Development of a lipoprotein based molecular imaging MR contrast agent for the noninvasive detection of early atherosclerotic disease.

INTRODUCTION: Currently there are no clinically available means of noninvasively detecting early atherosclerotic disease because these lesions are characterized by an accumulation of extracellular lipid and foam cells, but a lack of significant wall thickening or architectural distortion. OBJECTIVE: We hypothesize that a paramagnetically labeled low density lipoprotein (LDL) could serve as a functional probe to detect sites of abnormal lipid metabolism in the vessel wall that represent sites of early disease. METHODS: Isolated LDL was first incubated with manganese-mesoporphyrin, a hydrophobic MR contrast agent (MnMeso). Size exclusion chromatography and absorption mass spectroscopy were performed on the resulting samples to prove that an association between the two occurred. Subsequently, foam cell cultures (n=7) were incubated (10-30 microg/ml for 48 h) with these labeled lipoproteins and the T1 relaxivity of centrifuged pellets of these cells was determined by using an inversion recovery sequence on a 1.5T scanner. These results were compared to control measurements made from foam cell cultures fed unlabeled lipoproteins (n=7). RESULTS: Measured T1 relaxation times of the cells fed the MnMeso-LDL (443.3 +/- 51.8 ms) was significantly different from the T1 relaxivity obtained from cells fed unlabeled lipoproteins (661.3 +/- 60.9 ms). These findings indicate that the amount of contrast bound to the constructed lipoproteins is sufficient to produce measurable MR signal changes noninvasively. CONCLUSIONS: The study results support the feasibility of future in vivo MR experiments with labeled lipoproteins to assess lipoprotein kinetics in the vessel wall, which will hopefully provide a means of detecting early atherosclerotic disease.

Significance of hyperattenuating and contrast-enhancing hepatic nodules detected in the cirrhotic liver during arterial phase helical CT in pre-liver transplant patients: radiologic-histopathologic correlation of explanted livers.

BACKGROUND: Hyperattenuating nodules detected by arterial phase helical computed tomography (HCT) in patients with cirrhosis usually are believed to represent hepatocellular carcinomas (HCCs). We correlated HCT morphology of hyperattenuating hepatic nodules detected during arterial phase scans with the histopathology of explanted livers of patients with hepatic cirrhosis undergoing liver transplantation. METHODS: Three hundred fifty-four patients had arterial and portal phase HCT performed before subsequent hepatic transplantation. Each patient received 180 mL of contrast by power injection at 5 mL/s. All hyperattenuating nodules detected on arterial phase HCT were assessed for morphology and evidence for contrast enhancement. Explanted livers in all patients were then sectioned at 10-mm intervals, and the histology of the nodules was correlated with the HCT findings. RESULTS: Sixty-one hyperattenuating nodules were detected on the arterial phase HCT in 43 patients: 41 nodules were benign regenerating nodules (RN), three were dysplastic nodules (DP), and 17 were HCCs. Most RN/DP nodules were 5-20 mm in diameter, had distinct margins, were homogeneous, and were isoattenuating on precontrast, portal, and delayed scans. Thirty-six showed positive contrast enhancement and displayed a wide range of attenuation profiles. HCC nodules were 6-50 mm. All showed positive contrast enhancement and displayed a wide range of attenuation profiles. CONCLUSION: Hyperattenuating nodules seen on arterial phase HCT are likely to be RN/DP nodules. In many cases, it is not possible to distinguish between RN/DP and HCC. Thus, clinical decisions regarding inclusion criteria for transplantation based on CT morphology of liver lesions may be tenuous.

Computed tomography-guided neurolytic celiac plexus block with alcohol complicated by superior mesenteric venous thrombosis.

Neurolytic celiac plexus block (CPB) under radiological guidance is often performed to manage pain associated with pancreatic cancer. Serious complications related to the block are rare. Computed Tomography (CT)-guided neurolytic CPB is advocated to improve the efficacy of the block and to reduce the incidence of associated complications. We describe a case of superior mesenteric vein thrombosis associated with neurolytic CPB performed under CT guidance.

