Evaluation of hepatocyte-specific paramagnetic contrast media for MR imaging of hepatitis

The hepatocyte-specific paramagnetic magnetic resonance (MR) contrast agents manganese-DPDP [N,N′-dipyridoxylethylenediamine-N,N′-diacetate 5,5′ bis-(phosphate)] and gadobenate dimeglumine were used for diagnosing chemically induced hepatitis in rats. Ex vivo liver tissue relaxation times and in vivo MR image signal-to-noise ratios were compared before and after contrast agent administration. Ex vivo relaxometry and in vivo MR imaging showed that Mn-DPDP enhanced normal and diseased livers to the same degree at all time points from 5 to 120 minutes. Gadobenate dimeglumine showed reduced T1 and T2 enhancements in hepatitis relative to those of normal liver, in the early phase (5–30 minutes). However, these effects are offsetting, and as a result, MR imaging failed to allow distinction of diseased from normal livers. This surprising result observed in vivo was in fact predicted by applying the Bloch equation to our ex vivo data. Our results show that detection and quantitation of hepatitis with MR imaging enhanced with paramagnetic cellspecific contrast agents will be more difficult than anticipated.     

Enhanced tumor detection in the presence of fatty liver disease: Cell-specific contrast agents

It is assumed that hepatobiliary, cell-specific contrast agents will be adversely affected by the presence of diffuse liver disease. The diagnostic efficacy for tumor detection in the presence of fatty liver disease was experimentally studied at contrast-enhanced magnetic resonance (MR) imaging with manganese-DPDP (N,N′-dipyridoxylethylenediamine-N,N′-diacetate 5,5′-bis[phosphate]) and gadobenate dimeglumine (Gd-BOPTA/dimeg) and compared with conventional and chemical shift imaging. Carcinosarcoma was implanted into the liver of rats, and fatty liver was induced with L-ethionine. Without contrast agents, the tumor-fatty liver contrast-to-noise ratio (C/N) was increased on T1-weighted and decreased on T2-weighted MR images relative to tumor-bearing control rats without fatty liver. Chemical shift imaging (phase-contrast method) increased the tumor—fatty liver C/N from 2.3 ± 1.0 to 6.1 ± 1.7 (P <.001). Mn-DPDP and Gd-BOPTA/dimeg increased the tumor—fatty liver C/N from -5.4 ± 1.6 to -11.0 ± 1.9 and ?9.8 ± 3.4, respectively (P <.001). The hepatobiliary, cell-specific contrast agents were equally effective in both fatty and nonfatty liver and outperformed both chemical shift and conventional MR imaging in detecting liver tumors.     

Mn-DPDP–enhanced MR imaging of malignant liver lesions: Efficacy and safety in 20 patients

Twenty patients with malignant liver lesions underwent magnetic resonance (MR) imaging with manganese (II) DPDP [N,N′-dipyridoxylethylenediamine-N,N′-diacetate 5,5′-bis(phosphate)] to evaluate the safety and efficacy of the contrast agent. In two groups of 10 patients each, 5 μmol/kg Mn-DPDP was administered intravenously (3 mL/min) at a concentration of either 50 or 10 μmol/mL. T1- and T2-weighted images were obtained with a 1.5-T imager. Six patients reported a total of eight instances of side effects (flush, feeling of warmth, metallic taste) of which seven occured at the 50 μmol/mL concentration. A significant decrease in alkaline phosphatase levels 2 hours after injection was recorded. On T1-weighted images, the 10 μmol/mL formulation yielded significantly greater increases in contrast-to-noise ratio (79.8%–137.5%) than the 50 μmol/mL formulation (46.2%–86.6%). In a blinded reader study of 10 patients with one to five lesions each, no lesion was missed on Mn-DPDP–enhanced T1-weighted images; however, four false-positive foci were identified. The authors conclude that slow administration of 5 μmol/kg Mn-DPDP at a concentration of 10 μmol/mL is safe and efficient enough to proceed to further clinical trials.     

Gd-EOB-DTPA enhanced MR imaging: Evaluation of biliary and renal excretion in normal and cirrhotic livers

Objective

The purpose of this study was to assess the difference in the activity of biliary and renal excretion between normal and cirrhotic livers on contrast-enhanced MR imaging obtained with gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid (Gd-EOB-DTPA).

