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R L Morin

Publications and source records attributed to R L Morin.

At least 19 recordsLinked to original sources
PubMed1992

Solitary pulmonary nodule: CT evaluation of enhancement with iodinated contrast material--a preliminary report.

The authors hypothesized that the degree of contrast material enhancement of a pulmonary nodule, measured with computed tomography (CT), may indicate the likelihood of malignancy. Fifty-two patients with uncalcified solitary pulmonary nodules (diameter, 6-30 mm) were studied. Five single serial thin-section CT scans were obtained at 1-minute intervals after injection of 100 mL of nonionic contrast material. Twenty-two patients were excluded because the diagnosis was not clearly established: The observation period was less than 2 years, or the examination was technically inadequate. Malignant nodules were identified in 23 of the 30 remaining patients, and benign nodules were identified in seven. Within the first 2 minutes after the injection, all the malignant nodules had enhanced by 20 HU or greater (only one benign nodule had that degree of enhancement). The authors conclude that the degree of contrast material enhancement of pulmonary nodules as measured with CT may indicate the likelihood of malignancy.

Adult↗
PubMed1992

Effect of titanium endoprostheses on bone mineral density measurements, using quantitative computed tomography.

Quantitative computed tomography has been used extensively to measure bone mineral density; particularly in the vertebral column and in the proximal portion of the femur in human beings with osteoporosis. Other potential applications of this technique include evaluation of bone adjacent to metallic endoprostheses and evaluation of fractures as they heal. Unfortunately, metal causes severe image degradation, principally seen as starburst streaking. One method used to decrease these artifacts is by imaging less-attenuating materials, such as titanium alloy. Titanium decreases image degradation sufficiently to allow accurate determination of the geometric properties of cadaveric bone. In our study, the effect of a titanium segmental endoprosthesis on bone mineral density measurement was determined by use of bone specimens from dogs and calibration standards. Titanium decreased the bone mineral density of calibration solutions from 6.8 (500 mg/cm3) to 17.7% (250 mg/cm3), and increased bone mineral density of cortical bone by 5.3%. Titanium did not affect the repeatability of these scans, indicating that the error caused by titanium was systematic and can be corrected. Our data were suggestive that quantitative computed tomography can be used to measure bone mineral density of cortical bone adjacent to titanium endoprostheses, with a predictable increase in density measurement.

Animals↗
PubMed1991

Quantitative CT for the evaluation of bone healing.

Quantitative computed tomography (QCT) was used to quantitate the structural strength and local material properties of healing tibial osteotomies in 32 dogs. Dogs were divided into four equal groups, euthanatized at either 2, 4, 8, or 12 weeks and imaged with QCT. Invasive techniques were used to determine (1) the torsional properties of the bone; (2) the local stiffness properties and calcium content within the bone; and (3) histologically determined new bone formation and porosity. QCT was strongly associated with the maximum torque (R2 = 0.44) and torsional stiffness (R2 = 0.69) of the healing bone. QCT had strong correlations with the local stiffness (R2 = 0.64), calcium content (R2 = 0.61), new bone (R2 = 0.84), and porosity (R2 = 0.84) of healing tissues.

Animals↗
PubMed1991

The determination of bone fracture properties by dual-energy X-ray absorptiometry and single-photon absorptiometry: a comparative study.

Dual-energy X-ray absorptiometry (DEXA) and single-photon absorptiometry (SPA) were used to quantitate the structural strength and local material properties of healing tibial osteotomies in 32 dogs. Dogs were divided into four equal groups, euthanatized at either 2, 4, 8, or 12 weeks, and imaged with DEXA and SPA. Invasive techniques were used to determine (1) the torsional properties of the bone, (2) the local stiffness properties and calcium content within the bone, and (3) new bone formation and porosity by histology. There were no differences between SPA and DEXA in their associations with the torsional properties of bone. SPA and DEXA had strong correlations with the ultimate torque (R2 = 0.76, 0.51) and the torsional stiffness (R2 = 0.68, 0.53) of bone. SPA and DEXA of periosteal callus, endosteal callus, and cortical bone had similar associations with indentation stiffness, calcium content, new bone formation, and porosity. SPA of gap tissue had significantly stronger associations with these four parameters than DEXA (P less than 0.05). Correlation coefficients (R2) with these local material properties ranged as high as 0.82 for SPA with new bone formation in the gap tissue and 0.73 for DEXA with indentation stiffness of periosteal callus.

