Where should we measure the entrance air kerma rate during acceptance testing of the automatic dose control of a fluoroscopic system?

In Japan, the entrance air kerma rate (EAKR) to a patient cannot exceed 50 mGy/min in conventional fluoroscopy. However, it is unclear where the EAKR should be measured. We obtained the tube potential and tube current as a function of polymethylmethacrylate (PMMA) thickness, and the EAKR at the interventional reference point (IRP) was measured from the trajectory. The EAKR at the point established by the U.S. Food and Drug Administration (FDA) was calculated from EAKR at the IRP. The EAKR at the IRP exceeded the limit at a PMMA thickness of 22-28 cm. However, the EAKR did not exceed the limit at the FDA point. If the EAKR to a patient is being verified to meet the recent Japanese ruling, the EAKR should be measured at the FDA point, and if the EAKR is being evaluated for determination of the skin dose, it should be monitored at the IRP. © 2013 Japanese Society of Radiological Technology and Japan Society of Medical Physics

Improvement on detectability of early ischemic changes for acute stroke using nonenhanced computed tomography: Effect of matrix size

京都市立病院金沢大学医薬保健研究域保健学系Purpose: It has recently been reported that intravenous recombinant tissue plasminogen activator improves the clinical outcome after acute stroke. Computed tomography (CT) is the standard imaging method used to determine the indication for thrombolysis. However, detection of early ischemic change often results in an increase in local radiation exposure. Therefore, the effects of decreased matrix size and use of a noise reduction filter were evaluated. Materials and methods: The low contrast resolution was compared for different matrix sizes and imaging filters using a contrast-detail phantom. In addition, early ischemic change in clinical images with matrix sizes of 256 × 256 and 128 × 128 processed using three imaging filters (Gaussian, smoothing, and unsharp mask) from 11 patients within 3 h of stroke onset was evaluated by seven radiologists in a blind manner. Results: The use of images with a matrix size of 256 × 256 and processed with the Gaussian filter increased the detection of early signs of acute stroke. Conclusions: This study was performed to determine whether the converted matrix size and use of imaging filters could improve the detectability of early ischemic change on CT images in acute stroke. To reduce the dose of radiation exposure for patients, it was effective to use an optimal noise reduction filter and reasonable matrix size. In particular, changing the matrix size to 256 × 256 was the most effective for detection of early ischemic change in examinations using clinical images. © 2009 Elsevier Ireland Ltd. All rights reserved

The Effect of Susceptibility of Gadolinium Contrast Media on Diffusion-weighted Imaging and the Apparent Diffusion Coefficient

京都市立病院金沢大学医薬保健研究域保健学系Rationale and Objectives: The development of parallel magnetic resonance imaging has resulted in the frequent use of diffusion-weighted imaging (DWI) in clinical medicine, which usually involves the use of contrast medium. However, gadolinium (Gd) contrast medium may have some effect on DWI and the apparent diffusion coefficient (ADC). The present study was performed to determine whether the magnetic susceptibility of contrast medium alters the DWI signal and the value of ADC in some imaging techniques. Materials and Methods: Nonfat suppression DWI, short-time inversion recovery (STIR) combination, and chemical shift selective (CHESS) combination DWI were performed to examine 10 phantoms with gadolinium-meglumine gadopentetate (Gd-DTPA) dissolved at concentrations from 0.0005 to 0.1 mmol in physiologic saline as a contrast medium. The average pixel value and ADC of each method were determined. Results: ADC showed no differences between before and after treatment with contrast medium for all imaging techniques with Gd considered distributed over the whole tumor. The signal intensity did not change on nonfat suppression or CHESS combination DWI, but deteriorated on STIR. Conclusions: ADC was not influenced by the magnetic susceptibility of contrast medium. In addition, it was suggested that the ability of tumor detection may be reduced if STIR is used as fat suppression. © 2008 AUR

Effects of Iodinated Contrast Agent on Diffusion Weighted Magnetic Resonance Imaging

