Magnetization transfer ratios (MTRs) of tissues with different characteristics were investigated. Crossrelaxation rates of solutions with different protein concentrations were studied. We evaluated the MTRs of female breast tumors, the globus pallidus, and nasopharyngeal tumors, and assessed the usefulness of MTRs in determining tissue characteristics. In phantom studies, we measured MTRs using gelatin and MnC12 solution with various concentrations of gelatin and MnC12. MTRs were measured using pairs of images obtained by conventional SPGR sequence and MT - prepared SPGR sequence. MTRs, defined as the percentage of signal loss between unsaturated and saturated images, were calculated using the equation (Mo - Ms) /Mo, where Mo is the measured signal intensity on the conventional SPGR images, and Ms is the measured signal intensity on the MT - prepared SPGR images. We investigated relationships between pathological findings and MTRs of breast tumors, between liver function and MTRs of globus pallidus, and between the DNA index and MTRs of nasopharyngeal tumors. MTRs increased with increased gelatin concentration, but decreased as the MnC1 2 concentration increased. MTRs of breast carcinoma were higher than those of benign tumors. MTRs of globus pallidus showed a correlation with liver function (ChE: r = 0.79, PT: r = 0.75, ICGR15: r 0.98). MTRs of aneuploid nasopharyngeal tumors had high MTRs. MTR is a good indicator of protein concentration and could be a new and useful parameter for tissue characterization.
Narrow photon beam dosimetry used in stereotactic radiosurgery can be made difficult because of the presence of lateral electoronic disequilibrium and steep dose gradiants. Dosimetric characteristics of 10MV circular narrow photon beams ranging in size from 11.6 to 31.4 mm are reported. These characteristics include the measurement of tissue maximum ratio, off axis ratio and relative output factors. Measurements of these parameters were performed in a solid water phantom using x-ray films and cylindrical micro ionization chamber. Although in 50% isodose level width the measurement by micro ionization chamber and x-ray film correlated well, in 80% isodose level width measurement by micro chamber showed apparent underevaluation than that by x-ray film. The relative output factors measurement by micro ionization chamber was consistent with that by x-ray film within 3 % for the field size between 11.6 and 31.4 mm φ.
This study presented a procedure of the quality control of SPECT using analytical SPECT reconstruction methods. These are Fourier domain techniques as described by 1) Bellini et al and 2)Inouye et al. which can invert exactly the attenuated Radon transform by Fourier transforms and series expansions. We implemented these methods on a three-detector SPECT system (Picker Prism 3000 XP STEP) and used the JIS SPECT phantom (Kyoto Kagaku, Japan) and several kinds of phantoms for performance evaluation. Projection data were acquired in 128 x 128 matrix with 3 degree steps over 360 degree circular orbit for total scan time of 20 min. Two energy windows, one at 140keV ± 24% (140keV ± 15%) and other 120keV ± 3% (126keV ± 5%) were used for scatter correction. Attenuation coefficient of water 0.15cm-1 for the 140keV gamma ray of "Tc was used. The computing time was less than 10 sec for one slice of 128×128 matrix, thu s the analytical SPECT reconstruction methods are applicable to routine quality control use.
Quality assurance (QA) and quality control (QC) system is essential to positron emission tomographs (PET) like any other medical apparatus. Although part of QA/QC protocols are established by Japan Industries Association of Radiation Apparatus (JIRA), it is desirable to establish a comprehensive QA system that can cover a wide range of fields including physicists, chemists, medical doctors and technologists. The performance evaluation for PET QA/QC is standardized by National Electrical Manufacturers Association (NEMA), and an international standard of performance evaluation is under discussion by International Electrotechnical Commission (IEC). In Japan, a guideline for positron emission tomographs was published by Japan Radioisotope Association (JRIA) and standardized by JIRA. But there are some differences in methods of measurements and analyses among those publications. There are also QA/QC items which are not handled in the above mentioned guidelines, for example, check of detectors and cross calibration between PET and well counter.
It is absolutely imperative in the clinical field to maintain proper function and performance of medical equipment that meets certain standards while also providing best - quality images and securing safeties for operators. In order to implement these goals, equipment manufacturers and users are required to execute tight quality control of the equipment on each side. Manufacturers have been carrying out QA (quality assurance) and QC (quality control) programs for their products based on their own quality standards for long time, whereas only a portion of users have been conducting their own tests so far. However, recently a broad users' QA & QC movement has started to evolve following activities of the QC group of the JSRT (Japanese Society of Radiological Technology) and the publication of QC programs. I present the analysis of causes of malfunction of CT for the purpose of safety and also describe about QA & QC methods from the user's viewpoint.
Magnetic resonance imaging (MRI) is now widely used in clinical practices. However MR images may be affected by slight changes of machine performances or environmental conditions, and it could cause misdiagnosis in clinical routines. To maintain and assure image quality in clinical routines, performance of MRI system should be evaluated periodically. In this report we described the NEMA (National Electrical Manufactures Association) standard of evaluation methods of MRI system. The standard included determination of signal to noise ratio (SNR),2-dimensional geometric distortion, image uniformity and slice thickness. We also described the JIS (Japanese Industrial Standard) phantom, which was designed to measure the above characteristics as well as spatial resolution of MRI system in quality assurance (QA) programms.