Blood flow distribution in necrotic versus nonnecrotic rabbit hearts.

The spatial myocardial blood flow heterogeneity of the normal heart was previously investigated by means of the standard microsphere-defined regional myocardial blood flow in nonischemic hearts. We determined the probability density functions of coronary blood flows in the rabbit heart at selected macroautoradiographic 20-microns cross-sections of the left ventricle in nonischemic as well as infarcted hearts. Macroautoradiography gave us spatial resolutions of 0.1-0.2 mm. As a tracer we used 14C-iodoantipyrine given into the root of the aorta. We report here for the first time a systematic study of the shape of the flow probability density functions during acute regional myocardial necrosis. As the hearts became progressively and extensively necrotic, the distribution of flows changed its characteristics showing two independent components. The first component was the peak representing the nonischemic regions in the hearts subjected to acute ischemia. The second component was a monotonically decreasing component associated with very low flows and necrosis in the severely hypoperfused portion of the hearts. This monotonically decreasing component became larger as the extent of ischemia increased and was well separated from the peak attributable to the nonischemic regions. We could not demonstrate a leftward shift of the nonischemic central peak in the ischemic hearts. Our research shows that in transaxial radionuclide cardiac sections, such as those that might be obtained and analyzed in clinical SPECT and clinical PET, variable amounts of myocardial necrosis will result in a composite curve of myocardial blood flow heterogeneities. One portion of the curve will indicate the distribution of flows in the nonischemic zones. The other portion will vary in magnitude with the extent of ischemia, exhibit the shape of monotonically decreasing curve. Depending upon the spatial resolution of the radionuclide imaging technique utilized, a border zone will exist representing the interface between normally perfused and occluded vascular beds. In our investigation, it was found that the border zone determined statistically was consistently and significantly smaller than the border zone determined visually.

Effect of field of view on MR diagnosis of rotator cuff tears.

PURPOSE: To determine the effect of decreasing the field of view (FOV) on the accuracy of MR for diagnosing rotator cuff tears. MATERIAL AND METHODS: One hundred shoulder MR scans with surgical correlation were evaluated for the presence or absence of a cuff tear. The sensitivity and specificity of MR relative to the surgical results were determined for the 59 patients scanned with a 24-cm FOV, and the 41 patients scanned with an 18-cm FOV. All other imaging parameters including acquisition time were identical. The sensitivity and specificity of the two groups were compared using a t-test. RESULTS: The specificity of MR for diagnosing a rotator cuff tear improved from 0.65 for the 24-cm FOV group to 0.89 for the 18-cm FOV group (P = 0.04). The sensitivity changed from 0.91 to 0.96 (P = 0.25). CONCLUSION: Reducing the FOV from 24 cm to 18 cm results in a statistically significant improvement in specificity of MR for diagnosing rotator cuff tears.

Diagnosis of partial and complete rotator cuff tears using combined gradient echo and spin echo imaging.

Most magnetic resonance (MR) studies evaluating the rotator cuff for tears have used T2-weighted imaging in the coronal oblique and sagittal oblique planes. T2*-weighted gradient echo imaging, however, has advantages over spin echo imaging, including contiguous slices without cross-talk, high contrast around the cuff, and intrinsically shorter imaging times which can be used to increase the number of signals averaged and thus improve the signal-to-noise ratio. We reviewed the shoulder MR scans of 87 consecutive patients who underwent both a MR scan and a shoulder arthroscopy during which the size of tears, if present, was graded. The reviewers were blinded as to the history and arthroscopic results. The MR scans included oblique coronal T2*-weighted gradient echo and oblique sagittal T2-weighted spin echo images. MR cuff grades were correlated with arthroscopic findings. For complete tears, the sensitivity of MR was 0.91 and the specificity 0.95. For partial tears, the sensitivity was 0.74 and the specificity 0.87. This accuracy is similar to two-plane T2-weighted imaging as previously reported in the literature. There was a statistically significant correlation (p < 0.0005) between the cuff grade as determined by MR and the arthroscopic findings.

MR diagnosis of meniscal tears of the knee: importance of high signal in the meniscus that extends to the surface.

OBJECTIVE: The presence of intrameniscal signal in contact with the surface is a commonly used criterion for the diagnosis of meniscal tear. This signal presumably represents the actual tear in the meniscus. However, some menisci with signal that contacts the surface are noted to be intact at arthroscopy whereas other menisci that have no signal in contact with the surface are found to be torn. We investigated the relationship between the presence of a meniscal tear at arthroscopy and the location within the menisci of signal that contacted the surface. We hypothesized that patterns were present that would improve the accuracy of MR diagnosis of a meniscal tear. MATERIALS AND METHODS: We reviewed the MR and arthroscopic findings from 200 consecutive patients who had both knee MR examinations and knee arthroscopy. There were 108 medial and 58 lateral meniscal tears on arthroscopy. Each MR examination was reviewed for three aspects of intrameniscal signal: the number of images showing signal possibly or definitely contacting the surface, the specific surfaces involved, and the signal location. The coronal and sagittal images were evaluated separately. We correlated each of these features with the presence of a meniscal tear at arthroscopy. RESULTS: Menisci with signal possibly contacting the surface had the same frequency of tears (three tears in 33 menisci) as menisci without signal contacting the surface (15 tears in 194 menisci). More than 90% of menisci with signal contacting the surface on more than one image were torn, but only 55% of medial and 30% of lateral menisci with such signal on only one image were torn. In the torn menisci with signal contacting the surface, such signal was seen only on sagittal MR images in 31% of the medial menisci and 45% of the lateral menisci. Sixteen percent of the torn lateral menisci had signal contacting the meniscal surface in only the anterior two thirds of the meniscus, whereas this was true in only 2% of the torn medial menisci. Distinct patterns were not seen in the association between tears and signal contacting either the superior or the inferior surface. CONCLUSION: We found definite patterns in the location of intrameniscal signal that comes in contact with the meniscal surface. These patterns vary in the frequency of associated meniscal tears. Although menisci with internal signal in contact with the surface are usually torn, a tear is less likely if such signal is present on only one image. Tears may be identifiable on only one image plane. Tears in the anterior horn of the lateral meniscus are not uncommon. Knowledge of these patterns should help in the MR diagnosis of meniscal tears.