Joint Reconstruction of Multiple Images and Motion in MRI: Application to Free-Breathing Myocardial T2Quantification.

Exploiting redundancies between multiple images of an MRI examination can be formalized as the joint reconstruction of these images. The anatomy is preserved indeed so that specific constraints can be implemented (e.g. most of the features or spatial gradients should be in the same place in all these images) and only the contrast changes from one image to another need to be encoded. The application of this concept is particularly challenging in cardiovascular and body imaging due to the complex organ deformations, especially with the patient breathing. In this study a joint optimization framework is proposed for reconstructing multiple MR images together with a nonrigid motion model. The motion model takes into account both intra-image and inter-image motion and therefore can correct for most ghosting/blurring artifacts and misregistration between images. The framework was validated with free-breathing myocardial T2 mapping experiments from nine heart transplant patients at 1.5 T. Results showed improved image quality and excellent image alignment with the multi-image reconstruction compared to the independent reconstruction of each image. Segment-wise myocardial T2 values were in good agreement with the reference values obtained from multiple breath-holds (62.5 ± 11.1 ms against 62.2 ± 11.2 ms which was not significant with p=0.49).

Nonrigid registration improves MRI T2 quantification in heart transplant patient follow-up.

BACKGROUND: To evaluate the use of a nonrigid registration technique for detecting acute heart transplant rejection by MRI T2 quantification. METHODS: Myocardial T2 quantification was achieved in 279 consecutive examinations from 78 different patients. The protocol consisted of 10 successive black-blood fast spin echo sequences with varying echo times, and a postprocessing based on image registration and exponential fitting. An automatic nonrigid registration method was applied to correct for myocardium misalignment. Finally T2 values were compared with those obtained with a conventional rigid registration followed by manual correction. RESULTS: Nonrigid registration was feasible in 98% of the datasets and was judged of higher quality compared with conventional processing (P < 0.001). No significant difference was found in the clinical outcome (average septal T2 ) between nonrigid and conventional registration (P = 0.66). Interobserver variability was improved with 95% limits of agreement of 2.7 ms (against 3.7 ms with conventional registration). The quality of T2 fitting, as assessed by the coefficient of determination R(2) , was significantly improved (P < 0.001). CONCLUSION: Nonrigid registration improves T2 quantification in heart-transplant patient follow-up.

Efficient extra- and intracellular alkalinization improves cardiovascular functions in severe lactic acidosis induced by hemorrhagic shock.

BACKGROUND: Lactic acidosis is associated with cardiovascular failure. Buffering with sodium bicarbonate is proposed in severe lactic acidosis. Bicarbonate induces carbon dioxide generation and hypocalcemia, both cardiovascular depressant factors. The authors thus investigated the cardiovascular and metabolic effects of an adapted sodium bicarbonate therapy, including prevention of carbon dioxide increase with hyperventilation and ionized calcium decrease with calcium administration. METHODS: Lactic acidosis was induced by hemorrhagic shock. Twenty animals were randomized into five groups: (1) standard resuscitation with blood retransfusion and norepinephrine (2) adapted sodium bicarbonate therapy (3) nonadapted sodium bicarbonate therapy (4) standard resuscitation plus calcium administration (5) hyperventilation. Evaluation was focused in vivo on extracellular pH, on intracellular pH estimated by P nuclear magnetic resonance and on myocardial contractility by conductance catheter. Aortic rings and mesenteric arteries were isolated and mounted in a myograph, after which arterial contractility was measured. RESULTS: All animals in the hyperventilation group died prematurely and were not included in the statistical analysis. When compared with sham rats, shock induced extracellular (median, 7.13; interquartile range, [0.10] vs. 7.30 [0.01]; P = 0.0007) and intracellular acidosis (7.26 [0.18] vs. 7.05 [0.13]; P = 0.0001), hyperlactatemia (7.30 [0.01] vs. 7.13 [0.10]; P = 0.0008), depressed myocardial elastance (2.87 [1.31] vs. 0.5 [0.53] mmHg/µl; P = 0.0001), and vascular hyporesponsiveness to vasoconstrictors. Compared with nonadapted therapy, adapted bicarbonate therapy normalized extracellular pH (7.03 [0.12] vs. 7.36 [0.04]; P < 0.05), increased intracellular pH to supraphysiological values, improved myocardial elastance (1.68 [0.41] vs. 0.72 [0.44] mmHg/µl; P < 0.05), and improved aortic and mesenteric vasoreactivity. CONCLUSIONS: A therapeutic strategy based on alkalinization with sodium bicarbonate along with hyperventilation and calcium administration increases pH and improves cardiovascular function.

Diagnostic and prognostic value of MRI T2 quantification in heart transplant patients.

This study was designed retrospectively to assess the value of myocardial T2 to detect or predict ongoing acute heart rejection, in heart transplant patients, with a 1.5-T MRI magnet. One hundred and ninety-six myocardial T2 quantifications were performed on sixty consecutive heart transplant patients during routine follow-up. T2 values were assessed (i) with regard to the results of concomitant biopsies and (ii) with a Cox multivariate model for the prediction of subsequent rejections, defined by a ≥ grade 2 at biopsy or highly suspected in the absence of biopsy (>10% drop in ejection fraction with subsequent reversibility under treatment). T2 values were proposed as main covariate, after logit transformation and adjustment for other confounding parameters such as delay since graft surgery and delay before biopsy. T2 values were strongly linked (i) to the presence of rejection on concomitant biopsy (P < 0.0001) and (ii) to the risk of subsequent rejection on Cox multivariate model (P < 0.001). T2 values above 60 ms were associated with relative risk of rejection higher than 2.0 and rapidly increasing. In conclusion, myocardial T2 yields a high diagnostic and prognostic value for graft rejection in heart transplant patients.

