Magnetic Resonance Imaging of Myocardial Perfusion and Viability Using a Blood Pool Contrast Agent

Visualization of chronic myocardial infarction using the intravascular contrast agent MS-325 (gadofosveset) in patients

Aims. The aim of this study was to evaluate the potential of visualizing chronic myocardial infarction in patients using the intravascular CA MS-325 (gadofosveset, EPIX Pharmaceuticals, Mass, USA). Methods. Nine patients were enrolled in a clinical phase II multicenter trial for MRCA and perfusion imaging using MS-325. They had objective evidence of chronic myocardial infarction as visualized by previously performed late gadolinium (Gd) enhancement imaging (LGE) with a conventional extracellular Gd-DTPA CA (Magnevist, Bayer Healthcare, Germany, 0.2 mmol/kg/body weight) serving as reference standard. A prepulse-optimized LGE study was performed immediately and at several time points after injection of MS-325 (0.05 mmol/kg/body weight). The number and localization of segments demonstrating LGE with MS-325 as well as signal intensities were compared with the reference standard (Gd-DTPA). Results. Using MS-325, LGE could be detected at every time point in all 9 patients. The accuracy of LGE with MS-325 as compared to LGE with Gd-DTPA was highest 54 ± 4 minutes after contrast injection, resulting in a sensitivity of 84% with a specificity of 98%. Conclusion. The intravascular CA MS-325 has the potential to visualize chronic myocardial infarction. However, in comparison with Gd-DTPA, the transmural extent and the number of segments are smaller.

Comparison of intravascular and extracellular contrast media for absolute quantification of myocardial rest-perfusion using high-resolution MRI

PURPOSE

To use the contrast agent gadofosveset for absolute quantification of myocardial perfusion and compare it with gadobenate dimeglumine (Gd-BOPTA) using a high-resolution generalized autocalibrating partially parallel acquisition (GRAPPA) sequence.

MATERIALS AND METHODS

Ten healthy volunteers were examined twice at two different dates with a first-pass perfusion examination at rest using prebolus technique. We used a 1.5 T scanner and a 32 channel heart-array coil with a steady-state free precession (SSFP) true fast imaging with steady state precession (trueFISP) GRAPPA sequence (acceleration-factor 3). Manual delineation of the myocardial contours was performed and absolute quantification was performed after baseline and contamination correction. At the first appointment, 1cc/4cc of the extracellular contrast agent Gd-BOPTA were administered, on the second date, 1cc/4cc of the blood pool contrast agent (CA) gadofosveset. At each date the examination was repeated after a 15-minute time interval.

RESULTS

Using gadofosveset perfusion the value (in cc/g/min) at rest was 0.66 ± 0.25 (mean ± standard deviation) for the first, and 0.55 ± 0.24 for the second CA application; for Gd-BOPTA it was 0.62 ± 0.25 and 0.45 ± 0.23. No significant difference was found between the acquired perfusion values. The apparent mean residence time in the myocardium was 23 seconds for gadofosveset and 19.5 seconds for Gd-BOPTA. Neither signal-to-noise ratio (SNR) nor subjectively rated image contrast showed a significant difference.

CONCLUSION

The application of gadofosveset for an absolute quantification of myocardial perfusion is possible. Yet the acquired perfusion values show no significant differences to those determined with Gd-BOPTA, maintained the same SNR and comparable perfusion values, and did not picture the expected concentration time-course for an intravasal CA in the first pass.

Assessment of the coronary venous system in heart failure patients by blood pool agent enhanced whole-heart MRI

OBJECTIVE

To investigate the feasibility of MRI for non-invasive assessment of the coronary sinus (CS) and the number and course of its major tributaries in heart failure patients.

METHODS

Fourteen non-ischaemic heart failure patients scheduled for cardiac resynchronisation therapy (CRT) underwent additional whole-heart coronary venography. MRI was performed 1 day before device implantation. The visibility, location and dimensions of the CS and its major tributaries were assessed and the number of potential implantation sites identified. The MRI results were validated by X-ray venography conventionally acquired during the device implantation procedure.

