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Biomedical subjects

R L Morin

Publications and source records attributed to R L Morin.

48 records · Page 3Linked to original sources
PubMedDate not supplied

Evaluation of a multicrystal gamma camera and rotating chair for tomographic studies of the heart.

BACKGROUND: This study evaluates the feasibility of performing tomographic studies with a multicrystal gamma camera combined with a rotating chair. METHODS AND RESULTS: Tomographic acquisitions were performed with a cardiac phantom containing eight defects of different sizes. Defect size was determined from the fraction of counts in the short-axis slices that fell below a fixed threshold value. Image contrast was determined from the ratio of minimum/maximum counts. Images of an American College of Nuclear Physicians cardiac single-photon emission computed tomographic phantom were acquired and the results were compared with those obtained from 194 centers in the United States. For cardiac studies with 201Tl and 99mTc, threshold values of 65% to 70% gave the best correlation (R2 > 0.94) between true and measured defect sizes, although the slope of the regression line was less than 0.95 for both isotopes. Small inferior defects demonstrated poor image contrast, particularly for 99mTc. Of the three defects in the American College of Nuclear Physicians phantom, the two largest were identified in the tomographic images. CONCLUSIONS: A multicrystal gamma camera system coupled with a rotating chair can be used for tomographic studies of the heart. Image quality is poorer than that seen on conventional single-photon emission computed tomographic systems, particularly for 99mTc.

Feasibility Studies↗
PubMedDate not supplied

Field strength in neuro-MR imaging: a comparison of 0.5 T and 1.5 T.

A study was undertaken comparing neurological magnetic resonance imaging at high (1.5 T) and mid (0.5 T) field strengths. Twenty-eight patients (20 head and 8 spine) from our routine case load volunteered to undergo two consecutive and identical MR studies on the two systems. The two MR systems were built by the same manufacturer and were equipped with essentially identical hardware and software. Individual patient studies were performed consecutively in adjacent MR suites, and pulse sequence parameters were replicated exactly at the two field strengths. One exception to this rule was that the second echo of the long TR sequence in the head was acquired with a narrow receiver bandwidth on the 0.5 T system. The resulting axial double echo long repetition time (TR) and sagittal short TR head images and sagittal short and double echo long TR spine images were graded by two blinded observers (senior staff neuroradiologists) on two levels. First, the images were graded for image quality, i.e., conspicuousness of artifacts and clarity in depiction of normal and pathologic anatomy. Second, diagnostic accuracy of MR was assessed relative to the clinical-pathologic diagnosis in each case. The image quality of the 1.5 T system was rated superior in both the head and spine for most specific items assessed. This observer preference for 1.5 T images did not, however, translate into greater diagnostic accuracy for the 1.5 T system in the head. Although the 1.5 T system did have a slight advantage in diagnostic accuracy in the spine, a significant difference was not found.

Brain↗
PubMedDate not supplied

CT reconstruction algorithm selection in the evaluation of solitary pulmonary nodules.

OBJECTIVE: We have observed a significant CT artifact in the evaluation of lung nodules that occurred with the use of high-spatial-frequency reconstruction algorithms. We have seen this lead to a false-positive diagnosis of calcification in a small uncalcified lung nodule. Because of the seriousness of misinterpretation of benign calcification in an uncalcified nodule, we reviewed the various effects of several reconstruction algorithms on different scanners. MATERIALS AND METHODS: Using high-spatial-frequency, smoothing, and intermediate reconstruction algorithms, we studied standardized cylinders in a CT reference phantom and lung nodules in eight patients. Algorithms on four CT scanners were analyzed. RESULTS: We found peripheral edge enhancement artifact on some CT images of phantom cylinders and uncalcified lung nodules. The images with edge enhancement artifact were obtained from two scanners with the use of high-spatial-frequency algorithms (Picker 1200 SX and GE HiSpeed Advantage). CONCLUSION: Use of high-spatial-frequency reconstruction algorithms for the analysis of lung nodules with thin-section CT may lead to an erroneous diagnosis of calcification.

Algorithms↗
PubMedDate not supplied

Monte Carlo advice.

