The Osteoarthritis Initiative (OAI) magnetic resonance imaging quality assurance update.

OBJECTIVE: Longitudinal quantitative evaluation of cartilage disease requires reproducible measurements over time. We report 8 years of quality assurance (QA) metrics for quantitative magnetic resonance (MR) knee analyses from the Osteoarthritis Initiative (OAI) and show the impact of MR system, phantom, and acquisition protocol changes. METHOD: Key 3T MR QA metrics, including signal-to-noise, signal uniformity, T2 relaxation times, and geometric distortion, were quantified monthly on two different phantoms using an automated program. RESULTS: Over 8 years, phantom measurements showed root-mean-square coefficient-of-variation reproducibility of <0.25% (190.0 mm diameter) and <0.20% (148.0 mm length), resulting in spherical volume reproducibility of <0.35%. T2 relaxation time reproducibility varied from 1.5% to 5.3%; seasonal fluctuations were observed at two sites. All other QA goals were met except: slice thicknesses were consistently larger than nominal on turbo spin echo images; knee coil signal uniformity and signal level varied significantly over time. CONCLUSIONS: The longitudinal variations for a spherical volume should have minimal impact on the accuracy and reproducibility of cartilage volume and thickness measurements as they are an order of magnitude smaller than reported for either unpaired or paired (repositioning and reanalysis) precision errors. This stability should enable direct comparison of baseline and follow-up images. Cross-comparison of the geometric results from all four OAI sites reveal that the MR systems do not statistically differ and enable results to be pooled. MR QA results identified similar technical issues as previously published. Geometric accuracy stability should have the greatest impact on quantitative analysis of longitudinal change in cartilage volume and thickness precision.

The osteoarthritis initiative (OAI) magnetic resonance imaging quality assurance methods and results.

OBJECTIVE: To outline the osteoarthritis initiative's (OAI) magnetic resonance (MR) system quality assurance (QA) processes and present the first 3 years' results. METHOD: OAI MR QA included acquisitions evaluated manually at each of the four sites and other acquisitions assessed by an automated computer program. Key image characteristics such as signal-to-noise, contrast-to-noise, signal uniformity, T2 relaxation times, local and global geometric distortion were quantified monthly using the automated program. RESULTS: Uniformly high quality, artifact-free subject images were obtained from all four OAI 3 tesla MR facilities. Over a 3-year period, key criteria for quantitative cartilage morphometry were excellent with a 190.0 mm diameter and 148.0 mm length object having reproducible diameter (0.04% RMS CV) and length (0.56% RMS CV). This resulted in spherical volume reproducibility of 0.46% RMS CV. Ghost levels were consistently <0.2%. T2 relaxation time varied longitudinally site-by-site from 2.3 to 18.8% RMS CV. All other measures of MR system stability were met except: 3.0 mm and 5.0 mm slice thicknesses were consistently larger than expected; knee coil signal uniformity and signal level varied significantly over time. CONCLUSIONS: OAI MR QA results compared favorably to prior publications and identified similar technical issues for geometric measurements. The longitudinal variations measured in the OAI QA process should have minimal impact on the accuracy and reproducibility of cartilage thickness and volume quantification. This stability should enable direct comparison of baseline and follow-up images. Cross-comparison of the results from all four OAI sites reveals that the MR systems are sufficiently uniform to enable results to be combined.

Effects of IFN-beta on human cerebral blood flow distribution.

The effect of interferon-beta1b (IFN-beta) on human cerebral blood flow distribution was examined in five multiple sclerosis patients using functional brain single-photon emission tomography (SPECT). Of nine regions of interest studied, only the basal ganglia exhibited a significant change (increase) in relative photon emission intensity (i.e., relative blood flow) when comparing SPECT scans obtained 6 h after s.c. IFN-beta injection with scans obtained at the same time of day (noon) 30 h after IFN-beta injection (IFN-beta-free day). The increase in relative blood flow to the basal ganglia following IFN-beta injection correlated positively with changes in mean arterial pressure (MAP). Additional studies will be required to determine the relevance of these observations for IFN-beta-induced central nervous system side effects.