RESULTS

The right atrium (RA), CS and mid-cardiac vein (MCV) could be visualised in all patients. 36% of the identified candidate branches were located posterolaterally, 48% laterally and 16% anterolaterally. The average diameter of the CS was quantified as 9.8 mm, the posterior interventricular vein (PIV) 4.6 mm, posterolateral segments 3.3 mm, lateral 2.9 mm and anterolateral 2.9 mm. Concordance with X-ray in terms of number and location of candidate branches was given in most cases.

CONCLUSION

Contrast-enhanced MRI venography appears feasible for non-invasive pre-interventional assessment of the course of the CS and its major tributaries.

3D and 2D delayed-enhancement magnetic resonance imaging for detection of myocardial infarction: preclinical and clinical results

RATIONALE AND OBJECTIVES

The purpose was to verify whether myocardial viability can be detected by a delayed enhancement magnetic resonance imaging (MRI) approach using a rapid three-dimensional inversion-recovery fast low-angle shot (3D IR-FLASH) sequence in a preclinical and clinical setting.

MATERIALS AND METHODS

Nonreperfused myocardial infarctions were induced in eight minipigs. Both the pigs and 15 patients with suspected myocardial infarction underwent MRI using a rapid 3D IR-FLASH sequence and a two-dimensional IR-FLASH sequence as the reference standard.

RESULTS

In the pigs, a total of 52 segments with myocardial infarction were identified with both sequences and there was good agreement in transmurality of 99.5%. The infarction volume determined with the 3D IR-FLASH in the animal study (2.4 +/- 1.5 cm(3)) showed a good correlation with the histomorphometrically determined volume using triphenyltetrazolium chloride (2.3 +/- 1.2 cm(3), r = 0.98, P < .001) and the two-dimensional IR-FLASH sequence (2.3 +/- 1.4 cm(3), r = 0.99, P < .001). Eleven of 15 patients were found to have myocardial infarction in 37 myocardial segments with both sequences and there was a good agreement in transmurality of 98.8%. There was also a good correlation in the clinical study between the 3D and 2D sequences (6.9 +/- 6.7 cm(3) vs. 6.8 +/- 6.5 cm(3), r = 0.98, P < .001). In Bland-Altman analysis there was no significant under- or overestimation of the myocardial infarction volume using the 3D IR-FLASH sequence in comparison to the two-dimensional reference standard in both the preclinical and clinical study. The contrast-to-noise ratios were not significantly different between 3D and 2D sequences in the animal (34.7 +/- 1.5 vs. 33.8 +/- 2.6; P = .51) and clinical study (31.4 +/- 12.5 vs. 36.7 +/- 11.5; P = .31). The breathhold time for the 3D IR-FLASH sequence in the clinical study (20.4 +/- 2.2 s) was significantly shorter than that of the 2D IR-FLASH sequence (190.1 +/- 20.8 s, P < .001).

CONCLUSIONS

The rapid 3D IR-FLASH sequence detects myocardial infarction with high accuracy and allows a relevant reduction in acquisition time.

Improved Evaluation of Myocardial Perfusion and Viability With the Magnetic Resonance Blood Pool Contrast Agent P792 in a Nonreperfused Porcine Infarction Model

OBJECTIVES

To investigate whether a magnetic resonance (MR) blood pool contrast agent enables both evaluation of myocardial perfusion and viability in nonreperfused infarction in pigs.

MATERIALS AND METHODS

An optimized MR protocol using the blood pool contrast agent P792 (0.026 mmol/kg, twice the clinical dose, Guerbet, France) was investigated to evaluate nonreperfused myocardial infarction in an animal model. P792 was compared with the extracellular contrast agent Gd-DOTA (0.1 mmol/kg). The MRI findings were compared with histomorphometry performed with microspheres to evaluate perfusion and triphenyltetrazolium chloride (TTC) to evaluate viability. Contrast-enhanced MR imaging of the heart was performed on a 1.5-Tesla scanner 2 days after instrumentation in 6 minipigs. A saturation recovery steady-state free precession sequence was used for perfusion imaging and an inversion recovery fast low-angle shot sequence for evaluation of myocardial viability.