Retrospective comparison of the patency of Wallstents and Palmaz long-medium stents used for TIPS. Transjugular intrahepatic portosystemic shunts.

PURPOSE: To compare patency rates of transjugular intrahepatic portosystemic shunts (TIPS) after placement of long-medium Palmaz stents or Wallstents. METHODS: We performed a retrospective review of TIPS performed at our institution between December 1997 and December 1998. During this time period we placed long-medium Palmaz stents for TIPS procedures in 17 patients and Wallstents in 20 patients as the initial stent. Patency was determined on follow-up by ultrasound, angiography, or pathologic examination in the event of transplant. RESULTS: Primary patency in the Palmaz stent group was 70.6% (12/17 patients) (follow-up 1-399 days, mean 127 days). Both primary assisted and secondary patency in the Palmaz group was 100% (17/17 patients) (follow up 1-399 days, mean 154 days). Primary patency in the Wallstent group was 50% (10/20 patients) (follow up 1-370 days, mean 65 days). Primary assisted patency in the Wallstent group was 80% (16/20 patients) (follow up 1-601 days, mean 141 days). Secondary patency in the Wallstent group was 100% (20/20 patients) (follow up 2-601 days, mean 142 days). Kaplan-Meier analysis of the two groups of patients yielded a primary patency of 266 days (standard error 45 days) for TIPS with the Palmaz stent and 139 days (standard error 45 days) for the Wallstent (p =.04). The 3, 6, and 12-month primary patency rates were .84, .63, and .42 respectively for the Palmaz stents and .36, .36, and .18 respectively for the Wallstent. There was no significant difference in primary assisted or secondary patency between the two stent groups. The mean tract curvature in the patients with Palmaz stents was 23.5 degrees (SD 18.2 degrees, range 0-69.0 degrees ) compared with 57 degrees (SD 34.5 degrees, range 7.0-144.0 degrees ) in patients with Wallstents (p =.01). CONCLUSIONS: Our nonprospective, nonrandomized study suggests that TIPS created with the long-medium Palmaz stent have a higher primary patency than those created with the Wallstent in tracts that are relatively straight.

Efficacy and safety of mangafodipir trisodium (MnDPDP) injection for hepatic MRI in adults: results of the U.S. Multicenter phase III clinical trials. Efficacy of early imaging.

The efficacy of contrast-enhanced magnetic resonance imaging (MRI) for detecting and characterizing, or excluding, hepatic masses was assessed in 404 patients, following the intravenous administration of mangafodipir trisodium (MnDPDP) injection, a hepatic MRI contrast agent. An initial contrast-enhanced computed tomography (CT) examination was followed by unenhanced MRI, injection of MnDPDP (5 micromol/kg IV), and enhanced MRI at 15 minutes post injection. Agreement of the radiologic diagnoses with the patients' final diagnoses was higher for enhanced MRI and for the combined unenhanced and enhanced MRI evaluations than for unenhanced MRI alone or enhanced CT using the clinical diagnosis as the gold standard. Mangafodipir-enhanced MRI uniquely provided additional diagnostic information in 48% of the patients, and patient management was consequently altered in 6% of the patients. MnDPDP-enhanced MRI was comparable or superior to unenhanced MRI and enhanced CT for the detection, classification, and diagnosis of focal liver lesions in patients with known or suspected focal liver disease.

Venous thrombosis and occlusion after pancreas transplantation: evaluation with breath-hold gadolinium-enhanced three-dimensional MR imaging.

OBJECTIVE: We describe the imaging findings of venous thrombosis and occlusion after pancreatic transplantation in five patients who underwent multiphasic breath-hold gadolinium-enhanced three-dimensional MR imaging. CONCLUSION: Venous thrombus appeared as serpetine voids within the graft parenchyma or at the venous anastomosis during the venous phase of MR imaging. Nonenhancement or heterogeneous enhancement of graft parenchyma corresponded to glandular necrosis at pancreatectomy in two patients. Initial sonographic evaluation was nondiagnostic of venous thrombosis in two of five patients. Multiphasic breath-hold gadolinium-enhanced three-dimensional MR imaging of pancreatic transplants can provide information to make the specific diagnosis of venous thrombosis or occlusion.

