Assessment of acute myocardial infarction in man with magnetic resonance imaging and the use of a new paramagnetic contrast agent gadolinium-bopta

To assess the feasibility of and characterize the new paramagnetic contrast agent gadolinium-BOPTA/dimeglumine (Gd-BOPTA) to detect acute myocardial infarctions with MR imaging, 24 patients (53.3 ± 8.3 yr) were examined 9.3 ± 3.6 days after a first myocardial infarction. Short-axis T₁-weighted and T₂-weighted MR imaging was performed at three slice levels. T₁-weighted images were obtained before, immediately after, 15, 30, and 45 min after injection. Patients received either 0.05 or 0.1 mmol/kg body weight Gd-BOPTA. Images were qualitatively and quantitatively analyzed. Two patients showed no signs of infarction on T₂-weighted images as opposed to contrast-enhanced T₁-weighted images. Contrast-to-noise ratio was not affected by the dosage level. Signal intensity (SI) of normal to infarcted myocardium was significantly improved by both dosages (p < .0005) but a dosage of 0.05 mmol/kg produced significantly higher SI inf/norm (1.42 ± 0.07 vs. 1.34 ± 0.06, respectively, p = .015). SI of normal and infarcted myocardium enhanced immediately after administration of 0.05 mmol/kg (29.3 ± 5.1% and 53.8 ± 9.6% respectively), which decreased thereafter to 5.3 ± 4.8% and 40.2 ± 8.5% respectively, at 45 min (p < .002 for normal myocardium). SI enhancement immediately after 0.1 mmol/kg Gd-BOPTA showed no decrease within the first 45 min. Gd-BOPTA enables the detection of myocardial infarction. Optimal infarct delineation is achieved from 15 to 45 min after administration of 0.05 mmol/kg body weight Gd-BOPTA. Gd-BOPTA at 0.05 mmol/kg does improve image quality as measured by contrast-to-noise ratio and SI enhancement as compared to 0.10 mmol/kg.     

Magnetic resonance imaging dynamic contrast enhancement (DCE) characteristics of healed myocardial infarction differ from viable myocardium

Purpose

To determine whether healed myocardial infarction alters dynamic contrast-enhancement (DCE) curve shapes as well as late gadolinium-enhancement (LGE).

Materials and methods

Twenty patients with chronic myocardial infarction underwent MR imaging at 1.5 T with blood and myocardial T1 measurements before and after contrast administration for forty minutes. Viable and infarcted myocardial partition coefficients were calculated using multipoint slope methods for ten different DCE sampling intervals and windows. Partition coefficients and coefficients of determination were compared with paired statistical tests to assess the linearity of DCE curve shapes over the 40 min time period.

Results

Calculated partition coefficients did not vary significantly between methods (p = 0.325) for viable myocardium but did differ for infarcted myocardium (p < 0.001), indicating a difference in infarcted DCE. There was a significant difference between viable and infarcted myocardial partition coefficients estimates for all methods with the exception of methods that included measurements during the first 10 min after contrast agent administration.

Conclusion

Myocardial partition coefficients calculated from a slope calculation vary in healed myocardial infarction based on the selection of samples due to non-linear DCE curve shapes. Partition coefficient calculations are insensitive to data sampling effects in viable myocardium due to linear DCE curve shapes.     

Inflammatory imaging with ultrasmall superparamagnetic iron oxide

The purpose of this study was to investigate the usefulness and feasibility of magnetic resonance imaging (MRI) with ultrasmall superparamagnetic iron oxide (USPIO) (USPIO-enhanced MRI) for imaging inflammatory tissues. First, we investigated the relationship between the apparent transverse relaxation rate (R2*) and the concentration of USPIO by phantom studies and measured the apparent transverse relaxivity (r2*) of USPIO. Second, we performed animal experiments using a total of 30 mice. The mice were divided into five groups [A (n=6), B (n=6), C (n=6), sham control (n=6), and control (n=6)]. The mice in Groups A, B, C and control were subcutaneously injected with 0.1 ml of turpentine oil on Day 0, while those in the sham control group were subcutaneously injected with 0.1 ml of saline. The mice in Groups A, B, C and sham control were intraperitoneally injected with 200 μmol Fe per kilogram body weight of USPIO (28 nm in diameter) immediately after the first MRI study on Days 3, 5, 7 and 7, respectively, and those in the control group were not injected with USPIO. The second and third MRI studies were performed at 24 and 48 h after USPIO administration, respectively. The maps of R2* were generated from the apparent transverse relaxation time (T2*)-weighted images with six different echo times. The phantom studies showed that there was a linear relationship between R2* and the concentration of USPIO (r=0.99) and the r2* value of USPIO was 105.7 mM⁻¹ s⁻¹. There was a significant increase of R2* in inflammatory tissues in Group C at 24 h after USPIO administration compared with the precontrast R2* value. Our results suggest that USPIO-enhanced MRI combined with R2* measurement is useful for detecting inflammatory tissues.     