Methods

A total of 78 patients with cirrhotic liver (n = 44) and with normal liver (n = 34) underwent multi-phase Gd-EOB-DTPA enhanced MR imaging (arterial, portal, equilibrium, and three hepatobiliary phases (10, 15 and 20 min HP), respectively), and these contrast-enhanced images were qualitatively and quantitatively evaluated for the differences of the biliary and renal excretion between normal and cirrhotic livers.

Results

The timing of biliary excretion of contrast agents in the cirrhotic liver was significantly slower than that in the normal liver (P < 0.001). The degree of contrast enhancement in the common bile duct in the normal liver was significantly better than that in the cirrhotic liver (P = 0.003). Contrast agents were demonstrated in the duodenum at 20 min HP in 8/44 (18%) cirrhotic liver while they were seen in 15/34 (44%) normal liver (P = 0.013). The enhancement effects of renal medulla and portal vein at 20 min HP in the cirrhotic liver were significantly higher than those of normal liver (P = 0.043 and P < 0.001, respectively).

Conclusion

Biliary excretion of Gd-EOB-DPTA was impaired in cirrhotic livers in comparison with normal livers while renal excretion of Gd-EOB-DPTA was increased.     

Human fascioliasis: MR imaging findings of hepatic lesions

Our objective was to describe MR imaging findings of liver lesions in human fascioliasis. The MR imaging of the liver was performed in 29 patients with fascioliasis. Seventeen patients were women and 12 were men, with a mean age of 47.5 years (age range 17–75 years). Hepatic lesions were grouped into five types based on their signal characteristics. Three patients had normal imaging findings. One or more lesions were observed in the other 26 patients. The lesion types and the frequency of appearances were as follows: hyperintensity of the liver capsule on T2-weighted images (n=16, 55.2%); ill-defined slightly hyperintense areas on T2-weighted images (n=18, 62.1%); lesions which were hypointense on T1-weighted and hyperintense on T2-weighted images (n=10, 34.5%); hypointense on T1-weighted images and centrally hypo- or hyperintense, surrounded by peripherally less hyperintense area on T2-weighted images (n=4, 13.8%); and hypointense foci or ill-defined hypointense areas on T1- and T2-weighted images (n=10, 34.5%). We describe the MR imaging features of the disease. Our findings may help the differential diagnosis in which fascioliasis should be added to the list. Electronic Publication     

Malignant lesions of the liver identified on T1- but not T2-weighted MR images at 1.5 T

The authors reviewed their 21/2-year experience with a magnetic resonance (MR) imaging protocol for a 1.5-T MR imager that included T2-weighted fat-suppressed spin-echo, T1-weighted breath-hold gradient-echo, and serial dynamic gadolinium-enhanced T1-weighted gradient-echo imaging to identify histologic types of malignant liver lesions more apparent on T1- than on T2-weighted images. MR images of 212 consecutive patients with malignant liver lesions were reviewed. T2-weighted, T1-weighted, and dynamic contrast-enhanced T1-weighted images were examined separately in a blinded fashion. Seven patients demonstrated liver lesions (lymphoma [two patients] and carcinoid, hepatocellular carcinoma, colon adenocarcinoma, transitional cell carcinoma, and melanoma [one patient each]) on T1-weighted images that were inconspicuous on T2-weighted images. In all cases, the lesions were most conspicuous on T1-weighted images obtained immediately after administration of contrast agent. Histologic confirmation was present for all seven patients. The consistent feature among these lesions was that they were hypovascular, due either to a fibrous stroma or to dense monoclonal cellularity. These results suggest that in some patients with hypovascular primary neoplasms, the lesions may be identified only on T1-weighted images, and that immediate postcontrast T1-weighted images are of particular value in demonstrating lesions.     

Diagnosis of fatty liver with MR imaging.