Time-of-flight MR angiography with Gd-DTPA hexamethylene diamine co-polymer blood pool contrast agent: comparison of enhanced MRA and conventional angiography for arterial stenosis induced in rabbits.

Vascular stenoses were induced in the external iliac arteries of New Zealand white rabbits by a combination of hypercholesterolemic diet and repeat balloon injury. Two-dimensional (2D) and three-dimensional (3D) time-of-flight (TOF) magnetic resonance angiography (MRA) was performed with a specifically designed phased array coil in a 1.5 T system. Enhancement with gadolinium-diethylene triamine pentaacetic acid (Gd-DTPA) hexamethylene diamine co-polymer (Nycomed: NC 22181), a blood pool MR contrast agent, was measured after contrast administration and compared with pre-contrast images at the same levels. Vessel diameter measurements were obtained at multiple levels and compared with comparable levels on conventional angiograms of the same animals. Stable enhancement, averaging 227% above baseline, was observed with the 3D TOF MRA over the 40 minutes of this study. Enhancement was not observed with the 2D TOF technique. Measurement of the smallest vessels in this study with 3D TOF MRA was slightly improved following contrast enhancement, although both pre- and post-contrast diameter measurements tended to underestimate the assumed true vessel diameter. Thus, Gd-DTPA hexamethylene diamine co-polymer (Nycomed: NC 22181), a blood pool MR contrast agent, produces significant, stable enhancement with the 3D TOF technique and may improve MRA measurement of small vessels.

Primary placement of Palmaz long medium stents in transjugular intrahepatic portosystemic shunts.

PURPOSE: To describe our results with primary placement of the long-medium Palmaz stent for transjugular intrahepatic portosystemic shunts (TIPS). MATERIALS AND METHODS: Between December 1997 and December 1998 primary placement of long-medium Palmaz stents was performed for TIPS procedures in 17 patients. Patency was determined with ultrasound, angiography, or pathologic examination in the event of transplant. RESULTS: Primary patency was achieved in 13 of 17 patients (76.5%) (follow up, 1-399 days; mean, 99 days). Secondary patency was achieved in 17 of 17 patients (100%) (follow-up, 1-399 days; mean, 110 days). Among the four patients who required revision, the mean time to revision from initial shunt creation was 81 days (range, 13-125 days). Two of these four patients had symptoms of worsening ascites as well as abnormal ultrasound findings prior to their revision; the other two patients were asymptomatic and had abnormal ultrasound findings only. Revisions were performed for intimal hyperplasia within the stent in three of the patients and acute thrombus within the stent in the remaining patient. Kaplan-Meier survival analysis for primary patency yielded mean survival time of 265 days (standard error, 52 days). CONCLUSION: The long-medium Palmaz stent is a viable stent for creation of TIPS shunts.

Sonographic detection of acute parenchymal injury in an experimental porcine model of renal hemorrhage: gray-scale imaging using a sonographic contrast agent.