Effects of strength training and detraining on muscle quality: age and gender comparisons.

Maximal force production per unit of muscle mass (muscle quality, or MQ) has been used to describe the relative contribution of non-muscle-mass components to the changes in strength with age and strength training (ST). To compare the influence of age and gender on MQ response to ST and detraining, 11 young men (20-30 years), nine young women (20-30 years), 11 older men (65-75 years), and 11 older women (65-75 years), were assessed for quadriceps MQ at baseline, after 9 weeks of ST, and after 31 weeks of detraining. MQ was calculated by dividing quadriceps one repetition maximum (IRM) strength by quadriceps muscle volume determined by magnetic resonance imaging. All groups demonstrated significant increases in IRM strength and muscle volume after training (all p < .05). All groups also increased their MQ with training (all p < .01), but the gain in MQ was significantly greater in young women than in the other three groups (p < .05). After 31 weeks of detraining, MQ values remained significantly elevated above baseline levels in all groups (p < .05), except the older women. These results indicate that factors other than muscle mass contribute to strength gains with ST in young and older men and women, but those other factors may account for a higher portion of the strength gains in young women. These factors continue to maintain strength levels above baseline for up to 31 weeks after cessation of training in young men and women, and in older men.

MRI videotape series 8850

Minnetonka, Minn: EduMed, 1999. Videotape, $95.00 for each tape.

Coronary MRA: use in assessing anomalies of coronary artery origin.

PURPOSE: The purpose of this work was to describe the use of coronary MR angiography (MRA) in the clinical evaluation of a series of patients with anomalous origin of the coronary arteries suspected on coronary angiography. METHOD: Eight patients underwent coronary MRA to further define variant coronary anatomy that was found on coronary angiography. A 2D segmented k-space gradient echo sequence was used with breath-holding. MRA images were assessed for traversal of an anomalous artery between the aorta and pulmonary artery trunks, which carries the greatest clinical significance. RESULTS: Of six patients with anomalous origin of the right coronary artery on angiography, two were shown by MRA to have an interarterial course of the anomalous vessel. Neither of two left coronary arteries with ectopic origin coursed between the great arteries, although one passed through the septum. CONCLUSION: Coronary MRA is a useful adjunctive technique to angiography in the evaluation of the relationship of anomalous coronary arteries to the great arteries.

Anomalies of pulmonary veins: usefulness of spin-echo and gradient-echo MR images.

OBJECTIVE: We compared the value of spin-echo and gradient-echo MR images in the evaluation of anomalies of pulmonary veins. MATERIALS AND METHODS: Fourteen patients with a variety of developmental anomalies of pulmonary veins underwent MR imaging examination. Axial T1-weighted spin-echo and gradient-echo MR images were evaluated retrospectively on separate occasions during which visualization of normal and anomalous pulmonary veins was determined. RESULTS: Of 52 pulmonary veins, 46 (88%) were identified on T1-weighted spin-echo images and 50 (96%) on gradient-echo images. Two patients had atresia of both left pulmonary veins. Of 14 anomalous veins, 11 (79%) were revealed on spin-echo images and 13 (93%) on gradient-echo images. CONCLUSION: Both spin-echo and gradient-echo MR images were accurate in revealing anomalies of pulmonary veins. In our study, gradient-echo images were equal or superior to spin-echo images.

Modeling the motion of the internal tongue from tagged cine-MRI images.

A new technique, tagged Cine-Magnetic Resonance Imaging (tMRI), was used to develop a mechanical model that represented local, homogeneous, internal tongue deformation during speech. The goal was to infer muscle activity within the tongue from tissue deformations seen on tMRI. Measurements were made in three sagittal slices (left, middle, right) during production of the syllable /ka/. Each slice was superimposed with a grid of tag lines, and the approximately 40 tag line intersections were tracked at 7 time-phases during the syllable. A local model, similar to a finite element analysis, represented planar stretch and shear between the consonant and vowel at 110 probed locations within the tongue. Principal strains were calculated at these locations and revealed internal compression and extension patterns from which inferences could be drawn about the activities of the Verticalis, Hyoglossus, and Superior Longitudinal muscles, among others.

