Muscle necrosis in the extremities: evaluation with Tc-99m pyrophosphate scanning--a retrospective review

A retrospective review was done of 34 extremities studied between 1981 and 1985 with technetium-99m pyrophosphate scanning; 22 were subsequently amputated. Results of detailed pathologic examination or immediate postoperative examination of the resected extremity were available in 16 cases. In these cases, scanning had allowed correct prediction of the level of amputation and of the specific areas of muscle infarction in 13 cases. In the one case in which amputation was performed for infection rather than muscle necrosis, the lack of necrosis was correctly predicted with the scan. The limited results of this study indicate that the Tc-99m pyrophosphate scan allows the location of necrotic muscle to be predicted accurately and may therefore be a useful adjunct in determining the best level for ultimate amputation. Special caution is required in those cases in which muscle necrosis is due to acute causes (e.g., traumatic thrombosis) rather than chronic vascular disease.     

Pulse sequence optimization for MR imaging using a paramagnetic hepatobiliary contrast agent

Paramagnetic agents enhance contrast between tissues in magnetic resonance (MR) imaging by altering tissue relaxation times. The effect of these changes on MR image intensity depends in part on the choice of operator-controlled pulse sequence parameters. With the newly described paramagnetic hepatobiliary contrast agent, iron(III) ethylenebis-(2-hydroxyphenylglycine), Fe(EHPG)-, an in vivo experimental analysis of pulse sequence optimization was performed on the rat. We compared the enhancement of the liver divided by background noise, EL/N, of standard inversion-recovery (IR) and spin-echo (SE) T1-weighted pulse sequences and several pulse sequences theoretically predicted to have improved EL/N. Optimization of the echo time (TE = TEmin) gave a substantial (greater than 60%) increase in EL/N over the standard IR and SE pulse sequences. Images obtained with optimized repetition rate and inversion time gave only a slight additional improvement. Within the uncertainties of our relaxation measurements, the measured changes in EL/N with pulse sequence optimization corresponded well with theoretical predictions. With the experimental and theoretical data, the importance of using a short echo time to obtain maximal T1 contrast in contrast-enhanced MR imaging and the relative merits of optimized SE versus IR pulse sequences for contrast-enhanced MR imaging are discussed.     

Multiphasic MR imaging: a new method for direct imaging of pulsatile CSF flow

A new technique is described that allows for the creation of pure pulsatile flow magnetic resonance (MR) images in a single acquisition. Five to 16 electrocardiographically gated images spanning the entire cardiac cycle are obtained with use of a gradient-echo pulse sequence. The section can be varied from 4 mm thick to full thickness projection. Taken singly, each image provides direct assessment of flow direction and velocity. Subtraction of image pairs eliminates signal detected from stationary protons, producing images of pulsatile flow. In this study the technique was used to image the flow of cerebrospinal fluid (CSF) in healthy subjects and in one patient with syringohydromyelia. The data suggest that multiphasic MR imaging provides a powerful means for the noninvasive assessment of CSF pulsatile flow dynamics and may have potential clinical application for the investigation of a variety of abnormalities such as normal pressure hydrocephalus, syrinx, and spinal block.     

Rickettsia rickettsii infection of cultured human endothelial cells induces tissue factor expression

Microvascular thrombi underlie many of the clinical manifestations of Rocky Mountain spotted fever (RMSF), a disease characterized by Rickettsia rickettsii infection of vascular endothelial cells. Studies were designed to determine whether R rickettsii-infection of cultured human umbilical vein endothelial cells results in tissue factor (TF) induction, a process that could directly activate coagulation in infected vessels. Whereas uninfected endothelial cell cultures showed essentially undetectable TF mRNA and activity, both TF mRNA and activity were present after R rickettsii infection. TF mRNA levels were transient, peaking at 4 hours after the initiation of infection, whereas the peak of TF activity occurred at 8 hours. Induction of the TF response requires the intracellular presence of R rickettsii organisms, because uninfected rickettsia were ineffective and the response was blocked by inhibiting rickettsial entry using cytochalasin B. TF induction was not mediated by endothelial cell release of soluble factor, because no response was induced using culture medium conditioned by R rickettsii-infected cells. Furthermore, preadsorption of suspensions of R rickettsii with polymyxin B to remove contaminating lipopolysaccharide did not eliminate the TF response. Induction of TF in vital endothelial cells during R rickettsii infection could be the trigger for vascular thrombus formation of RMSF.     

MR gated subtraction angiography: evaluation of lower extremities

We report the first clinical experience with a new method for projective imaging of blood vessels (angiography) using magnetic resonance. Vascular contrast is produced noninvasively by the phase response of moving protons. Diastolic and systolic gated images produce, respectively, flow signal and flow void; the difference image is a map of the pulsatile flow: an arteriogram. Preliminary studies are presented of the lower extremities of one healthy volunteer and four patients (one each with occlusive disease, soft-tissue tumor, arteriovenous malformation, and venous femoral-popliteal graft). Patient data are compared with accompanying conventional arteriograms, and the new method is discussed.     

Indications for breast imaging in women under age 35 years

To determine appropriate indications for breast imaging in young women, the authors correlated patient histories with mammographic and/or sonographic findings and biopsy or follow-up results for 625 patients aged 13-34 years. The only important indications were a palpable mass and suspicion of an abscess. Of the 335 studies performed for evaluation of a palpable mass, 184 (55%) were normal, 28 (8%) were compatible with benign disease, and 123 (37%) were suggestive of malignancy. Biopsies were performed in 73 patients; the findings were benign in 67 cases, and carcinoma was found in six. Imaging studies were considered helpful in four of the 15 cases of suspected abscess, in that the studies established the presence and extent of an abscess. Studies in 275 women were performed for a variety of other indications. The findings were normal in 239 (87%) studies, benign in 21 (8%), and suggestive of malignancy in 15 (5%); there were no known carcinomas in any of the patients. Women with the "low-yield" indications identified in this study should be followed up clinically rather than referred for imaging studies.     

Irradiation induces release of von Willebrand protein from endothelial cells in culture

Human umbilical vein endothelial cells in tissue culture were irradiated with doses between 0 and 40 Gy, and the released von Willebrand (vW) protein and that which remained associated with the cells was quantitated. Doses of 20 Gy and higher produced a statistically significant increase in amount of vW protein secreted. This release was present whether the cells were labeled continuously throughout the experiment or just prelabeled before irradiation. An increase in fibronectin secretion was not observed. The release response to radiation was slow, reaching significance close to 24 hours after irradiation. The release of vW protein was not due to cell lysis, because the secreted vW protein contained very little of the large 260- kilodalton vW precursor subunit present in cell lysates and the cells appeared intact by immunofluorescence staining.