OBJECTIVE: The purpose of this study was to determine the usefulness of contrast-enhanced sonography in the detection of acute parenchymal injury. SUBJECTS AND METHODS: In a model of acute renal injury in pigs, four separate renal parenchymal bleeds were created by puncturing an interlobar artery of the upper and lower poles of the kidneys. B-mode gray-scale scans of the kidneys before and after injury, and after the administration of i.v. and intraarterial (i.a.) contrast agents were recorded on videotape for 5 min for each condition (baseline, after injury, after i.v. contrast administration, and after i.a. contrast administration). For each condition and injury, selected frames were analyzed with regions of interest of the normal renal parenchyma, the area of injury, and the perinephric space. Randomized videotape clips from each of the experimental conditions were rated by three sonologists as to the presence or absence of increased intrarenal parenchymal echogenicity, perinephric echogenicity, and confidence as to whether renal injury was present. RESULTS: Areas of renal injury were isoechoic with normal parenchyma on unenhanced scans. After both i.v. and i.a. contrast material injection, areas of injury were visible as areas of increased echogenicity. Contrast increased from 0.2 on unenhanced images to 4.0 and 4.5, respectively, after i.v. and i.a. administration of the new contrast agent. The three observers' ability to diagnose renal injury increased from 0.61, 0.64, and 0.54 to 0.71, 0.70, and 0.74 after i.v. injection and to 0.93, 0.92, and 0.97 after i.a. injection as indicated by the area under the curve in the receiver operating characteristic analysis. CONCLUSION: Transabdominal contrast-enhanced gray-scale sonography can reveal the area of acute renal hemorrhage. This procedure may be applicable in patients when sonographic contrast agents, imaging procedures, and modes of contrast administration are optimized for clinical use in trauma.

Association with oleic acid vesicles enhances manganese III mesoporphyrin absorption and biliary elimination in rats.

OBJECTIVE: To determine whether the association of manganese III mesoporphyrin (MnMeso), an oral MR contrast agent, to oleic acid (OA) vesicles will improve absorption and delivery of MnMeso to the liver. METHODS: MnMeso or MnMeso-OA vesicle suspension was intraduodenally administered to rats and the time course of MnMeso concentration in plasma, bile, and intestinal solution was determined. Tissue concentrations of MnMeso in the liver were also determined. RESULTS: Association of MnMeso to OA reduced the time it took to reach one-half absorption maximum, TC50, and enhanced the rate and the extent of biliary elimination of this contrast agent. In addition, the results obtained from dose-titration studies indicate that MnMeso-OA vesicle complex may enhance MnMeso accumulation in the liver, observed as a lower dose required to reach equivalent tissue concentration. Taken together, complexion to OA vesicles may provide rapid absorption, enhanced liver accumulation, and efficient elimination of MnMeso. CONCLUSIONS: Association with OA vesicles may enhance the rate of MnMeso absorption and biliary excretion while promoting the extent of liver accumulation of MnMeso in rats. This strategy may provide a means to provide safe and effective use of MnMeso as an MR contrast medium.

CT blood pool enhancement in primates with lopromide-carrying liposomes containing soy phosphatidyl glycerol.

RATIONALE AND OBJECTIVES: The purpose of this study was to determine the feasibility of using iodinated liposomes as blood pool agents for computed tomography (CT) in nonhuman primates. MATERIALS AND METHODS: Five normal adult baboons (15-21 kg) were anesthetized and intravenously injected with iopromide containing soy phosphatidyl glycerol liposomes with a diameter of 195 nm. Each animal received a dose of 300 mg total iodine per kilogram (46% encapsulation). RESULTS: The animals tolerated the injections well, experiencing no measurable electrocardiographic changes, and recovered uneventfully from anesthesia. Sequential helical CT scans of the baboons from the base of the skull to the symphysis pubis acquired up to 40 minutes after injection showed persistent blood pool enhancement. Maximum mean enhancement of major vascular structures was 106 HU at 1 minute after contrast medium injection. Mean blood pool enhancement was 76, 72, and 67 HU at 10, 20, and 40 minutes after injection, respectively. Liver and spleen were enhanced by 40 and 41 HU, respectively, 40 minutes after injection. No significant enhancement was measured in the brain and pancreas. CONCLUSION: Soy phosphatidyl glycerol with iopromide liposomes produces prolonged vascular enhancement and has potential as a blood pool CT contrast agent in primates.

Black blood magnetic resonance angiography with Dy-DTPA polymer: effect on arterial intraluminal signal intensity, lumen diameter, and wall thickness.

