Ian L. Pykett

Quantification of experimental myocardial infarction using nuclear magnetic resonance imaging and paramagnetic ion contrast enhancement in excised canine hearts.

Determination of myocardial infarct size is important for clinical management of patients with ischemic heart disease and for research on limiting infarct size. Nuclear magnetic resonance (NMR) imaging permits tomographic depiction of the distribution of mobile tissue protons. NMR imageshave demonstrated high spatial resolution and contrast. To evaluate the potential of this technique in measuring myocardial infarct size, NMR imaging was performed in six canine hearts excised 24 hours after circumflex coronary artery ligation. Before sacrifice, the dogs received i.v. manganous chloride (0.05 mmol/kg). After NMR imaging, the hearts were sectioned and the myocardial slices were stained with triphenyl tetrazolium chloride. The pathologically determined infarct size was compared with the infarct size measured by NMR imaging. The correlation was good (regression line slope 1.06; r= 0.94). We conclude that NMR imaging with paramagnetic contrast agents canbe used to determine infarct size in excised hearts.

Measurement of spin-lattice relaxation times in nuclear magnetic resonance imaging

The diagnostic utility of proton (1H) nuclear magnetic resonance (NMR) imaging is greatly enhanced when the image is weighted with proton relaxation time information. The authors indicate factors affecting the accuracy of such measurements (especially with respect to T1 determination) and, specifically, the accuracy of one approach which has been used in their laboratory is assessed. A brief discussion pertaining to the validity of data obtained from biological material is presented.

Central pontine myelinolysis: Demonstration by nuclear magnetic resonance

An alcoholic, hyponatremic woman developed central pontine myelinolysis (CPM) and improved from a decerebrate, comatose state to alertness and full ambulation. NMR, using inversion-recovery and spin-echo pulse sequences, was performed sequentially from 4 weeks to 8 months after onset of symptoms and revealed a well-defined lesion with prolonged relaxation times. The lesion was anatomically consistent with CPM and was initially also visualized by CT. NMR showed no definite temporal change in the qualitative appearance of the lesion until the 8-month scan; however, quantitatively, a reduction of relaxation times was noted with each serial study.

Nuclear magnetic resonance (NMR) imaging of tumors in the posterior fossa.

Nuclear magnetic resonance (NMR) images were obtained in 12 patients with mass lesions in the posterior fossa and the results compared with X-ray computed tomography (CT). Inversion recovery T1-weighted images demonstrated abnormalities in six of six intrinsic lesions and three of six extrinsic lesions. Spin echo T2-weighted images demonstrated abnormalities in two of two intrinsic lesions and four of five extrinsic lesions. Saturation recovery T1-weighted images were normal in two of two intrinsic lesions and two of four extrinsic lesions. Overall, NMR detected 11 of 12 lesions. Two intrinsic tumors detected by NMR were not detected by CT evaluation. Two small extrinsic tumors required CT gas cisternography for detection.

Proton NMR imaging in experimental ischemic infarction.

Proton nuclear magnetic resonance (NMR) images depict the distribution and concentration of mobile protons modified by the relaxation times T1 and T2. Using the steady-state-free-precession (SSFP) technique, serial coronal images were obtained sequentially over time in laboratory animals with experimental ischemic infarction. Image changes were evident as early as 2 hours after carotid artery ligation, and corresponded to areas of ischemic infarction noted pathologically. Resulting SSFP images in experimental stroke are contrasted to inversion-recovery NMR images in an illustrative patient with established cerebral infarction. Bulk T1 and T2 measurements were made in vitro in three groups of gerbils: normal, those with clinical evidence of infarction, and those clinically normal after carotid ligature. Infarcted hemispheres had significantly prolonged T1 and T2 (1.47 +/− .12 sec, 76.0 +/− 9.0 msec, respectively) when compared to the contralateral hemisphere (T1 = 1.28 +/− .05 sec, T2 = 58.7 +/− 3.9 msec) or to the other two groups. These data suggest that changes in NMR parameters occur and can be detected by NMR imaging as early as two hours after carotid artery ligation.

True three-dimensional nuclear magnetic resonance neuro-imaging in ischemic stroke: correlation of NMR, X-ray CT and pathology.