京都市立病院金沢大学医薬保健研究域保健学系Rationale and Objectives: To evaluate the effects of iodine contrast agent on diffusion signal intensity and apparent diffusion coefficient (ADC) in diffusion-weighted imaging (DWI) studies in magnetic resonance imaging (MRI) examination just after computed tomography (CT) contrast imaging. Materials and Methods: On a 1.5 T MRI scanner, ADC was calculated from the signal intensity of DWI (b = 0 and 1000) using phantoms filled with contrast agent (0, 4.5, 6.0, 9.0, 30, and 60 mgI/mL). We evaluated the signal intensities of DWI and ADC in 10 patients (3 women, 7 men, 35-68 years old) examined by MRI study less than 40 minutes after injection of 100 mL of iopamidol (300 mgI/mL) for CT study. Results: The DWI signal increased until a CT value of 190 HU, but showed no changes above this value. The ADC decreased with increases in CT value. Less than 40 minutes after injection of iopamidol (300 mgI/mL) for CT scan, the signal intensity of DWI was significantly increased and ADC was significantly decreased. Conclusions: It is necessary to recognize the rate of decrease of ADC, because it is dependent on the density of iodine contrast agents. © 2009 AUR

Imaging parameter effects in apparent diffusion coefficient determination of magnetic resonance imaging

金沢大学医薬保健研究域保健学系京都市立病院Purpose: Although an apparent diffusion coefficient (ADC) value is often used for differential diagnosis of tumours, it varies with scanning parameters. The present study was performed to investigate the influence of imaging parameters, i.e., b value, repetition time (TR) and echo time (TE), on ADC value. Methods: The phantoms were scanned using diffusion weighted imaging (DWI) with changing b values (b = 0-3000 s/mm2), TR and TE to determine the influence on ADC. Moreover, ADC of the brain in normal volunteers was determined with varying b values (b = 0-1000 s/mm2). Results: Diffusion decay curves were obtained by biexponential fitting in all phantoms. The points where fast and slow components of the biexponential decay crossed were called turning points. The b values of turning points that crossed from the biexponential curve were different in each phantom. The b values of turning points depended on ADC of fast diffusion component. When ADC is calculated using two b values of front and back for the turning point, the ADC value may be different. Therefore, it was necessary to perform calculations by b value until the turning point to obtain the ADC value of the fast component. In addition, b ≥ 100 was recommended to avoid the influence of perfusion by blood. Furthermore, the choice of long TR and short TE was effective for accurate measurement of ADC. Conclusion: It is important to determine the turning point for measuring ADC. © 2009 Elsevier Ireland Ltd. All rights reserved

Measurement of gantry rotation time in modern ct

The purpose of this study was to develop and evaluate a noninvasive method to assess rotation time in modern commercial computed tomography (CT) systems. The rotation time was measured at a selected nominal rotation time (400 ms) utilizing two types of solid-state detectors: the RTI\u27s CT Dose Profiler (CTDP) and Unfors\u27 Xi (Xi) probes. Either CTDP or Xi was positioned on the inner cover of the gantry and a sheet of lead (1 mm thick) placed on top of the detector. Since a pair of two successive peaks is used to determine the gantry rotation time, by necessity the helical scan must be employed. Upon completion of the data acquisition, these peak times were determined with the dedicated software to obtain rotation time. The average rotation time obtained with CTDP and Xi operated under the dedicated software was found to be 400.6 and 400.5 ms, respectively. The detector for this measurement need not be specifically designed for CT dosimetry. The measurements of CT scanner rotation time can be accomplished with a radiation probe designed for the CT application or a conventional radiation probe designed for radiography and fluoroscopy applications. It is also noteworthy to point out that the measurement results are in good agreement between the two radiation detector systems. Finally, clinical medical physicists should be aware of the accuracy and precision of gantry rotation time, and take into consideration for QA where and when applicable.PACS number: 87.57.Q