Four rabbits in which atherosclerotic disease was induced by diet and balloon angioplasty underwent conventional angiography and MR angiography (MRA) using a black blood pulse sequence before and 10 minutes after the i.v. injection of a macromolecular contrast agent, NC 100283 (1.0 mmol/kg), a dysprosium diethylenetriaminepentaacetic acid hexamethylenediamine copolymer (Dy-DTPA polymer). Intraluminal signal intensity, apparent wall thickness, and lumen size measurements of the aorta and proximal common iliac arteries on precontrast MRA images were compared with postcontrast images. Aortic lumen diameter measurements on the precontrast and postcontrast MRA studies were compared with lumen diameters from conventional angiograms. Intraluminal signal intensity decreased on postcontrast MRA images compared with precontrast images, with an average loss of signal equal to 29% (P < .05). Apparent wall thickness decreased by 24% (P < .05). Lumen diameter and area were generally larger (average of 15% and 33%, respectively) on postcontrast MRA images than on precontrast images. Aortic lumen diameter measurements from postcontrast MRA agreed closely (95% confidence interval of the mean difference was -.2 to .3 mm), and precontrast MRA images tended to underestimate aortic lumen diameter (95% confidence interval of the mean difference was .3 to .8 mm) compared with conventional angiography. Postcontrast MRA with NC 100283, a macromolecular Dy-DTPA contrast agent, provides more accurate assessment of aortic lumen diameter than precontrast MRA, using conventional angiography as the standard reference.

Imaging of oncologic patients: benefit of combined CT and FDG PET in the diagnosis of malignancy.

OBJECTIVE: The purpose of this study was to assess the benefit of combined CT and 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) in diagnosing malignancy. MATERIALS AND METHODS: The records of 26 patients with intraabdominal and intrathoracic neoplasms who underwent CT and FDG PET between January 1995 and September 1996 were retrospectively reviewed. Most of these patients had inconclusive findings on prior CT for the diagnosis of malignancy. Only sites of potential malignant disease were included in the data analysis. Presence or absence of malignancy was confirmed by histopathology or follow-up CT. Three observers experienced in abdominal imaging used CT findings alone to estimate level of suspicion (1 = definitely not malignant to 5 = definitely malignant) for primary or recurrent neoplasms (n = 21), distant metastases (n = 25), and neoplastic nodal involvement (n = 18). Six weeks later the three observers reviewed the same CT examinations supplemented with FDG PET and reestimated suspicion of malignancy. Receiver operating characteristic methodology was used to analyze the results. Sensitivity, specificity, positive and negative predictive values, and accuracy in diagnosis of malignant disease were calculated using level 4 (probable malignancy) as the cutoff for the presence of disease. RESULTS: The mean area under the receiver operating characteristic curve, indicating successful diagnosis of malignancy, was .82 for CT alone and .92 for CT with FDG PET (p < .05). The accuracies for diagnosis of primary or recurrent neoplasms, distant metastases, and neoplastic nodal involvement were 62%, 68%, and 83%, respectively, for CT alone and 81% (p = .06), 88% (p = .03), and 89% (p > .25), respectively, for CT with FDG PET. Also, supplemental FDG PET imaging improved observer confidence and accuracy in diagnosing recurrent neoplasm in four (36%) of 11 patients who had undergone surgery or chemoradiation and in diagnosing four (29%) of 14 extrahepatic sites that had potential metastases. CONCLUSION: Diagnosis of malignancy in oncologic patients is significantly improved when CT is supplemented with FDG PET. Combined imaging is particularly helpful in the evaluation of potential recurrence in previously treated patients and for diagnosing extrahepatic lesions that may be distant metastases.

Pancreatic arterial anatomy: depiction with dual-phase helical CT.