The diagnosis of fatty liver with magnetic resonance (MR) imaging was evaluated in experimental rat models of simple fatty infiltration and fatty liver with hepatocellular injury. T1 and T2 were measured ex vivo and correlated with the histologic degree of fatty infiltration. Enhancement of fatty liver with four different cells-specific contrast agents was studied with ex vivo relaxometry and in vivo MR imaging. Quantitative analysis of conventional and chemical shift MR images was correlated with biochemically determined fat content of the liver. Diet-induced simple fatty infiltration of the liver caused a decrease in T1 of 15%, whereas the T1 of L-ethionine-induced fatty liver with hepatocellular injury increased by 12%. T2 showed a positive correlation with the degree of fatty infiltration in both models. Cell-specific hepatobiliary contrast agents showed the same liver uptake and relaxation enhancement in fatty livers as in normal livers. Conventional T1-weighted images and chemical shift images showed good correlation (r = .83 and .80, respectively) between signal intensity and the degree of fatty infiltration. However, only chemical shift imaging was reliable in the diagnosis of fatty liver.     

Segmental hyperintensity on T1-weighted MRI of the liver: Indication of segmental cholestasis

The purpose of this study was to determine the relationship between segmental hyperintensity of the liver on T1-weighted images and segmental cholestasis in patients with obstructive jaundice. T1-weighted and T2-weighted MR images were obtained of 73 patients with obstructive jaundice caused by various diseases. Fat-suppressed T1-weighted images were also obtained of 10 patients. Eleven patients with segmental intra-hepatic bile duct dilatation (cholestasis) showed segmental hyperintensity on T1-weighted images and/or fat-suppressed T1-weighted images and no signal intensity difference on T2-weighted images. Sixty-two patients with widespread intrahepatic bile duct dilatation showed no intensity difference on T1-weighted and T2-weighted images (P < .01). Segmental hyperintensity on T1-weighted images was correlated with intrahepatic cholestasis.     

Gadobenate Dimeglumine as an Intrabiliary Contrast Agent: Comparison with Mangafodipir Trisodium with Respect to Non-dilated Biliary Tree Depiction

Objective

To compare the efficacy of Mangafodipir trisodium (Mn-DPDP)-enhanced MR cholangiogrphy (MRC) and Gadobenate dimeglumine (Gd-BOPTA)-enhanced MRC in visualizing a non-dilated biliary system.

Materials and Methods

Eighty-eight healthy liver donor candidates underwent contrast-enhanced T1-weighted MRC. Mn-DPDP and Gd-BOPTA was used in 36 and 52 patients, respectively. Two radiologists reviewed the MR images and rated the visualization of the common duct, the right and left hepatic ducts, and the second-order branches using a 4-point scale. The contrast-to-noise ratio (CNR) of the common duct to the liver in the two groups was also compared.

Results

Mn-DPDP MRC and Gd-BOPTA MRC both showed similar visualization grades in the common duct (p = .380, Mann-Whitney U test). In the case of the proximal bile ducts, the median visualization grade was significantly higher with Gd-BOPTA MRC than with Mn-DPDP MRC (right hepatic duct: p = 0.016, left hepatic duct: p = 0.014, right secondary order branches: p = 0.006, left secondary order branches, p = 0.003). The common duct-to-liver CNR of the Gd-BOPTA MRC group was significantly higher (38.90±24.50) than that of the Mn-DPDP MRC group (24.14±17.98) (p = .003, Student''s t test).

Conclusion

Gd-BOPTA, as a biliary contrast agent, is a potential substitute for Mn-DPDP.     

Magnetic resonance imaging of intramuscular myxoma with histological comparison and a review of the literature

Objective To evaluate the magnetic resonance (MR) features of intramuscular myxoma (IM) compared with its pathological findings.Design Two radiologists retrospectively reviewed records and imaging studies of patients with histologically proven IM. Two radiologists also analyzed by consensus all the MR studies (pre- and post-contrast T1-weighted and T2-weighted sequences) and a pathologist reviewed the available histological material.Patients Seventeen patients with 18 histologically proven IM were reviewed. Histological samples of 11 of these 18 tumors were available for pathological analysis.Results There were 14 women and three men, with a mean age of 58.9 years. IM involved predominantly the thigh (n=10). MR imaging showed well-circumscribed intramuscular masses, hypointense on T1-weighted and hyperintense on T2-weighted images. Eleven masses were homogeneous and seven slightly heterogeneous due to fibrous septa. Enhanced MR imaging demonstrated three different patterns: peripheral enhancement (n=1), peripheral and patchy internal enhancement (n=7) or peripheral and linear internal enhancement (n=4). Intratumoral cysts were detected in four masses. MR imaging showed the presence of a pseudocapsule (n=12), fat around the lesion (n=16) and peritumoral edema (n=16). Histologically, all the tumors were hypocellular, hypovascular and myxoid. Peripheral areas of collagenous fibers formed a partial capsule and IM often merged into surrounding muscular fibers. More cellular tumors and those with scanty myxoid stroma tended to show a more prominent internal enhancement.Conclusion IM shows several recognizable MR features which suggest its diagnosis.     