True three-dimensional proton nuclear magnetic resonance (NMR) imaging was performed on an 84-year-old man following a recent cerebral embolic infarction. NMR data obtained using different pulse sequences were inter-correlated, stressing the significance of image appearance in terms of the NMR tissue parameters. Planes selected for display from the three-dimensional data set allowed optimal visualization of the pathology. Accurate correlations of the NMR data with X-ray computerized tomography scans and with subsequent autopsy findings indicate that NMR may play an important role in the detection and diagnosis of ischemic stroke.

Nuclear magnetic resonance (NMR) imaging of Arnold-Chiari type I malformation with hydromyelia

Saturation recovery nuclear magnetic resonance (NMR) images and metrizamide computed tomography (CT) scans were obtained in an adult patient with a clinical history suggestive of syringomyelia. Both NMR and CT studies showed low lying cerebellar tonsils. The CT study demonstrated central cavitation of the spinal cord from the midthoracic to midcervical levels but could not exclude an intramedullary soft tissue mass at the cervico-medullary junction. The NMR images in transverse, coronal, and sagittal planes demonstrated extension of an enlarged central spinal cord cerebrospinal fluid space to the cervico-medullary junction. This was felt to be strong evidence for exclusion of an intramedullary soft tissue mass and in favor of a diagnosis of Arnold-Chiari Type I malformation with hydromyelia. The noninvasive nature of spinal cord and cervico-medullary junction evaluation with NMR is emphasized.

Clinical relevance of two different nuclear magnetic resonance (NMR) approaches to imaging of a low grade astrocytoma.

A young patient with progressive neurological deficit of uncertain cause underwent true three-dimensional nuclear magnetic resonance (NMR) imaging by the inversion-recovery and by the saturation-recovery techniques. Differences between the results of the two methods helped clarify the nature of the underlying disorder and revealed an extent of neoplasia greatly exceeding that suggested by X-ray computed tomography. The NMR imaging results were instrumental in selecting the site for brain biopsy, which demonstrated a Grade II astrocytoma.

Techniques and approaches to proton NMR imaging of the head

The next few years will undoubtedly see a refinement of proton imaging technology and a broader data base will indicate to what extent proton relaxation parameters are able to detect and characterize disease. In addition, it is likely that imaging of other nuclei (e.g. 31P, 23Na, 19F) will become a reality, although it must be stated that due to their inherently lower sensitivity to NMR detection and/or lower physiological concentration, clinical images of nuclei other than 1H will undoubtedly have a low spatial resolution and may require relatively long imaging times [41]. Nonetheless, herein lies the exciting possibility of non-invasive metabolic or functional imaging [42]. The realm of NMR contrast agents is just beginning to be explored [43, 44], and developments in high-speed imaging [45] indicate useful applications in cardiology [46]. So whilst improvements in image quality can be expected, as was the case with X-ray CT, the application of NMR in medicine will diversify to yield information of a more specifically functional nature. This, together with the very low attendant biological risk [47], heralds a bright future for NMR in clinical diagnosis.

Contrast induced myocardial signal reduction: Effect of lanthanide chelates on ultra high speed MR images

The myocardial MR signal reduction associated with an intravenous bolus of Gd-DTPA and Dy-DTPA was studied in a canine model. Imaging was performed with a high speed echo-planar type imaging system (Instascan, Advanced NMR Systems, Inc.). Gated spin-echo images were obtained with TE of 30 ms, which permits image acquisition in approximately 40 ms. The gated TR was dependent on the heart rate, with an average TR of 2.4 s. After 0.1 mmol/kg of contrast was injected, 70 images were acquired, which showed in an 80-image data set a reduction in myocardial signal with a gradual return to normal. After dipyridamole infusion, the signal loss was significantly more pronounced, and earlier than in the control data set. There was no significant difference between Gd-DTPA and Dy-DTPA in these imaging studies despite the theoretical prediction of better Dy signal reduction, possibly due to physiological variability during the course of a study or between studies. The cause of enhanced contrast effect after dipyridamole infusion is discussed, as is the basis for dipyridamole enhancement, and the possible role of contrast enhanced MR imaging in the detection of cardiac disease.