RESULTS

P792 tended to depict areas of reduced perfusion more accurately than Gd-DOTA (17.2% +/- 11.1% versus 13.7% +/- 8.0%) in comparison to the gold standard of histomorphometry with microspheres (18.2% +/- 9.8%). Moreover, P792, but not Gd-DOTA, depicted ischemic areas for 30 minutes after intravenous injection. The change in myocardial signal intensity during first pass was not significantly different after P792 compared with Gd-DOTA (140.3% +/- 64.4% versus 123.3% +/- 22.5%, P = 0.56). P792 was highly accurate in depicting infarcted areas (11.1% +/- 7.1%) compared with Gd-DOTA (12.1% +/- 8.2%, r = 0.98, P < 0.001) and histomorphometry with TTC (12.2% +/- 8.0%, r = 0.99, P < 0.001).

CONCLUSIONS

Unlike Gd-DOTA, the blood pool contrast agent P792 allows evaluation of myocardial perfusion for a period of 30 minutes and shows good agreement with histomorphometry. P792 must be examined in further studies to evaluate its potential in evaluating early myocardial lesions and reperfusion. In addition, P792 also allows for evaluation of myocardial viability.

Discrimination of Myocardial Acute and Chronic (Scar) Infarctions on Delayed Contrast Enhanced Magnetic Resonance Imaging With Intravascular Magnetic Resonance Contrast Media

OBJECTIVES

The purpose of this study was to examine the potential of intravascular gadolinium (Gd)-chelates in discriminating acute from chronic myocardial infarctions (MIs).

BACKGROUND

A potential limitation of delayed contrast enhanced magnetic resonance imaging with standard extracellular Gd-chelates is its inability to distinguish acute from chronic MIs.

METHODS

Eight pigs with MIs were studied at 3 days and 8 weeks. Inversion recovery gradient echo (IR-GRE), T(1)-turbo spin echo (TSE), and T(2)-TSE images were acquired before and after administration of intravascular and extracellular Gd-chelates. Triphenyltetrazolium chloride (TTC) was used to delineate infarctions at postmortem. Masson's trichrome and Biotinylated Bandeiria simplicifolia Isolectin B4 stains were used to characterize scarred myocardium. Analysis of variance was used to compare signal intensity (SI) ratios and determine differences in infarct extent.

RESULTS

The intravascular agent produced differential enhancement of acute infarctions at 3 days (SI ratio 5.8 +/- 1.3) but not at 8 weeks (1.6 +/- 0.4, p < 0.01). The extracellular agent provided differential enhancement of both acute (SI ratio 7.7 +/- 1.4) and chronic (7.5 +/- 0.9) infarctions. The extents of enhanced regions in acute infarctions were not different after intravascular (16.0 +/- 1.3%) or extracellular (17.1 +/- 1.7%) agents; at 8 weeks the extent of extracellular enhanced and TTC regions were smaller (13.2 +/- 1.4% and 12.0 +/- 1.5%, respectively). Masson's trichrome stain demonstrated dense scar tissue, signaling the complete healing of infarction. The vascular stain showed that scar tissue contained fewer microvessels oriented in a haphazard array.

CONCLUSIONS

The combination of intravascular and extracellular Gd-chelates discriminates acute from chronic infarctions on delayed images. This double contrast agent approach can be used to determine the age and extent of infarctions.

Myocardial viability: assessment with three-dimensional MR imaging in pigs and patients

PURPOSE

To prospectively evaluate the correlation between a three-dimensional (3D) delayed enhancement magnetic resonance (MR) imaging sequence and a two-dimensional (2D) delayed enhancement MR imaging sequence for noninvasive assessment of myocardial viability in pigs and patients.

MATERIALS AND METHODS

The pig and patient studies were approved by the responsible authorities, and patients gave written informed consent. MR imaging was performed by using a rapid 3D inversion-recovery balanced steady-state free precession sequence and a 2D segmented inversion-recovery fast low-angle shot sequence as the reference standard. Fourteen pigs with reperfused (n=7) or nonreperfused (n=7) myocardial infarction and 17 patients (13 men, four women; mean age, 64.9 years+/-8.6 [standard deviation]) suspected of having myocardial infarction were included. Linear regression analysis and Bland-Altman analysis were used to compare the infarction volumes.