The generation of long, high quality random number sequences for Monte Carlo simulations using minicomputers is considered. The importance of the thorough testing of Monte Carlo random number generators is emphasized. A recommendation is given to authors of Monte Carlo papers to specify their random number generator and to describe the randomness testing which that generator has undergone.

Computers↗
PubMedDate not supplied

Dose calibrator response to brachytherapy sources: A Monte Carlo and analytic evaluation.

It is well known that the dose calibrator response/unit exposure rate depends significantly upon source energy. However, investigation of 137Cs, 192Ir, and 226Ra brachytherapy sources by empirical, analytical, and Monte Carlo techniques shows that source filtration significantly affects the calibrator reading to exposure rate conversion factor. The results demonstrate that for each clinically used filtration thickness an exposure calibrated standard source is required to establish the response of the well chamber. An interesting consequence of this analysis is that the Sievert point dose algorithm for clinical sources overestimates the dose on the order of 3% at distances of approximately 3.5 cm from the source.

Brachytherapy↗
PubMedDate not supplied

Routine quality control tests for film-screen mammographic systems with automatic exposure control.

Quality control of the contrast and density of mammograms is of extreme importance not only because of patient dose considerations but also because of the need to monitor changes in the breast over extended periods of time. A phantom and test technique has been developed and used at two institutions for monitoring the ability of mammographic generators and phototiming systems to provide consistent contrast and density. The phantom consists of a solid acrylic block and an embedded aluminum step wedge designed specially for low kVp use. Optical densities of various portions of the phantom are used to determine constancy of density and contrast. By minimizing fluctuations due to processing and film handling, normal variations were reduced enough to determine changes in contrast and density due to generator and phototimer changes equivalent to those monitored in processor quality control programs. The data have been correlated with changes in processor function. Changes in density and contrast values have also been related to phototimer malfunction and reduced image quality.

Autoanalysis↗
PubMedDate not supplied

Performance testing of a dedicated magnetic resonance peripheral blood flow scanner.

This work presents a novel investigation of an NMR device to measure blood flow. Continuous-wave magnetic resonance scanners are now available for noninvasive peripheral blood flow measurements. The appearance of dedicated peripheral blood flow scanners in the clinical setting requires analysis of system performance. No reports were found that explore methods or results of clinical MR blood flow scanner performance evaluation. This work was undertaken to identify the testing procedures and characteristics of a clinical, dedicated NMR blood flow scanner. The dependence of flow measurement on tubing size, material, offset from isocenter, and angulation was examined. In addition, the precision and accuracy of the scanner were investigated. The results demonstrate a strong dependence between the measured blood flow and both the tube size and flow rate. The tube offset results exhibited a region of weak dependence in the center of the bore, which becomes stronger near the edge. The measured flow rate was found to be relatively insensitive to tube angles less than 30 degrees to 55 degrees. The repeatability was typically better than 5% and the table positioning was found to be highly accurate.

Humans↗
PubMedDate not supplied

Serial myocardial T2 relaxation time measurements in normal subjects and heart transplant recipients.

Myocardial proton T2 relaxation measurements were performed on five normal subjects over 4 weeks (20 measurements) and on nine heart transplant recipients (35 measurements). All magnetic resonance measurements were performed with a 1 T system. All patients had endomyocardial biopsy the same day as magnetic resonance imaging. Results of biopsies were normal on 32 occasions and abnormal three times (two cases of acute rejection and one case of myocardial edema). T2 values for normal subjects were 46.6 +/- 8.1 and 46.9 +/- 4.9 msec (septum and left ventricular free wall, respectively). T2 values for transplant recipients with normal results of biopsies were 44.5 +/- 7.8 and 43.1 +/- 7.5 msec. T2 values in three patients with abnormal results from biopsies were elevated (69 +/- 7.6 msec, range 59.7 to 77.6 msec). The results show similar values in normal subjects and transplant recipients with normal results from biopsies. Increased T2 values in three patients with abnormal results from biopsies indicate that relaxation time measurements may be of value to identify patients at risk of rejection.

Adolescent↗