purpose: The aim of our study was to evaluate the image quality of multiplanar reconstruction images (MPRs) focusing on the effect of z-increment of original axial images using signal to noise ratio (SNR) measurement in in- plane and longitudinal directions. METHODS AND MATERIALS: SNRs of MPRs were calculated using modulation transfer function (MTF) and noise power spectrum (NPS). We scanned a bead phantom with a diameter of 0.1 mm and a water phantom with a diameter of 250 mm for calculating MTF and NPS using a MDCT with 0.5 s per rotation, 1.0 pitch and 64 × 0.6 mm collimation, and 50 mm field of view. Axial images for generating MPRs were reconstructed with standard kernel (B40), and 1.00 mm slice width. Coronal images were generated from two datasets with 0.1 mm and 0.5 mm z-increments of axial images respectively. For measuring the SNRs, the MTFs and NPSs in in-plane and longitudinal directions of each dataset were calculated from coronal bead images and coronal uniform noise images, respectively. Differences of MTF, NPS, and SNR were compared in in-plane and longitudinal directions. RESULTS: The MTF of longitudinal direction of the dataset with 0.1 mm z-increment was higher than the dataset with 0.5 mm z-increment. 10% MTFs of longitudinal direction with 0.1 mm and 0.5 mm z-increments were 0.75 cycles/mm and 0.68 cycles/mm, respectively. Conversely, the NPS of longitudinal direction of the dataset with a 0.1 mm z-increment was lower than the dataset with a 0.5 mm z-increment. As a consequence, the SNRs of longitudinal direction had relatively no difference between the datasets. In in-plane direction, MTFs, NPSs and SNRs had no differences between the datasets. CONCLUSION: A tradeoff relationship was indicated between spatial resolution and noise characteristic in the longitudinal direction due to the effects of different z-increment of original axial images used in generating MPRs. MPR using 0.5 mm z-increment of axial images had comparable SNR to MPR using 0.1 mm z-increment of axial images in our experimental condition. CLINICAL RELEVANCE/APPLICATION: Using 0.5 mm z-increment of original axial images for generating MPRs is effective for reducing the data volume, reconstruction time and transfer time without reducing image quality.
Purpose: To evaluate whether a comprehensive image processing method as CAD using CT and MRI can improve the radiologists’ diagnosis performance in the differentiation of focal liver lesions. METHOD AND MATERIALS: A clinical image database used in this study consists of 14 cases of each lesion including hepatic cysts, hepatocellular carcinoma (HCC), metastatic liver cancer, and hemangioma. This technique by using MR images obtained with various imaging sequences and a series of dynamic MR and dynamic CT images is designed for the enhancement of liver lesions pixel by pixel. In this method, we make the pixel sizes of MR images the same size of CT image by using tri-linear interpolation technique. Then the 3D image registration technique based on mutual information is applied for the matching of images. The image intensity pattern with and without contrast enhancement is determined as the template for the differential detection of each lesion. Pixel-by-pixel cross-correlation coefficient is calculated for the enhancement of each lesion. The radiologists’ performance in distinguishing between the liver lesion was evaluated by receiver operating characteristic analysis (ROC) with a continuous rating scale. RESULTS: In free-response ROC analysis, true positive fractions were 75%, 87%, 85%, and 86% for hepatic cysts, HCC, metastatic liver cancer and hemangioma, respectively. Furthermore, average number of false positive and false negatives per image was 3.4 and 0.3, respectively. When radiologists made differential diagnosis of the liver lesions with the images of this technique, diagnostic accuracy was statistically significantly improved compared to the diagnostic accuracy without the images of this technique. The average area under the ROC curve (Az value) improved from 0.881 to 0.964 (p=0.069) for the differential diagnosis of hepatic cysts. Furthermore, the Az value of HCC, metastatic liver cancer, and hemangioma improved from 0.951 to 0.979 (p=0.040), from 0.946 to 0.976 (p=0.226), and from 0.966 to 0.987(p=0.045), respectively. CONCLUSION: A comprehensive image processing method as CAD using CT and MRI can improve the radiologists’ diagnostic performance in the differentiation of focal liver lesions. CLINICAL RELEVANCE/APPLICATION: This method improved the performance of differential detection of liver lesions from a large number of images and it would save radiologists’ reading time, and thus could assist their diagnosis.