RESULTS

In 10 of the 14 pigs the induction of myocardial infarction was successful. In these pigs, altogether 81 segments with myocardial infarction were demonstrated by both MR sequences, and agreement between the two sequences for classification of transmural extent of myocardial infarction was 99.7%. The infarction volume determined by using 3D MR imaging (4.64 cm3+/-2.48) in the pigs highly correlated with that of 2D MR imaging (4.65 cm3+/-2.39, r=0.989, P<.001) and that of staining by using triphenyltetrazolium chloride (4.67 cm3+/-2.44, r=0.996, P<.001). Thirteen of the 17 patients examined showed myocardial infarction in 34 myocardial segments with both sequences, and agreement between the two sequences for classification of transmural extent of myocardial infarction was 98.6%. In the patients, the infarction volume determined with both sequences highly correlated (9.71 cm3+/-7.47 for the 3D sequence vs 10.01 cm3+/-8.04 for the 2D sequence, r=0.982, P<.001). The breath-hold time necessary for the 3D MR imaging (21.0+/-2.3 seconds) was significantly shorter than that for 2D MR imaging (188.3+/-20.2 seconds, P<.001).

CONCLUSION

Myocardial infarction volumes obtained with the 3D MR imaging sequence are highly correlated and in good agreement with volumes obtained with the 2D MR imaging standard approach and reduced the acquisition time by a factor of nine.

Contrast agents and cardiac MR imaging of myocardial ischemia: from bench to bedside

This review paper presents, in the first part, the different classes of contrast media that are already used or are in development for cardiac magnetic resonance imaging. A classification of the different types of contrast media is proposed based on the distribution of the compounds in the body, their type of relaxivity and their potential affinity to particular molecules. In the second part, the different uses of the extracellular type of T1-enhancing contrast agent for myocardial imaging is covered from the detection of stable coronary artery disease to the detection and characterization of chronic infarction. A particular emphasis is placed on the clinical use of gadolinium-chelates, which are the universally used type of MRI contrast agent in the clinical routine. Both approaches, first-pass magnetic resonance imaging (FP-MRI) as well as delayed-enhanced magnetic resonance imaging (DE-MRI), are covered in the different situations of acute and chronic myocardial infarction.

Single-session magnetic resonance coronary angiography and myocardial perfusion imaging using the new blood pool compound B-22956 (gadocoletic acid): initial experience in a porcine model of coronary artery disease

OBJECTIVE

The objective of this study was to evaluate a new blood pool contrast agent, B-22956, for detecting myocardial perfusion abnormality and coronary artery stenosis by magnetic resonance imaging (MRI) in 1 setting.

MATERIALS AND METHODS

Coronary artery atherosclerotic stenoses were created in 6 miniswine. Myocardial first-pass perfusion imaging was performed with a bolus injection of 0.015 mmol/kg B-22956 during pharmacologic stress followed by postcontrast coronary artery imaging after another injection of B-22956/1. The total doses for the 6 pigs were 0.1 mmol/kg (n=3) and 0.15 mmol/kg (n=3). Perfusion upslope maps were analyzed and MR coronary artery images were reviewed by 2 readers.

RESULTS

For all 6 pigs, the normalized upslopes of the perfusion curves were 0.83+/-0.12, 0.74+/-0.15, and 0.52+/-0.05 (P<0.01 vs. normal) with normal or mild (<50% area stenosis), moderate (<50% and <75%), and severe stenosis (>75%), respectively. Mean signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) in right coronary artery images improved 90% and 200%, respectively, with a total dose of 0.1 mmol/kg of B-22956. Excellent agreements (kappa=0.82) were achieved for evaluating the grade of stenosis between MR postcontrast coronary artery images and histopathology by 2 reviewers.

CONCLUSION

The MR blood pool contrast agent B-22956 demonstrated the ability for detecting myocardial perfusion abnormalities and coronary artery stenosis in 1 setting.

How to compare the efficiency of albumin-bound and nonalbumin-bound contrast agents in vivo: the concept of dynamic relaxivity

RATIONALE AND OBJECTIVES

The objective of this study was to compare, in a rabbit experimental model that mimics a magnetic resonance (MR) angiographic protocol, the efficiency of the following types of compound on the MR signal: (1) a nonalbumin-bound blood pool contrast agent: P792; (2) a weak albumin-bound extracellular contrast agent: Gd-BOPTA; and (3) a strong albumin-bound blood pool contrast agent: MS325.