Magnetic resonance imaging in patients with unstable angina: comparison with acute myocardial infarction and normals

The role of magnetic resonance imaging in characterizing normal, ischemic and infarcted segments of myocardium was examined in 8 patients with unstable angina, 11 patients with acute myocardial infarction, and 7 patients with stable angina. Eleven normal volunteers were imaged for comparison. Myocardial segments in short axis magnetic resonance images were classified as normal or abnormal on the basis of perfusion changes observed in thallium-201 images in 22 patients and according to the electrocariographic localization of infarction in 4 patients. T2 relaxation time was measured in 57 myocardial segments with abnormal perfusion (24 with reversible and 33 with irreversible perfusion changes) and in 25 normally perfused segments. T2 measurements in normally perfused segments of patients with acute myocardial infarction, unstable angina and stable angina were within normal range derived from T2 measurements in 48 myocardial segments of 11 normal volunteers (42 +/- 10 ms). T2 in abnormal myocardial segments of patients with stable angina also was not significantly different from normal. T2 of abnormal segments in patients with unstable angina (64 +/- 14 in reversibly ischemic and 67 +/- 21 in the irreversibly ischemic segments) was prolonged when compared to normal (p less than 0.0001) and was not significantly different from T2 in abnormal segments of patients with acute myocardial infarction (62 +/- 18 for reversibly and 66 +/- 11 for irreversibly ischemic segments). The data indicate that T2 prolongation is not specific for acute myocardial infarction and may be observed in abnormally perfused segments of patients with unstable angina.(ABSTRACT TRUNCATED AT 250 WORDS)     

Serial magnetic resonance imaging in patients following acute myocardial infarction.

The detection of serial changes in magnetic resonance (MR) signal intensity of the heart following acute myocardial infarction may provide a useful method of characterizing tissue healing. Fourteen patients with acute Q-wave infarction underwent T2-weighted, spin-echo cardiac imaging during hospitalization, followed by one or more additional MR studies (total 31) over a 6- to 27-wk period (mean: 3 mo). Visual assessment of the images demonstrated a gradual reduction in signal intensity and localization of the bright signal to the subendocardium of the infarction region over the three-mo study period. A quantitative measurement of signal intensity (infarction/normal myocardium) fell from 1.81 +/- 0.42 on the initial study to 1.34 +/- 0.37 (p less than 0.05) at a mean of 14 wk. Two patients had an increase in signal intensity on the follow-up study and both patients had been readmitted with acute coronary syndromes. In summary, characterization of changes in signal intensity may provide a useful method of assessing myocardial healing following acute myocardial infarction. Further studies are indicated to determine the prognostic significance of these parameters.     

Magnetic resonance imaging with superparamagnetic iron oxide particles for the detection of myocardial reperfusion

The effect of superparamagnetic iron oxide particles on magnetic resonance myocardial signal intensity was examined in order to define the ability of this agent to identify normal, ischemic, and reperfused myocardium. Data were obtained from 6 normal rats (group 1) and from 6 heterotopic isogenic rat heart transplants (group 2) at 4.7 T with a multislice spin-echo sequence. Images were acquired in (a) normal rats before and after the infusion of 36 μmol Fe/kg of AMI-25 (group 1) and (b) rat heart transplants during control, global myocardial ischemia (before and after the injection of 72 μmol Fe/kg of AMI-25), and following reperfusion (group 2). Myocardial signal intensity decreased by 36 ± 4%, p < 0.001, following contrast infusion in normal hearts (group 1). The intensity remained constant in the rat heart transplants (group 2) during coronary occlusion, both before and after the infusion of AMI-25 and decreased by 61 ± 7%, p < 0.001, upon reperfusion. The larger effect of AMI-25 in reperfused as compared to normal myocardium suggests the presence of ischemia-induced hyperemia. There was no significant difference (analysis of variance) among intensities from different myocardial regions in either group at any stage of the experiment. We conclude that the use of AMI-25 permits identification of normal, ischemic, and reperfused myocardium and may therefore be helpful for the early detection of reperfusion following thrombolytic therapy for acute myocardial infarction.     

