Background-One of the features of high-risk atherosclerotic plaques is a preponderance of macrophages. Experimental studies with hyperlipidemic rabbits have shown that ultrasmall superparamagnetic particles of iron oxide (USPIOs) accumulate in plaques with a high macrophage content and that this induces magnetic resonance (MR) signal changes. The purpose of our study was to investigate whether USPIO-enhanced MRI can also be used for in vivo detection of macrophages in human plaques. Methods and Results-MRI was performed on 11 symptomatic patients scheduled for carotid endarterectomy before and 24 (nϭ11) and 72 (nϭ5) hours after administration of USPIOs (Sinerem) at a dose of 2.6 mg Fe/kg. Histological and electron microscopical analyses of the plaques showed USPIOs primarily in macrophages within the plaques in 10 of 11 patients. Histological analysis showed USPIOs in 27 of 36 (75%) of the ruptured and rupture-prone lesions and 1 of 14 (7%) of the stable lesions. Of the patients with USPIO uptake, signal changes in the post-USPIO MRI were observed by 2 observers in the vessel wall in 67 of 123 (54%) and 19 of 55 (35%) quadrants of the T2*-weighted MR images acquired after 24 and 72 hours, respectively. For those quadrants with changes, there was a significant signal decrease of 24% (95% CI, 33% to 15%) in regions of interest in the images acquired after 24 hours, whereas no significant signal change was found after 72 hours. Conclusions-Accumulation

We evaluated a method of semiautomated analysis of dynamic MR image series in renal transplants. Nine patients were studied twice, with an average time interval of 7 days. MR examination consisted of a run of 256 T1-weighted coronal scans (GE; TR/TE/flip: ‫؍‬ 11/3.4/60°; slice thickness ‫؍‬ 6 mm; temporal resolution ‫؍‬ 2 seconds). Gadolinium-DTPA (0.05 mmol/kg) was injected with an injector pump (5 ml/seconds). MR renographs of the cortex and medulla were obtained by segmentation of the renal transplant and placement of two regions of interest (ROIs) MR RENOGRAPHY (MRR) is a dynamic MR examination that provides functional information of the kidney and renal transplant in terms of changes in signal intensity of the renal parenchyma after gadolinium-DTPA injection (1-3). The high spatial resolution of the MR image allows cortical and medullary structures to be separated, a feature that is not possible with scintigraphic techniques and that may be of importance in separating disease processes affecting different parts of the kidney or renal transplant (1-12). Although biopsy is still the standard of reference for diagnosis of diseases affecting the kidney and renal transplant, early reports indicate the possible usefulness of MRR in discriminating disease processes such as acute rejection and acute tubular necrosis (8,10,11).The MR renograph is the time-dependent signal intensity of suitably placed regions of interest (ROIs) over cortical and medullary tissue (1-12). ROIs are usually hand-placed by the operator, who selects cortical and medullary tissue by visual inspection of the early-enhanced images on which contrast between cortical, medullary, and perinephric tissue is optimal.In cases in which contrast between cortex and medulla is suboptimal, however, ROI positioning may be more difficult and time consuming, thereby requiring skill and experience from the operator.In this work we present and evaluate a new method to derive cortical and medullary MR renographs of renal transplants by means of semiautomated ROI placement. The obtained renographs were tested nonparametrically on reproducibility. MATERIALS AND METHODS PatientsNine renal transplant recipients (three men and six women, 46 -66 years old, mean age 53.6 years) were included in this study. These patients were selected from a population of renal transplant recipients who took part in a larger clinical MRI study. Consecutive patients entering this study were asked if they were willing to participate in the reproducibility study and have a second MR session. All patients were in good clinical condition and had a stable renal function for a period of at least 3 months prior to the investigations (creatinine clearances ranging between 22.3 ml/min and 94.2 ml/min, median 62.5 ml/min). Patients with diseased renal transplants, who usually do not have stable renal function, were not included. None of the patients were on diuretics. Immunosuppressive drug regimes consisted of Azathioprine and Prednisone in one patient, Cyclosporine in three patients, and Tac...

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