METHODS

The 2 main phases of early distribution after contrast agent injection, ie, the bolus phase (0-15 seconds postinjection) and the postbolus phase (1-5 minutes postinjection) were investigated by measuring Gd blood concentrations in the first 5 minutes postinjection. In the case of MS325 and Gd-BOPTA, the percentage of the free and bound forms were calculated throughout the pharmacokinetic profile. The dynamic relaxivity at 60 MHz in plasma of each contrast agent was determined in the 2 phases after contrast agent injection, ie, the bolus phase and the postbolus phase.

RESULTS

Injected under similar conditions, the 3 contrast agents had a comparable profile during the bolus phase (0-15 seconds postinjection). At 1 minute postinjection, only 38% of Gd-BOPTA remained in the blood, whereas 85% of P792 was still present in the blood. MS-325 had an intermediate position with 61% remaining in the blood. During the postbolus phase, the various compounds demonstrated similar behavior: the plasma concentration of P792 was higher than that of MS325 and Gd-BOPTA, ie, Ci/C0 (P792)>Ci/C0 (MS325)>Ci/C0 (Gd-BOPTA). At the peak of the bolus, 75% of MS325 and 93% of Gd-BOPTA was present in free form. This proportion decreased progressively during the postbolus phase, because 5 minutes postinjection, 23% of the free form remained for MS325 and 82% for Gd BOPTA. A significant decrease in dynamic r1 relaxivity was observed at 60 MHz for the products that bind to albumin (Gd-BOPTA and MS325) during the bolus phase. The dynamic relaxivity for MS325 at the bolus phase was 8.6 mMs and 5.2 mMs for Gd-BOPTA. At the postbolus phase, the dynamic relaxivity increased (17.3 mMs for MS325 and 6.7 mMs for Gd-BOPTA). The dynamic relaxivity of P792, which does not bind to albumin, was constantly equal to 26 mMs at each time point of the pharmacokinetic profile (bolus and postbolus phase).

CONCLUSIONS

The physicochemical measurements of relaxivity in plasma are made in vitro at a fixed concentration of gadolinium and the value of relaxivity is not necessarily an accurate reflection of the efficiency of the contrast agent in vivo, especially for contrast agents that bind to albumin. Indeed, in vivo, the proportion of free and bound forms of albumin-binding contrast agents varies according to the pharmacokinetic profile, and the relaxivities of albumin-bound and free contrast agents are different. Consequently, the concept of dynamic relaxivity was introduced to compare the efficiency of MS325, Gd-BOPTA, and P792 in vivo. The variation of the dynamic relaxivity of MS325 and Gd-BOPTA between the bolus and postbolus phase is significant (101% for MS325 and 29% for Gd-BOPTA) as a result of the variation in the quantity of bound and free forms during the pharmacokinetic profile. The blood pool agent P792 has different properties, which result from its intravascular retention and its lack of albumin binding. Indeed, contrary to Gd-BOPTA and MS325, the dynamic relaxivity of P792 is higher at the bolus phase (26 mMs) and does not vary during the pharmacokinetic profile. The impact of these different dynamic relaxivities should be integrated in the analysis of the performance of the different classes of contrast agents in clinical MRA protocols.

A feasibility study of contrast enhancement of acute myocardial infarction in multislice computed tomography: comparison with magnetic resonance imaging and gross morphology in pigs

INTRODUCTION

Late enhancement magnetic resonance imaging (MRI) of myocardial infarction (MI) is clinically established. There are no reports on MI assessment using state-of-the-art multislice CT technology. For this reason, animal experiments were conducted to examine the applicability of contrast-enhanced ECG-gated multislice computed tomography (MSCT) for the detection of acute MI. The results were correlated with MRI and postmortem tissue staining.

MATERIAL AND METHODS

Acute MI was induced in 14 pigs by balloon occlusion of the LAD. In 8 animals, the LAD was reperfused after 45 minutes. In 6 animals, the LAD was permanently blocked. MR imaging was performed 15 minutes after the administration of 0.2 mmol Gd-DTPA/kg/bodyweight. Subsequently, 16-slice MSCT was performed at various timepoints after injecting 120 mL of iodinated contrast medium. 2,3,5-Triphenyltetrazolin-chloride (TTC) staining was acquired for all hearts investigated. Correlation analysis was applied to compare the area of MI derived from MRI, MSCT, and TTC. The reperfused infarcts were compared with the nonreperfused infarcts using an unpaired t test.