Effect of hyperosmotic mannitol on magnetic resonance relaxation parameters in reperfused canine myocardial infarction

To determine how administration of a hyperosmotic agent alters regional nuclear magnetic resonance (NMR) relaxation parameters and imaging characteristics in ischemic-reperfused myocardium, 7 dogs were infused with mannitol for 15 minutes before and after the release of a 3 hour left anterior descending coronary artery (LAD) occlusion. Nine control animals received normal saline during the 3 hour occlusion and 1 hour reperfusion periods. Normal posterior left ventricular (LV) wall and the ischemic anterior LV wall (risk area) myocardium was sampled for calculation of segmental microsphere myocardial blood flow, % tissue water content, NMR relaxation times (T1, T2) and myocyte ultrastructure using electron microscopy. Mean infarct T1 values were 14% greater than normal segments in saline-treated controls, but only 5% greater after mannitol. The difference in tissue water content between infarcted and normal segments was 4% in saline-treated (83 vs. 79%) compared to 2% in mannitol-treated dogs (79 vs. 77%). T1, T2 and % water content of control infarct segments were greater than treated infarcts (p less than 0.01). T1 and T2 rose as occlusion flow fell below 0.5 ml/min/g in control hearts but did not rise until flows were reduced to 0.1 ml/min/g in mannitol-treated hearts. Areas of increased signal in T1 and T2 NMR images correlated well with histochemical infarct volume (r = 0.98, SEE = 1.1 cc) in mannitol-treated dogs, but infarct borders were qualitatively less well-defined than in controls. We concluded that mannitol (1) diminishes tissue edema and reduces NMR relaxation parameters (T1, T2) in infarcted myocardium; and (2) attenuates the rise in T1 and T2 and ultrastructural myocyte injury in ischemic-reperfused myocardium.     

Investigation of atherosclerotic plaques with MRI at 3 T using ultrasmall superparamagnetic particles of iron oxide

This study aims to investigate the uptake of the experimental ultrasmall superparamagnetic particles of iron oxide (USPIO) contrast agent DDM43/34 (Schering AG, Berlin, Germany) by aortic atherosclerotic plaques using magnetic resonance imaging (MRI) at 3 T. Six Watanabe heritable hyperlipidemic rabbits were injected with USPIO at doses of 0.1–1.0 mmol/kg Fe. Parasagittal magnetic resonance angiography (MRA) scans were acquired using 3D gradient-echo sequences before and after USPIO administration, then again after 6 h, 1 day, 2 days and 5 days. At later time points, when the USPIO concentration was too low to enhance blood signal, additional MRA scans were acquired during the infusion of gadopentate dimeglumine (Magnevist; Schering AG). In the images, widespread susceptibility artifacts demonstrated readily detectable USPIO uptake in the liver, bone marrow and lymphatic vessels. Surprisingly, however, no such effects could be associated specifically with the aortic vessel wall, in contrast to previous studies that showed strong uptake with similar pulse sequences. Histological analysis was performed on aortic slices from two animals, demonstrating that aortic plaques were active but showed very little USPIO uptake, consistent with MRI findings. We conclude that, despite the exciting potential of plaque detection using USPIO, some caution is advised since the absence of susceptibility effects does not necessarily imply the absence of plaque, even at 3 T, which offers increased sensitivity to susceptibility. Future work will investigate the dependence of such results on stage of plaque development, magnetic field strength and choice of contrast agent.     

USPIO-Enhanced MR imaging of glycerol-induced acute renal failure in the rabbit

Enhanced-MR imaging in combination with ultrasmall superparamagnetic iron oxide (USPIO) was used in the glycerol-induced model of acute renal failure (ARF) in the rabbit to detect renal perfusion abnormalities. A control group (n = 5) and an ARF group (n = 5) were studied after intramuscular injection of glycerol (10 ml/kg) with T₂-weighted spin-echo sequence at 1.5 T and a 27 μmol/kg IV dose of iron. The signal intensity (SI) was quantified in the cortex, the outer medulla (OM), and the inner medulla (IM). In control rabbits, the maximum SI decrease after USPIO injection was in the OM (76% ± 3.6), as this is the region of maximal vascular density, then in the IM (73.4% ± 2.9). In the glycerol group, SI loss in the OM (61% ± 12.6) and the IM (45.2% ± 16.24) was significant less than in the control group (p < .05). Pathology results showed fibrinous thrombus in the efferent arterioles and congestive aspect of the vasa recta in the medulla. We argue that a reduced medullary concentration of USPIO in the renal failure group is indicative of medullary hypoperfusion.     

