Cardiac T1 calculations from MR spin-echo images

Transesophageal cardiac pacing during magnetic resonance imaging: feasibility and safety considerations

The feasibility and safety of transesophageal cardiac pacing during clinical MRI at 1.5 Tesla is considered. An MRI compatible pace catheter was developed. In vitro testing showed a normal performance of the pulse generator, image artifacts that extended less than 11 mm from the catheter, and a less than 5% increase in noise. Cardiac stimulation induced by MRI was not observed and, theoretically, is not expected. Potentially, tissue around the catheter tip may become heated. This heating (delta tau) was monitored. Eight dogs were exposed to MRI during pacing. For low RF radiation exposure, a time-averaged squared B1 field below 0.08 p tau 2 (SAR < 0.03 W/kg), delta tau was below 1 degree C. For high RF radiation exposure, but at normal RF radiation specific absorption rate (0.4 W/kg) delta tau was 5 degrees C. Thus, transesophageal atrial pacing during MRI at low RF exposure seems to be possible to perform cardiac stress studies or to correct unstable heart rates.

Comparison of T1 estimation techniques in cardiac MRI

We have shown that the use of a simple combination of inversion recovery/spin-echo (IR/SE) sequences provides undeniably superior precision in quantitative in vivo myocardium T1 estimation than the standard multiple spin-echo approach. On a group of 25 healthy subjects, the T1 dispersion was, respectively, 3.8% for the IR/SE combination and 19.6% for the best SE pair combination. Moreover, repeated measurements were carried out on seven of the volunteers in order to assess T1 reproducibility. The mean intra-individual T1 precision was found to be 2.8% for the IR/SE pair and 20.0% for the best SE pair. The in vivo imaging work was supported and corroborated by a thorough treatment of the theoretical T1 errors. We also highlight the importance of quality control in quantitative MRI; a correction being required in the SE sequences to bring measured signal intensities into line with those predicted from simple theory.

Synchronized inversion recovery-spin echo sequences for precise in vivo T1 measurement of human myocardium: a pilot study on 22 healthy subjects

An ECG-triggered, two-sequence MRI technique is proposed for the precise measurement of proton T1 relaxation times of the human myocardium at a field strength of 0.5 T. The combination of an inversion recovery (IR) sequence and a spin echo (SE) sequence is not new. It is, however, rarely used in quantitative in vivo cardiac studies. Our approach employs a synchronization of the 90 degrees read pulse to the systolic period. In a study of 22 healthy volunteers, the globally measured T1 value was estimated to be 714 +/- 23 ms. Four of the volunteers also underwent additional imaging scans for the purposes of reproducibility assessment. The T1 precision was found to be 3.9 +/- 1.1% for the IR/SE combination and 16.9 +/- 5.3% for a combination of SE sequences. Total imaging time for the IR and SE sequences was 19.2 +/- 3.0 mins. The relative rapidity of this classic technique and the T1 precision obtained give this technique an obvious application in the discrimination of normal and diseased myocardium. In the same study, valuable supplementary tissue characterization is provided by T2, calculated from the SE sequence. T2 was evaluated to be 50 +/- 3 ms.

Serial nuclear magnetic resonance imaging of acute myocardial infarction with and without reperfusion

To compare nuclear magnetic resonance (NMR) image-derived T1 and T2 changes during evolving infarction, 14 dogs were studied serially: (1) 1 to 2 hours after left anterior descending coronary occlusion, (2) 2 to 3 hours after coronary occlusion (n = 7) or in the first hour after reperfusion following 2 hours of occlusion (n = 7), and (3) 5 days and (4) 21 days after occlusion/reperfusion. In addition, the extent of T1 and T2 abnormalities was compared to the extent of infarction as determined histologically for each set of images. With sustained coronary occlusion, an increase versus control values (T1 = 351 +/- 11 msec; T2 = 41 +/- 2 msec) was observed in the second hour after occlusion (T1 = 448 +/- 51 msec; T2 = 51 +/- 8 msec), gradually reaching a maximum by day 5 (T1 = 490 +/- 64 msec; T2 = 63 +/- 9 msec). By 21 days, T1 had decreased to 427 +/- 43 msec and T2 to 55 +/- 11 msec. However, with myocardial reperfusion, an abrupt increase in both T1 and T2 occurred compared to prereperfusion values in the first hour after release of occlusion, from 445 +/- 32 msec to 555 +/- 65 msec and from 52 +/- 5 msec to 65 +/- 8 msec, respectively. Subsequently, T1 remained elevated whereas T2 normalized. Only on day 21 images was there a good correlation between the extent of T1 and T2 abnormalities and infarct size, in both nonreperfused (r = 0.87; p less than 0.05), and reperfused (r = 0.89; p less than 0.01) dogs.(ABSTRACT TRUNCATED AT 250 WORDS)

Diagnostic applicability of magnetic resonance imaging in assessing human cardiac allograft rejection

To assess the diagnostic applicability of magnetic resonance imaging (MRI) for diagnosis of cardiac allograft rejection, 25 patients who recently underwent cardiac transplantation were studied on a 0.15-tesla resistive system within 24 hours of endomyocardial biopsy. Ten normal volunteers and 4 patients who had recent (within 2 weeks) nontransplant cardiac surgery were also studied. In the 19 transplant patients imaged within 24 days of graft implantation, only 1 had evidence of graft rejection on biopsy. However, all nonrejecting grafts had increased T1 and T2 values, 501 +/- 22 and 61 +/- 6 ms, respectively (mean +/- standard deviation) and the only rejecting graft had values of 496 and 60 ms, respectively. In the normal volunteers mean T1 was 352 +/- 18 ms and T2 was 35 +/- 6 ms. There was no significant difference in T1 and T2 values between patients who underwent nontransplant surgery and control subjects. In patients with nonrejecting transplants who were imaged more than 25 days after surgery, the T1 and T2 values had normalized to 359 +/- 17 ms and 36 +/- 7 ms, respectively (n = 28 images in 20 patients). However, in those grafts with rejection, T1 and T2 were both elevated to 502 +/- 21 ms and 62 +/- 6 ms, respectively (n = 15 in 13 patients); wall thickness was also increased. Fourteen of 15 late rejection events (more than 25 days after surgery) were correctly identified on the basis of increases in T1 and T2 to more than 2 standard deviations above normal.(ABSTRACT TRUNCATED AT 250 WORDS)