Characterization of Focal Liver Lesions with Superparamagnetic Iron Oxide-Enhanced MR Imaging: Value of Distributional Phase T1-Weighted Imaging

Objective

To determine the potential value of distributional-phase T1-weighted ferumoxides-enhanced magnetic resonance (MR) imaging for tissue characterization of focal liver lesions.

Materials and Methods

Ferumoxides-enhanced MR imaging was performed using a 1.5-T system in 46 patients referred for evaluation of known or suspected hepatic malignancies. Seventy-three focal liver lesions (30 hepatocellular carcinomas [HCC], 12 metastases, 15 cysts, 13 hemangiomas, and three cholangiocarcinomas) were evaluated. MR imaging included T1-weighted double-echo gradient-echo (TR/TE: 150/4.2 and 2.1 msec), T2*-weighted gradient-echo (TR/TE: 180/12 msec), and T2-weighted turbo spin-echo MR imaging at 1.5 T before and after intravenous administration of ferumoxides (15 mmol/kg body weight). Postcontrast T1-weighted imaging was performed within eight minutes of infusion of the contrast medium (distributional phase). Both qualitative and quantitative analysis was performed.

Results

During the distributional phase after infusion of ferumoxides, unique enhancement patterns of focal liver lesions were observed for hemangiomas, metastases, and hepatocellular carcinomas. On T1-weighted GRE images obtained during the distributional phase, hemangiomas showed a typical positive enhancement pattern of increased signal; metastases showed ring enhancement; and hepatocellar carcinomas showed slight enhancement. Quantitatively, the signal-to-noise ratio of hemangiomas was much higher than that of other tumors (p < .05) and was similar to that of intrahepatic vessels. This finding permitted more effective differentiation between hemangiomas and other malignant tumors.

Conclusion

T1-weighted double-echo FLASH images obtained soon after the infusion of ferumoxides, show characteristic enhancement patterns and improved the differentiation of focal liver lesions.     

Contrast-enhanced MRI of the liver with mangafodipir trisodium: imaging technique and results

Magnetic resonance (MR) contrast agents are now routinely used for detecting and characterizing focal liver lesions. Liver specific, hepatobiliary, MRI contrast agent mangafodipir trisodium (Mn-DPDP) is taken up by the functioning hepatocytes and excreted by the biliary system. Contrast uptake leads to persistent elevation of T1-weighted signal of normal liver parenchyma within 10 minutes of injection. Most tumors of non-hepatocellular origin typically are hypointense relative to enhanced liver parenchyma on T1 weighted images and are more conspicuous than on unenhanced images. Whereas, tumors of hepatocellular origin such as focal nodular hyperplasia (FNH), adenoma, and well-differentiated hepatocellular carcinomas (HCC) have been shown to accumulate Mn-DPDP, providing characterization information to discriminate hepatocellular from non-hepatocellular tumors. The purpose of this pictorial essay is to illustrate the appearance of various liver tumors on mangafodipir enhanced liver MR imaging.     

Gadoteridol dose dependence in MR imaging of a liver abscess model

A necrotic liver abscess model was studied with magnetic resonance (MR) imaging at 1.5 T before and after intravenous administration of gadoteridol at doses of 0.1, 0.25, and 0.5 mmol/kg in 24 rabbits. Enhancement characteristics and lesion delineation were assessed with both breath-hold and non-breath-hold imaging techniques. Lesion delineation, as assessed both by signal intensity measurements and evaluations by two image readers blinded to imaging technique, was greatest on high-dose (0.5 mmol/kg) breath-hold images. Lesion rim enhancement was seen consistently only on postcontrast images obtained at a dose of 0.5 mmol/kg and progressed with time after injection of contrast material.     