Detection of toxoplasmic lesions in mouse brain by USPIO-enhanced magnetic resonance imaging

The objective of this study was to examine the feasibility of detecting toxoplasmic brain lesions in a mouse model of cerebral toxoplasmosis by ultrasmall superparamagnetic particles of iron oxide (USPIO)-enhanced magnetic resonance imaging (MRI). Toxoplasmosis encephalitis was induced in Kunming mice by intracerebral injection of Toxoplasma gondii tachyzoites. T₂- and T₂*-weighted MRI was performed 1, 3, 4, 5 and 6 days after infection before USPIO injection; immediately after USPIO injection; and 24 h later. A comparison of USPIO enhancement and Gd-DTPA enhancement was made in three toxoplasmic mice 4 days after infection. Hematoxylin and eosin staining and Prussian blue staining were performed to detect inflammatory reactions and presence of iron in and around the toxoplasmic brain lesions. Nonenhanced T₂-/T₂*-weighted imaging detected few abnormalities in the brain up to 5 days. Most mice developed prominent hydrocephalus at 6 days. Gd-DTPA-enhanced imaging showed prominent enhancement of the cerebral ventricles but revealed only few space-occupying lesions in the parenchyma. USPIO-enhanced T₂*-weighted imaging showed improved detection of toxoplasmic brain lesions that were invisible to nonenhanced T₂-/T₂*-weighted imaging and gadolinium-enhanced imaging. Most of the enhancing lesions showed nodular enhancement immediately after USPIO injection, some of which changed appearance 24 h later, having a ring enhancement at the outer rim. It can be concluded that USPIO enhancement of the toxoplasmic lesions may reflect blood–brain barrier impairment and/or inflammatory reactions associated with these lesions. USPIO-enhanced imaging may be used in combination with gadolinium-enhanced imaging to provide better characterization of toxoplasmic brain lesions and, potentially, improve the differential diagnosis of toxoplasmosis encephalitis.     

Extra- and intracellular accumulation of ultrasmall superparamagnetic iron oxides (USPIO) in experimentally induced abscesses of the peripheral soft tissues and their effects on magnetic resonance imaging

The effects of ultrasmall superparamagnetic iron oxide (USPIO) particles on magnetic resonance imaging (MRI) were studied in an animal abscess model and the findings compared with microscopic sections of the abscesses. Staphylogenic abscesses of the right hind leg were induced in six Sprague-Dawley rats. The USPIO particles consisted of polyethylene-glycol-coated Fe3O4 with a mean size of 26 nm and were injected intravenously (i.v.), with three animals receiving a dose of 50 micromol/kg and three animals a dose of 150 micromol/kg. Before and immediately after i.v. administration of the particles, MR data were acquired with fast gradient-echo technique FLASH sequences applied over a period of 60 min. The Fe3O4-induced signal changes were registered in regions of interest (ROIs) placed over the margin and center of the abscess, over the perifocal granulation tissue and over corresponding sites of the contralateral healthy muscle. Microscopic sections were prepared using the conventional paraffin technique and, in part, a kryohistologic method before staining of the specimen with hematoxylin and Berlin-blue reaction. In addition to the mostly perfusion dependent loss of signal intensity within 8 s after injection, a signal reduction, which could be rather pronounced, was observed in the abscess margin and perifocal granulation tissue, with the underlying mechanism mainly attributed to extravasation and predominantly extracellular deposition of Fe3O4. CONCLUSION: The USPIO particles used in this study lead to a prolonged demarcation of abscesses in the peripheral soft tissues due to particle extravasation and accumulation in the periphery of the abscesses. Besides the known accumulation of already characterized USPIO in the RES of liver, spleen and lymph nodes the study could demonstrate ultrasmall iron oxide deposition (BY 818) in abscesses of the peripheral soft tissue.     

MR imaging of murine arthritis using ultrasmall superparamagnetic iron oxide particles.