A method for assessing metabolic information on liver and bone marrow by use of double gradient-echo with spectral fat suppression

Our aim in this study was to create a noninvasive and practical method for evaluating metabolic information on the liver (iron content and lipid infiltration) and spine (bone mineral density and marrow fat degeneration) using double gradient-echo with and without the spectral fat suppression technique (double-GRE-FS). We arranged phantoms made of various concentrations of superparamagnetic iron oxide solution adjacent to neutral fat to obtain slice planes with various fat fractions using the partial volume effect. We obtained double-GRE-FS images and calculated the T2* values. The fat fraction was calculated from signal intensities of double-GRE-FS images after T2* decay, baseline, and slope corrections. We assessed the fat fraction and the relationship between R2* of the water component and the iron concentration. In addition, we evaluated those values in human bone marrow and liver, including a patient with liver steatosis. The actual fat fraction value was consistent with the fat fraction obtained with the double-GRE-FS method, and the calculated fat fraction was unaffected by the iron concentration. There was a strong positive correlation between R 2* of the water component and the iron concentration. There was a negative correlation between the fat fraction and the bone mineral density, and the R2* was correlated with the bone mineral density. The calculated fat fraction in the liver steatosis patient was significantly higher than that in healthy volunteers. The double-GRE-FS makes it possible to assess the fat fraction and R2* simultaneously, and to obtain metabolic information on the liver and bone marrow. © 2014 Japanese Society of Radiological Technology and Japan Society of Medical Physics

Differentiation of hepatic tumors by use of image contrast with T2-weighted MRI

金沢大学医薬保健研究域Differentiation of hepatic tumors is often evaluated in terms of qualitative diagnostic performance. The signal intensity patterns of hepatic masses are known to differ on certain T2-weighted imaging sequences. In this study, we investigated the quantitative analysis of hepatic masses by using an index called the "T2-shine ratio." Fast-spin-echo (FSE), half-Fourier acquisition single-shot turbo spin echo (HASTE), and true-FISP sequences obtained with quick-imaging techniques during a single breath-hold were examined in 74 patients. T2-shine ratios were calculated by use of the signals of regions of interest (ROIs) placed on a tumor and peripheral tissue: the T2-shine ratio is defined as (tumor signal-liver signal)/liver signal. The rate of change in the T2-shine ratio was compared among three sequences of FSE, HASTE, and true-FISP. The T2-shine ratio of FSE deducted from HASTE was significantly higher for hepatic cysts than for other masses. The T2-shine ratio of HASTE deducted from True-FISP was less than zero for hemangioma. For the value that deducted the T2-shine ratio of HASTE from the T2-shine ratio of true-FISP, hemangiomas had a significantly lower value than did cysts and metastases (P < 0.05), but there was no significant difference from hepatocellular carcinomas (HCCs). Although liver cysts, cavernous hemangiomas, and other lesions could be differentiated, it was virtually impossible to distinguish HCCs from metastatic tumors. In conclusion, the quantitative analysis of hepatic tumors was able to differentiate among these lesions by use of the T2-shine ratio. © 2008 Japanese Society of Radiological Technology and Japan Society of Medical Physics

Qualitative near-infrared vascular imaging system with tuned aperture computed tomography

We developed a novel system for imaging and qualitatively analyzing the surface vessels using nearinfrared (NIR) radiation using tuned aperture computed tomography (TACT®). The system consisted of a NIRsensitive CCD camera surrounded by sixty light emitting diodes (with wavelengths alternating between 700 or 810 nm). This system produced thin NIR tomograms, under 0.5 mm in slice thickness. The venous oxygenation index reflecting oxygen saturation levels calculated from NIR tomograms was more sensitive than that from the NIR images. This novel system makes it possible to noninvasively obtain NIR tomograms and accurately analyze changes in oxygen saturation. © 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).Thesis of Matsushita, Tatsuhiko / 松下 達彦 博士学位論文(金沢大学 / 大学院医薬保健学総合研究科