RESULTS

: Mean infarct area as measured by TTC staining was 18.3% +/- 7.8% of the left ventricular area. Good correlation of the spatial extent of the infarcted area was found for TTC and MRI as well as for TTC and MSCT data obtained 5 minutes postcontrast injection. MSCT imaging demonstrated a significant difference in density (P < 0.001) between nonreperfused (47.0 +/- 6.6 HU) and reperfused (116.4 +/- 19.8 HU) infarction.

CONCLUSION

In our pilot study, contrast-enhanced MSCT was feasible to assess myocardial viability in pigs. MSCT also affords differentiation of nonreperfused and reperfused acute MI. MI sizes derived from MSCT imaging correlate well to those obtained with MRI and TTC.

Automatic fuzzy classification of the washout curves from magnetic resonance first-pass perfusion imaging after myocardial infarction

OBJECTIVES

We sought to investigate the diagnostic ability of cardiac magnetic resonance imaging (MRI) perfusion in acute reperfused myocardial infarction. The study used fuzzy logic to automatically classify signal intensity-time curves from myocardial segments into 3 categories: normal, hypointense, and Hyperintense.

MATERIALS AND METHODS

Thirty-eight patients with myocardial infarction underwent short-axis cine-MRI and contrast-enhanced MRI to provide data on wall thickening and the transmural extent of infarction. Of these, 17 had a second cardiac MRI to ascertain the functional recovery in each segment.

RESULTS

The fuzzy logic based classification performs well (kappa= 0.87, P < 0.01) in comparison with a visual approach. Segments providing "hypo" curves do not recover (Delta = 0.11 SD = 0.96) whereas segments demonstrating the other curve types recover (Delta = 1 SD = 1.98 for "hyper" curves and Delta = 1.54 SD = 1.77 for "normal" curves).

CONCLUSIONS

The proposed automatic signal intensity-time curve classification has a prognostic value when studying the functional recovery of pathologic segments and clearly identifies the no-reflow phenomenon known to induce poor recovery.

Multiview active appearance models for simultaneous segmentation of cardiac 2- and 4-chamber long-axis magnetic resonance images

RATIONALE AND OBJECTIVES

Long-axis cardiac magnetic resonance (MR) views enable a rapid, online evaluation of cardiac function from only 2 views. In this article, we aimed to evaluate a model-based method for the simultaneous detection of 2- and 4-chamber endocardial and epicardial contours in end-diastolic and end-systolic phases of MR images.

METHODS

We introduce multiview Active Appearance Models for the automated segmentation of long-axis cardiac MR images of the left ventricle. Two modes of initialization were used to test the accuracy of the model with minimal user interaction and the best-obtainable accuracy with this model. The segmentation was initialized by annotating 2 points in the base and one in the apex. We tested the method's performance by comparing the point-to-curve errors, ejection fractions, and biplane area-length volumes calculated with the automatically detected contours to those calculated from contours that were annotated manually by experts. Leave-one-out experiments were performed with 2- and 4-chamber long axis MR images of 59 subjects in end-diastolic and end-systolic phases.

RESULTS

When initializing in all 4 frames, 97% of the segmentations were successful, and the standard deviation in the volume-errors with respect to the average manually identified volume was 9.0% for the end-diastolic volumes and 15% for the end-systolic volumes. When the method was initialized in the end-systolic frames only, 92% of the segmentations were successful, and the standard deviation in the errors in the volumes with respect to the average manually identified volume was 13.3% for the end-diastolic volumes and 16.7% for the end-systolic volumes. Bland-Altman plots showed that the errors were distributed randomly around 0, and by using a paired t test comparing manual and computer-determined volumes, we were able to detect that the volume differences were not significant. Simultaneous detection of the endocardial and epicardial contours in 2- and 4-chamber views and end-diastolic and end-systolic phases for one subject takes approximately 3 seconds.

CONCLUSIONS

The accuracy of the reported method is comparable with the interobserver variability for initialization in all frames and slightly worse than the interobserver variability with initialization in the end-systolic frames only. However, in both cases the errors were not significant. Initialization in end-systolic frames only leads to a statistically insignificantly lower model accuracy; however, it requires only half the user interaction. Therefore, we can conclude that this method enables rapid analysis of the cardiac left ventricular function with little user interaction.