The objective of this work was to determine the ability of magnetic resonance (MR) imaging with ultrasmall superparamagnetic iron oxide (USPIO) particles to provide quantitative measures of inflammation in autoimmune arthritis.Mice were injected intravenously or intra-articularly with USPIO followed by magnetic resonance and histological assessment of the knee joint. Comparisons were made between MR microimages and histology in na?ve mice and mice with collagen-induced arthritis.Following intravenous administration, accumulation of USPIO was observed in the popliteal lymph nodes, but not the joint. Administration of USPIO intra-articularly resulted in signal loss in the joint. The MR signal intensity could be quantified and correlated with iron staining in the synovial lining. A marked increase in USPIO uptake and a corresponding decrease in signal intensity were observed in arthritic, compared to na?ve mice. Areas of focal signal loss corresponded to foci of iron staining by histology.These studies may provide a basis for the clinical application of USPIO in arthritis for assessing disease severity and monitoring response to therapy.     

Influence of the hepatobiliary contrast agent mangafodipir trisodium (Mn-DPDP) on the imaging properties of abdominal organs

To assess the influence of Mangafodipir Trisodium on the imaging properties of abdominal organs when using T₁-weighted gradient-echo (GE) and T₂-weighted turbo spin-echo (TSE) sequences, thirty patients with focal lesions in the liver were examined at a field strength of 1.5 T before and after intravenous administration of Mangafodipir Trisodium (dose: 5 μmol/kg of body weight).Administration of Mangafodipir Trisodium led to a significant increase in the signal intensity of the liver tissue (p < 0.001), the spleen (p < 0.01), the pancreas (p < 0.001), and the kidneys (p < 0.001) in the T₁-weighted GE sequence, while there was no relevant enhancement in fatty tissue and the musculature. In the T₂-weighted turbo spin-echo sequence, there was no relevant change in the signal following administration of a contrast agent. The contrast-to-noise ratio (C/N) between the lesions and the liver tissue increased significantly in the post-contrast T₁-weighted GE sequence (p < 0.001), while there was no change in the contrast-to-noise ratio in the post-contrast T₂-weighted turbo spin-echo sequence. The contrast-to-noise ratio of the plain T₂-weighted TSE sequence was significantly higher than that in the post-contrast T₁-weighted GE sequence (p < 0.001). Although Mangafodipir Trisodium was primarily developed as a hepatobiliary contrast agent for demonstration and differentiation of liver lesions, it also affects the signal levels in the pancreas, spleen, and kidneys in the T₁-weighted image. Awareness of this effect on the extrahepatic tissue makes it easier to interpret pathological findings in magnetic resonance imaging (MRI) of the abdomen.     

Functional magnetic resonance imaging of human renal allografts during the post-transplant period: Preliminary observations

Graft dysfunction is a common occurrence during the first weeks following renal transplantation. The current study was designed to evaluate the potential of renal magnetic resonance (MR) perfusion imaging to differentiate acute allograft rejection (AAR) from acute tubular necrosis (ATN) during the post-transplant period. Twenty-three consecutive patients with clinically suspected ATN and/or AAR and eight consecutive control patients (asymptomatic, serum creatinine concentration < 1.5 mg/dL) underwent MR perfusion imaging of the renal allograft within 64 days after transplantation. Histopathology was obtained in all cases with clinical suspicion of ATN or AAR. Sixty sequential fast gradient-recalled-echo MR images were acquired in each patient after intravenous administration of gadolinium-DTPA (0.1 mmol/kg). Histopathology revealed 6 patients with pure AAR, 4 patients with a combination of AAR and ATN, 12 patients with ATN and 1 patient with normal findings. Kidney graft recipients with normal renal function showed a moderate increase in signal intensity (SI) of the renal cortex and medulla after administration of contrast agent followed by an immediate and short decrease in SI of the medulla (biphasic medullary enhancement pattern). The increase in cortical SI of patients with AAR was significantly smaller (61 ± 4% increase above baseline) than that measured in normal allografts (136 ± 9% increase above baseline) (p < 0.05) and patients with ATN (129 ± 3% increase above baseline) (p < .05). Patients with ATN had a slightly delayed and diminished cortical enhancement and an uniphasic and lesser medullary enhancement pattern compared to that observed in normal allografts (p < 0.05). A close correlation (r = 0.72) was found between serum creatinine concentration levels and changes in SI. Thus, MR imaging results and histopathology were in agreement in 22 of 23 patients (96%). MR perfusion imaging of renal allografts can be used to noninvasively differentiate ATN from AAR during the post-transplant period, and may also be helpful in cases where covert AAR is superimposing ATN during a phase of anuria. Patients with ATN can be separated from normals in the majority of cases as reflected by an uniphasic medullary enhancement pattern.     