Measurement of absolute epicardial coronary artery flow and flow reserve with breath-hold cine phase-contrast magnetic resonance imaging.

BACKGROUND: Noninvasive measurement of absolute coronary arterial flow and coronary flow reserve would be of considerable use in the diagnosis and management of patients with coronary artery disease. Phase-contrast magnetic resonance imaging (MRI) has been used to measure flow in a variety of vessels. The goal of the present study was to determine if MRI measurements of coronary artery flow in a single breath-hold can be used to determine flow reserve and the severity of pericardial stenosis. METHODS AND RESULTS: In eight mongrel dogs, a closed chest model of partial left anterior descending coronary artery (LAD) occlusion was created. Coronary flows in the left circumflex artery (LCx) and LAD were measured at rest and during adenosine infusion using velocity-encoded, breath-hold MRI and perivascular ultrasound (US) flowmeters. MRI measurements of absolute coronary flow and coronary flow reserve were highly correlated with US (r = .96 and .94, respectively). Flow reserve measured in the constricted LAD was significantly lower than that in the unconstricted LCx by both US (P = .002) and MRI (P = .011). CONCLUSIONS: MRI measurements of coronary flow and flow reserve were in good agreement with US measurements. In addition, MRI measurements of coronary flow reserve successfully discriminated stenotic from normal vessels. These results indicate that MRI is a useful method for the noninvasive assessment of coronary flow and stenosis.

Quality assurance for abdominal CT: a rapid, computer-assisted technique.

OBJECTIVE: Maintaining high standards in a large CT imaging department with multiple scanners, a large technical and clerical staff, and a rotating staff of radiologists is an ongoing challenge. We undertook a project to design and implement a simple, rapidly performed computer-assisted system of quality assurance (QA) for use in abdominal CT. In our project, we also analyzed the results of that QA system. MATERIALS AND METHODS: We graded 1810 abdominal CT studies done in a 50-week period, using a three-point scale to indicate the quality of the following five parameters of technical quality: IV contrast enhancement, oral contrast opacification, window settings and artifacts, conformity to radiologists' protocol, and completeness and accuracy of header and scout data. In addition, a parameter reflecting performance of the film library and clerical staff was similarly graded. To provide a measure of peer review for radiologists, any disagreements with prior CT study reports were recorded when comparison studies were reviewed in the process of CT interpretation. A commercially available spreadsheet and database software program was tailored to allow rapid, easily performed data entry and analysis. Tables and graphs showing performance of technologists and film library and clerical staff were generated. This customized program was made available on the radiology department computer network. Results generated by the program were further analyzed with linear regression models. RESULTS: Our QA system was successfully integrated into the routine operation of the abdominal CT division. During the first 11.5 months of operation, the system reflected improvement in each of the technical parameters with a statistically significant improvement in the combined average technical score (from 1.15 to 1.68 on a scale of 0-2; p < .0001). The "Throughout Speed/Old Exams" parameter for performance of the film library and clerical staff, which was analyzed separately from the technical parameters, also improved significantly (from 1.3 to 1.8; p < .02). Improvements were statistically significant, even when we controlled for potential variations in quality among different CT scanners and variations among the radiologists who rated the quality of the examination. Thirty-eight disagreements with previous scan interpretations (5% of all scan comparisons) were recorded for evaluation at peer review conferences. CONCLUSION: The ability to monitor performance continuously using a rapid, computer-assisted system has effected measurable improvement in our CT service. Technologist and film library and clerical staff performance improved for all parameters studied. Deficiencies were revealed and trends demonstrated. The QA system allowed us to identify disagreements in interpretation of CT examinations for subsequent peer review by radiologists. Our QA software program has been made available on the Internet as freeware to licensed Excel users via anonymous file transfer protocol at Internet Protocol 134.192.6.110.