PURPOSE: To determine the efficacy of arterial phase helical computed tomography (CT) for the depiction of small pancreatic arteries. MATERIALS AND METHODS: Arterial phase helical CT (3-mm collimation, 1-mm reconstruction interval) was performed during power injection of 180 mL of ioversol at 5 mL/sec. Two radiologists reviewed 100 consecutive arterial phase helical CT scans of the pancreas in patients with normal glands and recorded the frequency of visualization of the major visceral (celiac, hepatic, splenic, gastroduodenal, superior mesenteric) and small pancreatic (dorsal pancreatic, right branch of the dorsal pancreatic, pancreaticomagna, caudal pancreatic, transverse pancreatic, anterior and posterior arcade, and inferior pancreaticoduodenal) arteries. RESULTS: Scans in 87 patients were technically satisfactory and were included in the analysis. The major visceral arteries were seen in all patients. The following secondary pancreatic arteries were seen: dorsal pancreatic, 82 (94%) patients; pancreaticomagna, 45 (52%); caudal pancreatic, 34 (39%); transverse pancreatic, 36 (41%); right branch of the dorsal pancreatic, eight (9%); anterior arcade, 47 (54%); posterior arcade, 63 (72%); and inferior pancreaticoduodenal, 73 (84%). CONCLUSION: Small pancreatic arteries can be delineated on arterial phase helical CT scans by using optimized techniques.

Frontal lobe shortening in second-trimester fetuses with trisomy 21: usefulness as a US marker.

PURPOSE: To determine whether the frontal lobe is disproportionately smaller than normal in second-trimester fetuses with Down syndrome by using prenatal ultrasonographic (US) measurements of the frontothalamic distance (FTD). MATERIALS AND METHODS: The FTD, measured from the inner table of the frontal bone to the posterior margin of the thalamus, was measured in 43 fetuses (mean gestational age, 17.2 weeks +/- 1.3 [standard deviation]; range, 15.0-20.4 weeks) with chromosomally proved trisomy 21 and in 160 chromosomally normal fetuses (mean gestational age, 17.1 weeks +/- 1.5; range, 14.5-22.5 weeks). Other cranial biometric ratios also were calculated. RESULTS: The FTD was best predicted from the estimated gestational age (EGA) in the euploid population with the quadratic equation FTD = -0.0120 x EGA2 + 0.6917 x EGA - 5.2349 (R2 = .731) or from the biparietal diameter (BPD) with the linear equation FTD = 0.6837 x BPD + 0.5525 (R2 = .731). If an observed-to-expected ratio of 0.84 is used as a cutoff sign to screen for trisomy 21, a sensitivity of 16%, specificity of 97%, odds ratio of 6.03 (95% confidence interval, 1.81, 20.1), and relative risk of 5.98 are achieved. CONCLUSION: The frontal lobe is statistically significantly smaller in fetuses with trisomy 21. US measurement of the FTD may prove to be a useful adjunctive screening tool if used with other markers for Down syndrome.

Assessment of fetal and placental blood flow in primates using contrast enhanced ultrasonography.

Ultrasonographic contrast agents that stay within the vascular space and do not cross the placenta may permit differentiation between the maternal and fetal portions of the placenta and may be clinically useful for diagnosis of placental abnormalities. This study was performed to assess the effects of Levovist (Schering AG, Berlin) on the placental circulation and to determine whether hemodynamic effects on the fetus occur. Ten studies were performed in five pregnant macaques (median weight, 9.15 kg; range, 6.15 to 11 kg; median gestational age, 121 days; range, 34 days to term) under anesthesia. Gray scale, color, and duplex Doppler sonographic scans of the fetus and placenta were acquired using a 5 MHz curved array transducer. Fetal heart rate, resistive index, and systolic-diastolic ratios were measured in the fetal middle cerebral artery, aorta, umbilical artery, and uterine artery before and after administration of contrast agent. The following dose regimen was tested: 5 ml of physiologic saline solution followed by 0.1 ml/kg of 300 mg/ml Levovist (diagnostic dose), 0.5 ml/kg of 400 mg/ml Levovist (maximum dose), and 5 ml physiologic saline solution. The order of diagnostic dose and maximal dose was randomized among animals. Color enhancement of the basal portions of the placenta was documented after administration of contrast agent. Heart rate and middle cerebral artery systolic-diastolic ratio did not change between baseline and injections. A 7% decrease of the resistive index from baseline to maximum dose was measured in the uterine artery (not significant). A 7.7% decrease in the systolic-diastolic ratio from baseline to maximum dose was recorded in the umbilical artery. However, an identical change was measured after saline solution was injected. The resistive index in the aorta increased by 2.6% from baseline to maximum dose, a change that was not significant (P > 0.5). Ultrasonographic contrast enhancement of the maternal circulation in placenta is demonstrated to be without significant effects on the fetal circulation as measured in this limited population.