Absorptiometry, Photon↗
PubMed1991

Hand dose measurements in interventional radiology.

Measurements of radiation dose to the hand were conducted using TLD ring badges for individual interventional radiology cases. Results from over 30 examinations (including transhepatic cholangiograms and biliary and nephrostomy procedures) conducted by four radiologists using identical equipment show an average hand dose of 1.5 mGy (150 mrad) per procedure. Hand dose varied inversely with distance from the patient. Due to variable hand positions during clinical examinations, fluoroscopic time was not found to be a good indicator of hand dose.

Fluoroscopy↗
PubMed1991

Technical exhibits.

Explore the source record for details and available documents.

Exhibitions as Topic↗
PubMed1991

CT evaluation of solitary pulmonary nodules: value of 185-H reference phantom.

The pulmonary nodule CT reference phantom is widely used in the evaluation of nodules 2 cm or less in diameter. It is used to detect benign patterns of calcification that are not visible on thin-section CT scans. Since 1986, the reference nodules have been manufactured with a nominal composition of 185 H. The multicenter study published in 1986 used nodules with a nominal composition of 264 H, 100 H more than the threshold value reported by Siegelman et al. in 1980. In the multicenter study, one of 37 nodules diagnosed as benign with the phantom proved to be malignant. The purpose of this study was to determine the misdiagnosis rate with the 185-H phantom and to ascertain whether the malignant tumors predicted to be benign actually contained calcification. We retrospectively reviewed 296 cases in which examinations had been performed with the 185-H nodules since 1986. Eighty-five nodules were diagnosed as benign by comparison to the reference phantom. These 85 contained no visible calcification on thin-section CT scans. Ten of the 85 cases were shown to be malignant tumors. Eight were diagnosed as having a high probability of benignity. Two were diagnosed as having a moderate probability of benignity. Calcium was present in the tissue of all six nodules available for review. Fifty-nine of the 85 nodules were still clinically indeterminate at the time of this review. Even if all of the clinically indeterminate nodules are benign, the misdiagnosis rate would be significantly higher than in most previous studies. Although analysis by using the reference phantom with 185-H nodules may indicate a high probability of benignity, close radiologic follow-up is necessary.

Adult↗
PubMed1991

Multiplanar quantitative computed tomography for bone mineral analysis in dogs.

The purpose of this study was to determine the precision and accuracy of quantitative computed tomography bone mineral analysis in dogs in coronally reconstructed images. Nonhomogeneous tissues, such as bones with fractures or deformities, may be better analyzed if multiplanar reconstruction of the transaxial data could be performed without degradation of information. Our analysis demonstrated that coronal reconstruction of quantitative-computed tomography data was precise (1.2 to 4.7%) and accurate (1.3 to 7.5%) in vitro. The technique displays high-quality images, which can be analyzed at any location within the volume scanned. Quantitative computed tomography of canine osteotomy healing in vivo accurately determined bone mineral density of selected regions of interest. Bone mineral density correlated highly with calcium content of the tissue (R2 = 0.76, P less than 0.0001).

Animals↗
PubMed1990

Quantification of bone healing. Comparison of QCT, SPA, MRI, and DEXA in dog osteotomies.

Four noninvasive imaging modalities were used to quantitatively evaluate and compare tibial osteotomy healing in dogs. Quantitative computed tomography (QCT), magnetic resonance imaging (MRI), single-photon absorptiometry (SPA), and dual-energy x-ray absorptiometry (DEXA) were the four techniques examined. Bilateral tibial osteotomies were performed in 32 dogs divided into four groups. The osteotomies were stabilized with a 2-mm gap using unilateral external skeletal fixation. Dogs were anesthetized, imaged with the four noninvasive techniques, and killed at 2-12 weeks. Invasive techniques were used to determine: 1) the torsional properties of the bone; and 2) the local stiffness properties and calcium content within the bone. The techniques which had the strongest associations with the torsional properties of the osteotomies were QCT, SPA and DEXA. Generally, QCT and SPA had marginally stronger correlations than DEXA; but, overall, there were no differences between the techniques. MRI had the poorest associations with the torsional properties of the osteotomies. Generally, QCT had the strongest correlations with local material properties, such as indentation stiffness and calcium content. SPA had the second strongest correlations with calcium content and had the third strongest correlations with indentation stiffness behind DEXA. DEXA had the third strongest correlations for calcium content. With the exception of some of the correlations with indentation stiffness, MRI had the poorest associations with the local parameters studied.