Gadolinium-phthalein complexone as a contrast agent for hepatobiliary MR imaging

Gadolinium-phthalein complexone (Gd-PC) was developed as a hepatobiliary magnetic resonance (MR) contrast agent. Phthalein complexone is one of the iminodiacetic acid derivatives and a structural analogue of bromosulfophthalein. Gadolinium-PC substantially enhanced signal intensity of normal functioning livers on T1-weighted MR images. Contrast enhancement of rabbit liver and gradual accumulation of high intensity bile in the gallbladder were observed after intravenous injection of 0.05 and 0.1 mmol/kg Gd-PC. However, 0.1 mmol/kg of Gd-DTPA caused little effect on liver MR.     

Spin-echo and dynamic gadoliniumenhanced flash MR imaging of hepatocellular carcinoma: Correlation with histopathologic findings

Evaluation of histologic subtype and degree of differentiation in hepatocellular carcinoma (HCC) is essential because it affects patient prognosis and treatment planning. To evaluate the histologic subtype of HCC with magnetic resonance (MR) imaging, conventional spin-echo and dynamic studies were correlated with histopathologic and angiographic findings in 72 HCCs. Dynamic MR imaging was performed with the fast low-angle shot (FLASH) technique after administration of gadopentetate dimeglumine. There was considerable overlap in signal intensity between various tumor grades on both T1- and T2-weighted images. On dynamic MR images, the peak contrast enhancement ratio correlated with tumor grade (well-differentiated, 29.5 ± 24.7; moderately differentiated, 63.5 ± 24.1; poorly differentiated, 86.9 ± 26.4) or degree of dilatation of the sinusoidlike vascular space between tumor cells. The maximum contrast-to-noise ratio in tumor (relative to surrounding liver) was achieved within 60 seconds in 45 HCCs (mostly of the trabecular or pseudoglandular type). Enhancement was slight or minimal in 17 tumors (mostly small, well-differentiated tumors). In 10 tumors, the degree of enhancement increased with time, with maximum enhancement in the delayed phase (most frequently in scirrhous HCC). These dynamic patterns correlated with angiographic findings. These data indicate that the degree and pattern of enhancement on dynamic MR images reflect tumor differentiation and architecture of HCC.     

Multifocal nodular fatty infiltration of the liver mimicking metastatic disease on CT: imaging findings and diagnosis using MR imaging

The aim of this study was to describe the MR appearance of multifocal nodular fatty infiltration of the liver (MNFIL) using T1-weighted in-phase (IP) and opposed-phase (OP) gradient-echo as well as T2-weighted turbo-spin-echo sequences with fat suppression (FSTSE) and without (HASTE). Magnetic resonance imaging examinations at 1.5 T using T1-weighted IP and OP-GRE with fast low angle shot (FLASH) technique, and T2-weighted FSTSE, T2-weighted HASTE of 137 patients undergoing evaluation for focal liver lesions were reviewed. Five patients were identified in whom CT indicated metastatic disease; however, no liver malignancy was finally proven. Diagnosis was confirmed by biopsy (n = 3), additional wedge resection (n = 1) or follow-up MRI 6–12 months later (n = 5). Regarding the identified five patients, the number of focal liver lesions was 2 (n = 2) and more than 20 (n = 3). The MR imaging characteristics were as follows: OP-image: markedly hypointense (n = 5); IP image: isointense (n = 2) or slightly hyperintense (n = 3); T2-weighted FSTSE-image: isointense (n = 5); T2-weighted HASTE image isointense (n = 1); slightly hyperintense (n = 4). On OP images all lesions were sharply demarcated and of almost spherical configuration (n = 5). Further evaluation by histology or follow-up MR imaging did not give evidence of malignancy in any case. Histology revealed fatty infiltration of the liver parenchyma in three patients. Magnetic resonance follow-up showed complete resolution in two patients and no change in three patients. Multifocal nodular fatty infiltration can simulate metastatic disease on both CT and MR imaging. The combination of in-phase (IP) and opposed-phase (OP) gradient-echo imaging can reliably differentiate MNFIL from metastatic disease. Received: 15 September 1999 Revised: 3 February 2000; Accepted: 7 February 2000     

Sclerosed liver hemangioma mimicking malignant tumor at MR imaging: Pathologic correlation

This case report illustrates atypical magnetic resonance (MR) imaging findings in a liver hemangioma mimicking a malignant lesion—lower signal intensity than cerebrospinal fluid on T2-weighted spin-echo images and lack of early enhancement on dynamic contrast material—enhanced gradient-echo images. Pathologic analysis demonstrated nearly total replacement of the vascular cavities by dense fibrous tissue. In this rare, sclerosed form, this lesion could not be defined as a hemangioma with MR imaging.     