Intraventricular dispersion and temporal delay of early left ventricular filling after acute myocardial infarction. Assessment by magnetic resonance velocity mapping

This article aims to describe early left ventricular diastolic inflow using magnetic resonance velocity mapping in patients with recent acute myocardial infarction and in normal volunteers. Magnetic resonance velocity mapping was performed in a long axis plane through the hearts of 46 patients with recent, first time acute myocardial infarction and 43 age-matched normal volunteers. The peak velocities at six levels of the early diastolic inflow stream were recorded. A velocity index was calculated as the peak velocity in each position relative to the peak velocity at the mitral leaflet tips. Also, the temporal delay of velocity propagation was computed. Velocity index 4 cm downstream of mitral leaflet tips was lower in the acute myocardial infarction group (0.42 (0.17)) (mean (SD)) compared to controls (0.59 (0.25)) (p < 0.001). Temporal delay in the same position was longer in the acute myocardial infarction group (62 (67) ms) than in controls (32 (39) ms) (p < 0.02). Blood flow patterns in patients after acute myocardial infarction were characterized by increased dispersion of velocities and increased temporal delay of velocity propagation, probably reflecting impaired active left ventricular relaxation. Intraventricular flow measurements constitute a promising new technique for non-invasive assessment of left ventricular diastolic function.     

Quantification of myocardial viability distribution with Gd(DTPA) bolus-enhanced, signal intensity-based percent infarct mapping

Introduction

A substantial, common shortcoming of the currently used semiautomated techniques for the quantification of myocardial infarct with delayed enhancement magnetic resonance imaging is the assumption that the whole myocardial slab that corresponds to the hyperenhanced tomographic area is 100% nonviable. This assumption is, however, incorrect. To resolve this conflict, we have recently proposed the signal intensity percent-infarct mapping method and validated it in an ex vivo, canine experiment. The purpose of the current study has been the validation of the signal intensity percent-infarct mapping method in vivo, using a porcine model of reperfused myocardial infarct.

Methods

In swines (n=6), reperfused myocardial infarct was generated occluding for 90 min by an angioplasty balloon either the left anterior descending or the left circumflex coronary artery. To obtain DE images, Gd(DTPA) enhanced inversion-recovery fast gradient-echo acquisitions were carried out on day 28 after myocardial infarction. Scanning started 15 min after intravenous injection of 0.2 mmol/kg Gd(DTPA). At the end of the MRI session, the animal was sacrificed and 2,3,5-triphenyltetrazolium chloride staining was used to validate the existence and to determine the accurate size of the myocardial infarct. Tissue samples were taken and stained with hematoxylin-eosin and Masson's trichrome for histological assessment of the infarct and the periinfarct zone. The signal intensity percent-infarct mapping data were compared with corresponding data from the delayed enhancement images analyzed with SI_remote+2S.D. thresholding, and with corresponding triphenyltetrazolium-chloride staining data using Friedman's repeated measure analysis of variance on ranks.

Results

The infarct volume determined by the triphenyltetrazolium chloride, SI_remote+2S.D. and signal intensity percent-infarct mapping methods was 3.04 ml [2.74, 3.45], 13.62 ml [9.06, 18.45] and 4.27 ml [3.45, 6.33], respectively. Median infarct volume determined by SI_remote+2S.D. significantly differed from that determined by triphenyltetrazolium chloride (P<.05). The Bland-Altman overall bias was 12.49% of the volume of the left ventricle. Median infarct volume determined by signal intensity percent-infarct mapping, however, did not differ significantly (NS) from that obtained by triphenyltetrazolium chloride. Signal intensity percent-infarct mapping yielded only a 1.99% Bland-Altman overall bias of the left ventricular volume.

Conclusions

This in vivo study in the porcine reperfused myocardial infarct model demonstrates that signal intensity percent-infarct mapping is a highly accurate method for the determination of the extent of myocardial infarct. MRI images for signal intensity percent-infarct mapping are obtained with the pulse sequence of conventional delayed enhancement imaging and are acquired within clinically acceptable scanning time. This makes signal intensity percent-infarct mapping a practical method for clinical implementation.     