Absorptiometry, Photon↗
PubMed1989

Magnetic resonance imaging phase encoding: a pictorial essay.

A set of MRI images with various degrees of phase encoding were generated from the same raw data set. The resultant pictorial teaching aid is useful in developing an intuitive understanding of the mechanics and principles of phase encoding in two dimensional, Fourier transform magnetic resonance imaging.

Humans↗
PubMed1989

Purchasing medical imaging equipment.

This report presents a summary of the steps and factors involved in the purchasing of medical imaging equipment. Although the range of variations in this process is broad, some fundamental common factors are useful to consider before initiating the acquisition process.

Capital Expenditures↗
PubMed1988

Comparison of dual-energy x-ray absorptiometry and dual photon absorptiometry for bone mineral measurements of the lumbar spine.

A new x-ray-based (dual-energy x-ray absorptiometry [DEXA]) instrument for measurement of bone mineral in the spine and hips (QDR-1000, Hologic, Inc.) was compared with a commercial dual photon absorptiometry (DPA) instrument that uses a 153Gd source (DP3, Lunar Radiation Corporation). Measurements were made on phantoms and lumbar spines of patients to study accuracy, precision, limitations, and compatibility of results between instruments. Both instruments measure bone mineral of integral bone in terms of area bone density with an entrance exposure of less than 5 mR. For spinal bone mineral measurements, the DEXA instrument had a shorter scanning time and higher resolution images than the DPA system. The DEXA instrument also showed better precision in a spine phantom and reduced influence of thickness for patient measurement. For bone mineral content, accuracy was about equal for both instruments; for measurements of the area of the region of interest, accuracy was better with the DEXA instrument. With both instruments, fat had little effect on bone mineral density in bone phantom studies. Measurements on both instruments were influenced by the location of a bone phantom within the photon beam. Results in patients showed good correlation (r = 0.988) for bone mineral density. Measurements of bone mineral density in patients were consistently lower with the DEXA instrument because of better accuracy in area measurements. The new x-ray-based instrument is a major advance in bone mineral absorptiometry and provides improved, yet less expensive, measurements in research and clinical applications.

Adipose Tissue↗
PubMed1978

Electron dose reduction coefficients for seven radionuclides and cylindrical geometry.

In determining internal radiation absorbed dose it is frequently not possible to assume a uniform distribution of radionuclide in an infinite, homogeneous, absorbing material. When the source-target geometry is such that the target is source-free, special considerations must be given to the dose contributions from electrons, since the conventional assumption of 100% absorption of non-penetrating radiations leads to overestimation of the absorbed dose. The absorbed dose from electrons determined at a point within the source-free region depends upon the depth within it. Electron dose reduction coefficients determined at appropriate distances from the source surface are multiplied by the electron doses determined from the general absorbed dose equation. This method of correcting for source-free regions has been applied to cylindrical and planar geometry, for spinal cord and nerve root dosimetry in cisternography. Utilising published scaled point kernels for mono-energetic electrons, electron dose reduction coefficients have been determined as a function of depth from the source surface for cylindrical source-free regions of radii 0.5, 0.05 cm and infinity, and seven gamma-ray-emitting radionuclides: 51Cr, 67Ga, 99Tcm, 111In, 113Inm, 169Yb and 203Pb. These values may be used in other internal radiation absorbed dose situations, and similar techniques applied to other source-target geometries.

Humans↗
PubMed1975

Dosimetry of several DTPA radiopharmaceuticals in cisternography.

Previously published biologic distribution and clearance data for 169Yb-DTPA in cisternography were utilized to obtain effective spinal segment clearance data for six other easily dhelated radionuclides: 99mTc, 113mIn, 111In, 67Ga, 51Cr, and 203Pb. Absorbed radiation doses to the spinal cord and nerve roots were calculated for each radioactive DTPA compound, employing appropriate cylindrical geometry and reduction coeffients for the dose contributions from the electrons of each radionuclide. Doses are maximal at the surface and decrease rapidly with distance from the surface. The relative useful photon flux from each DTPA radiopharmaceutical for approximately the same average absorbed radiation dose to the spinal cord was determined. The results indicate that 111In and 203Pb should be considered as possible radionuclide tags for DTPA cisternographic imaging.

Brain Neoplasms↗
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

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

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↗