Differentiation of cardiac ischemia and rejection by nuclear magnetic spectroscopy

Post-mortem cardiac 3-T magnetic resonance imaging: visualization of sudden cardiac death?

OBJECTIVES

This study aimed to investigate post-mortem magnetic resonance imaging (pmMRI) for the assessment of myocardial infarction and hypointensities on post-mortem T2-weighted images as a possible method for visualizing the myocardial origin of arrhythmic sudden cardiac death.

BACKGROUND

Sudden cardiac death has challenged clinical and forensic pathologists for decades because verification on post-mortem autopsy is not possible. pmMRI as an autopsy-supporting examination technique has been shown to visualize different stages of myocardial infarction.

METHODS

In 136 human forensic corpses, a post-mortem cardiac MR examination was carried out prior to forensic autopsy. Short-axis and horizontal long-axis images were acquired in situ on a 3-T system.

RESULTS

In 76 cases, myocardial findings could be documented and correlated to the autopsy findings. Within these 76 study cases, a total of 124 myocardial lesions were detected on pmMRI (chronic: 25; subacute: 16; acute: 30; and peracute: 53). Chronic, subacute, and acute infarction cases correlated excellently to the myocardial findings on autopsy. Peracute infarctions (age range: minutes to approximately 1 h) were not visible on macroscopic autopsy or histological examination. Peracute infarction areas detected on pmMRI could be verified in targeted histological investigations in 62.3% of cases and could be related to a matching coronary finding in 84.9%. A total of 15.1% of peracute lesions on pmMRI lacked a matching coronary finding but presented with severe myocardial hypertrophy or cocaine intoxication facilitating a cardiac death without verifiable coronary stenosis.

CONCLUSIONS

3-T pmMRI visualizes chronic, subacute, and acute myocardial infarction in situ. In peracute infarction as a possible cause of sudden cardiac death, it demonstrates affected myocardial areas not visible on autopsy. pmMRI should be considered as a feasible post-mortem investigation technique for the deceased patient if no consent for a clinical autopsy is obtained.

The role of magnetic resonance imaging and spectroscopy in transplantation: from animal models to man

Critical success factors in solid organ and vascular transplantation are the assessment of graft status/viability as well as stringent monitoring of transplant recipients, preferentially using noninvasive techniques. This review addresses the application of magnetic resonance imaging (MRI) and spectroscopy (MRS) in the field of transplantation. The first section is devoted to the description of the main MR techniques used for monitoring the status of the graft noninvasively. Subsequently, the role of MRI/MRS in the analysis of the viability of organs for transplantation is discussed. Since chronic rejection remains a major difficulty, development of new therapies is still ongoing. Thus, the third part is devoted to the use of MRI/MRS for monitoring graft rejection in animal models of transplantation. This is followed by a discussion of clinical studies of transplantation involving MRI/MRS. Finally, a general appraisal is made on available imaging techniques for the non-invasive characterization of grafts in situ, highlighting the role of MR methods in the field of transplantation.

The detection of chronic heart graft rejection by 31P NMR spectroscopy

The usefulness of phosphorus-31 nuclear magnetic resonance spectroscopy (31P NMRS) for detecting heart graft rejection after transplantation has been investigated by several researchers, and it has thus been demonstrated to be a valid technique for detecting acute myocardial rejection. In this study, we investigated the value of 31P NMRS to assess chronic cardiac allograft rejection. Lewis rat hearts were transplanted into the femoral region of F-344 rat recipients which were treated with cyclosporine, 5mg/kg body weight, by a daily intramuscular injection for 30 days beginning on the day of transplantation. The control isografts employed Lewis donors and recipients not given cyclosporine. The ratios of phosphocreatine (PCr) to inorganic phosphate (Pi), beta-adenosine triphosphate (beta-ATP) to Pi, and PCr to beta-ATP were monitored using surface coil 31P NMRS. 31P NMRS was performed 3, 30, and 60 days after transplantation, and the degree of the rejection and arteriosclerosis of the coronary arteries were then assessed histologically. The PCr:Pi and beta-ATP:Pi ratios for the allografts demonstrated a significant decrease on postoperative day (POD) 60 from that on POD 30 (PCr:Pi, P < 0.001; beta-ATP:Pi, P < 0.01). Although a significant difference existed between the isografts and allografts on POD 60 (PCr: Pi, P < 0.01; beta-ATP:P, P < 0.01), no significant difference was found in the PCr:beta-ATP ratio between the allografts and the isografts. On POD 60, the allografts showed significant graft rejection and arteriosclerotic changes in the coronary arteries. These findings therefore demonstrated the effectiveness of 31P NMRS for detecting chronic graft rejection in a rat model.

Assessment of cardiac rejection by MR-imaging and MR-spectroscopy

BACKGROUND

Detection of cardiac rejection is a major problem in cardiac transplantation. The gold standard is, and remains, endomyocardial biopsy.

PURPOSE

Evaluation of MR-imaging and MR-spectroscopy for detection of cardiac rejection.

METHODS

Orthotopic cardiac transplantation (HTX) was performed in 13 pigs (body weight 30 kg). All animals obtained immunosuppressive (triple) therapy for 1 week after the operation. Thereafter immunosuppression was stopped to induce cardiac rejection. MRI and MRS (1.5 Tesla General Electrics Signa) were performed pre- and post-operatively on days 10, 17, 24 and 31. The degree of rejection was determined post-operatively using endomyocardial biopsy (Texas grading score).

RESULTS

(1) MR-imaging: LV function remained unchanged after HTX. LV mass increased (+42%; P < 0.05) with cardiac rejection. (2) MR-spectroscopy: a marked reduction in the ratio of phosphocreatine and adenosine triphosphate, respectively, to inorganic phosphate was observed in the rejecting hearts. (3) Histologic grading confirmed cardiac rejection after stopping immunosuppression. The Texas score was 5.7+/-0.8 at autopsy.

CONCLUSIONS

MR-imaging and MR-spectroscopy allow the detection of changes associated with cardiac rejection. Both techniques are correlated with histologic rejection. However, endomyocardial biopsy remains the gold standard for reliable detection of cardiac rejection.