Renal Functional Contrast-Enhanced Magnetic Resonance Imaging

OBJECTIVES

The objective of the present study was to compare P792, a new rapid clearance blood pool agent characterized by negligible interstitial diffusion but unrestricted glomerular filtration, with Gd-DOTA in both qualitative and quantitative aspects of renal functional magnetic resonance imaging.

MATERIALS AND METHODS

Dynamic imaging was performed with a fast T1-weighted gradient-echo sequence on a 1.5-T magnet in 25 Sprague-Dawley rats, after injection of 13 micromol Gd/kg-1 of P792 (n = 10), 100 (n = 10), or 50 micromol Gd/kg-1 of Gd-DOTA (n = 5). Signal-time curves from 6 regions of interest (ROIs), including renal parenchyma and contents, were analyzed.

RESULTS

Qualitative analysis depicted a typical pattern of temporal enhancement as previously described with extracellular gadolinium chelates, including early and brief enhancement of the aorta, renal vessels and cortex, quickly followed by enhancement of the medulla and then renal pelvis. However, a decrease in signal intensity was noted in the inner medulla and the renal pelvis approximately 90 seconds after bolus injection, being more marked when using the full dose of Gd-DOTA. Curve analysis showed a similar vascular phase within each parenchymal ROI, confirmed by similar upslopes, which ranged from 0.015 +/- 0.007 to 0.019 +/- 0.005. Following this initial phase, T1-enhancement appeared greater and longer within the medulla and renal pelvis, and subsequently in the whole kidney ROI with P792 (time to maximal enhancement (sec)/ enhancement rate: 85.5 +/- 15.9/3.1 +/- 0.4) as compared with Gd-DOTA full (53.0 +/- 18.9/ 2.7 +/- 0.3) or half dosage (65.2 +/- 20.1/ 2.2 +/- 0.2). The subsequent decrease in signal intensity, characterized by a downslope during the minute following maximal enhancement, was faster with Gd-DOTA (0.006 +/- 0.002) as compared either to P792 or half dosage Gd-DOTA (0.003 +/- 0.001).

CONCLUSIONS

Due to its physicochemical and pharmacokinetic properties, P792 allows the use of a reduced dosage of gadolinium, resulting in less T2* effect without compromising T1 enhancement. Thus, P792 appears suitable for renal functional MR imaging.

Gd(ABE-DTTA)-enhanced cardiac MRI for the diagnosis of ischemic events in the heart

PURPOSE

To demonstrate that contrast-enhanced MRI (ceMRI) with the aid of Gd(ABE-DTTA) is able to detect ischemic events in the heart in a canine ischemia/reperfusion (30/40 minutes) model.

MATERIALS AND METHODS

ECG-gated, T1-weighted MR image sets (four to five slices each) with three-minute time resolution were collected in transiently LAD-occluded dogs. Following the acquisition of control image sets, ischemia was started by occluding the LAD. Either Gd(ABE-DTTA) (N = 6) or Gd(DTPA) (N = 6) was injected, and imaging was continued for 30 minutes of ischemia and 40 minutes of reperfusion. The contrast agent (CA)-induced MRI signal intensity enhancement (SIE) and contrast were monitored. Microspheres measured myocardial perfusion (MP) to verify areas of ischemia and reperfusion.

RESULTS

SIEs of 86% +/- 3% and 97% +/- 3% in nonischemic, and 25% +/- 5% and 29% +/- 8% in ischemic regions were found within three minutes of onset of ischemia with Gd(ABE-DTTA) and Gd(DTPA), respectively. For the rest of the 30 minutes of ischemia, with Gd(ABE-DTTA) SIE of 60% +/- 3% and 25% +/- 5% persisted in the nonischemic and ischemic regions, respectively. With Gd(DTPA), however, SIE in the nonischemic areas decreased rapidly after the first three minutes of ischemia, while SIE in the ischemic areas increased, abolishing contrast. Thus, there was a persistent contrast with Gd(ABE-DTTA) and a short-lived contrast with Gd(DTPA) during ischemia. Furthermore, with Gd(ABE-DTTA) some contrast was still visible in the early reperfusion period.

CONCLUSION

Gd(ABE-DTTA) in an ischemia/reperfusion model induces a persistent MRI contrast between regions of normal and ischemic myocardium, and verifies reperfusion. Therefore, it can be used to detect myocardial ischemic events.