Benign and malignant hepatocellular tumors: evaluation of tumoral enhancement after mangafodipir trisodium injection on MR imaging

The aim of this work was to study the ability of mangafodipir trisodium (Mn-DPDP)-enhanced MR imaging in differentiating malignant from benign hepatocellular tumors. Eleven patients with pathologically proved hepatocellular carcinomas, six with focal nodular hyperplasias, and one with a single hepatocellular adenoma were examined by spin-echo and gradient-echo T1-weighted sequences before, 1 h after, and 24 h after intravenous injection of Mn-DPDP (5 μmol/kg). Quantitative analysis including enhancement and lesion-to-liver contrast-to-noise ratio, and qualitative analysis including the presence of a central area and a capsule were done on pre- and post-Mn-DPDP-enhanced images. Enhancement was observed in all the tumors with significant improvement (p < 0.05) in contrast-to-noise ratio 1 h after, and 24 h after intravenous injection of Mn-DPDP. There were no significant differences in the mean enhancement and the mean contrast-to-noise ratio (CNR) between benign and malignant tumors. No enhancement was seen within internal areas observed in 7 hepatocellular carcinomas, and in 5 focal nodular hyperplasias, and within capsules which were observed in 9 hepatocellular carcinomas. In our study, Mn-DPDP increased CNR of both benign and malignant tumors but did not enable differentiation between benign and malignant tumors of hepatocellular nature. Received: 7 October 1997; Revision received: 25 February 1998; Accepted: 10 July 1998     

CT and MR imaging findings of xanthogranulomatous cholecystitis: correlation with pathologic findings

The aim of this study was to evaluate CT and MRI findings in xanthogranulomatous cholecystitis (XGC) and to correlate the imaging findings with various pathologic parameters. The study included 13 patients with histopathologically confirmed XGC. The CT (n=13) and MRI (n=5) obtained in these patients were evaluated retrospectively. On CT, low-attenuation areas in the wall of XGC correlated with foam and inflammatory cells or necrosis and/or abscess in XGC. Areas of iso- to slightly high signal intensity on T2-weighted images, showing slight enhancement at early phase and strong enhancement at last phase on dynamic study, corresponded with areas of abundant xanthogranulomas. Areas with very high signal intensity on T2-weighted images without enhancement corresponded with necrosis and/or abscesses. Luminal surface enhancement (LSE) of gallbladder wall represented preservation of the epithelial layer. The early-enhanced areas of the liver bed on dynamic CT and MR images corresponded with accumulation of inflammatory cells and abundant fibrosis. Our results indicate that CT and MRI findings correlate well with the histopathologic findings of XGC.     

Occlusive and reperfused myocardial infarcts: differentiation with Mn- DPDP--enhanced MR imaging

To assess whether the administration of manganese N,N'-bis(pyridoxal-5-phosphate)ethylenediamine-N,N'-diacetic acid (DPDP) permits differentiation between occlusive and reperfused infarcts, the authors subjected rats to either 6 hours of left coronary artery occlusion (n = 13) or 2 hours of occlusion followed by 4 hours of reperfusion (n = 10) before magnetic resonance (MR) imaging. Electrocardiographic-gated T1-weighted images were obtained before and for 1 hour after injection of 400 mumol/kg of Mn-DPDP. On T1-weighted images obtained before injection of Mn-DPDP. no significant differences in signal intensity were observed between normal and infarcted regions. Use of Mn-DPDP permitted delineation of the area of infarction. The pattern of enhancement in the injured zone was different for occlusive and reperfused myocardial infarcts. In rats with occlusive infarcts, In rats with occlusive infarcts, three well-defined zones were seen. Epicardium and endocardium were enhanced, while the midmyocardial zone was hypointense. The midmyocardial signal intensity gradually increased during the 60 minutes after injection. In rats with reperfused infarcts, the injured area was uniformly and intensely enhanced. Histologic examination confirmed the presence and location of myocardial infarct. Mn-DPDP may improve the detection and delineation of acute myocardial infarcts, demonstrate perfusion of the infarct, and permit discrimination between reperfused and occlusive infarcts.