Detection and characterization of atherosclerotic fibrous caps with T2-weighted MR.

PURPOSE: We assessed the performance of T2-weighted MR imaging in detecting atherosclerotic fibrous caps and in depicting their integrity. METHODS: Twenty atherosclerotic lesions removed by carotid endarterectomy were imaged on a 1.5-T system using T2-weighted spin-echo sequences. The MR images were reviewed independently by four blinded interpreters for fibrous caps and ruptures. The results obtained from the observers were then graded against histologic findings by using receiver-operating characteristic (ROC) curve analysis. RESULTS: The area under the ROC curve for fibrous cap detection was 0.80, indicating that T2-weighted MR imaging was a good but not definitively diagnostic test for detecting ex vivo fibrous caps. The ROC curve for fibrous cap characterization yielded an area of 0.75, indicating that T2-weighted MR imaging was a fair but not highly diagnostic test for depicting fibrous cap integrity. A definite reading for detection of fibrous caps or rupture was fairly specific (90% and 98%, respectively) but not very sensitive (37% and 12%, respectively). CONCLUSIONS: T2-weighted MR imaging of ex vivo atherosclerotic plaques aided in the detection and evaluation of fibrous caps. In both cases, MR imaging proved more useful for ruling out disease than for confirming its presence.

Characterization of atherosclerotic plaques at the carotid bifurcation: correlation of high-resolution MR imaging with histologic analysis--preliminary study.

The clinical symptoms and morbidity that result from carotid artery disease, the primary cause of stroke, are mainly due to plaque ulceration, thrombosis, intraplaque hemorrhage, and thinned fibrous caps. The contents of atherosclerotic plaques of the carotid artery can be determined with in vivo high-resolution magnetic resonance imaging with flow suppression. Eight patients scheduled to undergo endarterectomy and four healthy volunteers were imaged with a 1.5-T imager and custom-made carotid phased-array coils. T1-weighted spin-echo images and cardiac-gated proton-density--weighted fast spin-echo images were acquired. In vivo imaging findings as determined by three radiologists were correlated with ex vivo imaging and histologic findings. Among the eight plaque specimens, regions of hemorrhage, calcium, lipid deposits, and fibrous plaques were identified on T1- and proton-density-weighted images. Calcium and lipid deposits were detectable on both T1- and proton-density--weighted images. Hemorrhage and fibrous plaques were better demonstrated on proton-density--weighted images.

Intestinal absorption of Mn-mesoporphyrin in a small bowel sac system: effect of oleic acid.

RATIONALE AND OBJECTIVES: The authors investigated the effect of oleic acid (cis-9-octadecenoic acid) (OA), a lipidic carrier, on the intestinal absorption rate and T1 relaxation time of manganese (III) mesoporphyrin (Mn-mesoporphyrin), a prototype hepatobiliary contrast agent for magnetic resonance imaging. METHODS: Mn-mesoporphyrin was formulated with OA at various concentrations. Small bowel sacs were created in 36 rats and filled with complexed and free Mn-mesoporphyrin. Intestinal absorption of Mn-mesoporphyrin was measured with spectrophotometry at 364 nm. T1 relaxation times were measured in samples of Mn-mesoporphyrin solutions, bowel wall, liver, and bile. RESULTS: Absorption rates ranged from 4.2%/cm2/h to 13%/cm2/h. Absorption was greatest (13%/cm2/h) when a combination of 1 mmol/L Mn-mesoporphyrin and 26.5 mmol/L OA was used. The T1 of bile decreased from 2,480 to 248 msec (maximum decrease) in rats that received Mn-mesoporphyrin. CONCLUSION: Mn-mesoporphyrin is absorbed from the small bowel in both the lipid-associated and free form, resulting in substantial shortening of the T1 in bile.