Three-dimensional (13)C-spectroscopic imaging in the isolated infarcted rat heart

Acquisition weighted (13)C-spectroscopic imaging with three spatial dimensions is demonstrated in the isolated, perfused rat heart. Experiments were performed at 11.75 T with a home-built double resonant (13)C-(1)H probehead. Three-dimensional chemical shift imaging was used to obtain (1)H-decoupled (13)C-spectra in 96-microl voxels in about 58 min. Acquisition weighting significantly reduced signal contamination and improved image quality, with no penalty in sensitivity. As a first application, infarcted hearts were studied during perfusion with [2-(13)C]-sodium acetate. The extent of the incorporation of the (13)C-label into glutamate allows us to distinguish intact and infarcted myocardium. Chemical shift images show a homogeneous glutamate distribution in intact tissue, but a negligible amount in the infarction scar.     

Left ventricular aneurysmectomy after myocardial infarction following detection of left ventricular thrombosis by magnetic resonance imaging

A 54-year-old man with a history of myocardial infarction presented with recurrent transient ischemic attacks 7 yr after the acute event. The emboli originated from a left ventricular thrombus despite adequate oral anticoagulant therapy. The thrombus was best detected with magnetic resonance imaging and had to be removed by surgery.     

Quantitative assessment of regional systolic and diastolic functions and temporal heterogeneity of myocardial contraction in patients with myocardial infarction using cine magnetic resonance imaging and Fourier fitting

Purpose

The objective of this study is to determine regional left ventricle (LV) function and temporal heterogeneity of LV wall contraction by analyzing regional time–volume curve (TVC) after Fourier fitting and to assess altered systolic and diastolic functions and temporal indices of myocardial contraction in infarcted segments in comparison with noninfarcted myocardium in patients with myocardial infarction (MI).

Methods

Steady-state cine magnetic resonance (MR) and late gadolinium-enhanced (LGE) MR images were acquired using a 1.5-T MR system in 60 patients with MI. Regional LV function was determined by analyzing regional TVC in 16 segments. The fitted regional TVC was generated by Fourier curve fitting with five harmonics. Regional LV ejection fraction (EF), peak ejection rate (PER), peak filling rate (PFR), time to end-systole and time to peak filling (TPF) were determined from TVC and the first derivative curve.

Results

On LGE MR imaging (MRI), MI was observed in 307 of 960 segments (32.0%). Regional EF and PER averaged in LGE segments were 49.3±14.5% and 2.83±0.65 end-diastolic volume (EDV)/s, significantly lower than those in normal segments (66.7±11.9% and 3.63±0.60 EDV/s, P<.001 and P<.01, respectively). In addition, regional PFR, an index of diastolic function, was significantly reduced in LGE segments (1.94±0.54 vs. 2.86±0.68 EDV/s, P<.01). Time to end-systole and TPF were significantly greater in LGE segments (380.2±57.6 and 169.3±45.4 ms) than in normal segments (300.9±55.1 and 132.3±43.0 ms, P<.01 and P<.01, respectively).

Conclusions

Analysis of regional TVC on cine MRI after Fourier fitting allows quantitative assessment of regional systolic and diastolic LV functions and temporal heterogeneity of LV wall contraction in patients with MI.     

MR imaging of non-cancerous hepatic lesions in Long-Evans Cinnamon rats

We measured MR images of the liver of Long-Evans Cinnamon (LEC) rats with pathologic correlation and assessed the effectiveness of MR imaging (MRI) for diagnosis of noncancerous hepatic lesions. T₁- and T₂-weighted images of their livers were obtained, and the dynamic and delayed studies after intravenous gadolinium injection were also performed. Cholangiofibrosis showed low signal intensity on T₁-weighted images and high signal intensity on T₂-weighted images. The T₂ relaxation time of cholangiofibrosis was significantly prolonged (p < .01), and the signal intensity ratio of this lesion to muscle on T₁-weighted images was significantly lower than that of normal liver parenchyma to muscle (p < .01). The lesion was enhanced immediately after gadolinium injection and the enhancement was prolonged. Among three cases of peliosis hepatis identified, one showed heterogeneous intensities on both T₁- and T₂-weighted images and the other two showed similar intensity pattern to cholangiofibrosis. The characteristic MR appearance of cholangiofibrosis may be useful to distinguish it from hepatocellular carcinoma (HCC).