Effect of physiological heart rate variability on quantitative T2 measurement with ECG-gated Fast Spin Echo (FSE) sequence and its retrospective correction.

OBJECT: Quantitative T2 measurement is applied in cardiac Magnetic Resonance Imaging (MRI) for the diagnosis and follow-up of myocardial pathologies. Standard Electrocardiogram (ECG)-gated fast spin echo pulse sequences can be used clinically for T2 assessment, with multiple breath-holds. However, heart rate is subject to physiological variability, which causes repetition time variations and affects the recovery of longitudinal magnetization between TR periods. MATERIALS AND METHODS: The bias caused by heart rate variability on quantitative T2 measurements is evaluated for fast spin echo pulse sequence. Its retrospective correction based on an effective TR is proposed. Heart rate variations during breath-holds are provided by the ECG recordings from healthy volunteers. T2 measurements were performed on a phantom with known T2 values, by synchronizing the sequence with the recorded ECG. Cardiac T2 measurements were performed twice on six volunteers. The impact of T1 on T2 is also studied. RESULTS: Maximum error in T2 is 26% for phantoms and 18% for myocardial measurement. It is reduced by the proposed compensation method to 20% for phantoms and 10% for in vivo measurements. Only approximate knowledge of T1 is needed for T2 correction. CONCLUSION: Heart rate variability may cause a bias in T2 measurement with ECG-gated FSE. It needs to be taken into account to avoid a misleading diagnosis from the measurements.

Multicompartmental analysis of late contrast enhancement in areas of myocardial infarction supplied by chronically occluded coronary arteries.

PURPOSE: To analyze the relationship between late contrast enhancement (LCE) and the interstitial distribution volume (V(In)) of gadolinium (Gd) tracers in the myocardial infarction (MI) areas supplied by chronically occluded arteries from patients. In animal experimental models, LCE has already been shown to correspond to an enhanced V(In) of Gd tracers and thus, to a decrease in the amount of intact cells. MATERIALS AND METHODS: A multicompartmental analysis was applied to serial MRI images encompassing both infarct and remote areas and recorded with a conventional two-dimensional (2D) segmented inversion-recovery gradient-echo (IR-GRE) sequence during a 15-minute period following Gd-diethylenetriamine pentaacetic acid (Gd-DTPA) injection in 12 patients with Q-wave MI supplied by chronically occluded coronary arteries. RESULTS: V(In) from infarct tissue was: 1) higher than V(In) from remote areas (in % of myocardial volume: 74 +/- 16% vs. 20 +/- 7%, P < 0.001); and 2) correlated with the quantification of LCE between infarct and noninfarct areas at the 15th minute (R(2) = 0.63, P = 0.002). However, the difference in V(In) between infarct and remote myocardium was a much better correlate of this quantified LCE (R(2) = 0.85, P < 0.001). CONCLUSION: Detection of LCE in the MI territories supplied by chronically occluded arteries relates to the difference in the V(In) of tracers between the infarct and the noninfarct areas.

Interest of liposomal doxorubicin as a radiosensitizer in malignant glioma xenografts.

Malignant glioma patients have a life expectancy reduced to about 15 months despite aggressive surgery, radiotherapy (RT), and chemotherapy. Doxorubicin has shown a marked cytotoxic effect against malignant glioma cells in vitro. The brain exposure to this drug is, however, hindered by the blood-brain barrier. Encapsulation of doxorubicin in liposomal carriers has been shown to reduce toxicities and to improve brain tumors exposure to doxorubicin. In this study, we evaluated the radiosensitizing properties of a nonpegylated liposomal doxorubicin (Myocet, MYO) on two subcutaneous (U87 and TCG4) and one intracranial (U87) malignant glioma models xenografted on nude mice. Doxorubicin biodistribution was assessed by a high-performance liquid chromatography method. Antitumor efficacy was investigated by tumor volume measurements and mice survival determination. We showed that (i) encapsulation of doxorubicin ensured a preferential deposition of doxorubicin in tumoral tissue in comparison with free doxorubicin; (ii) doxorubicin accumulated in both subcutaneous and intracranial tumors during repeated injections of MYO and this accumulation was linked to the potentiation of RT efficacy on two subcutaneous models; (iii) MYO was unable to improve the antitumoral efficacy of RT on an intracranial glioma model. Finally, this study emphasizes the importance of performing preclinical studies on models closer as possible of human tumors and localization to be more predictive of therapeutic effects observed in humans.

201Tl SPECT abnormalities, documented at rest in dilated cardiomyopathy, are related to a lower than normal myocardial thickness but not to an excess in myocardial wall stress.

UNLABELLED: This study was aimed at determining whether the (201)Tl SPECT abnormalities documented in patients with dilated cardiomyopathy are related to a local excess in wall stress, which might act against the diastolic perfusion of myocardium. METHODS: We included 6 healthy volunteers and 7 patients with idiopathic dilated cardiomyopathy who underwent (201)Tl SPECT at rest. On a 13-segment division of the left ventricle, indices of wall stress and tension were calculated at end-diastole by applying Laplace's law, with thickness and curvature radii being determined for each segment on 2 orthogonal MRI slices. RESULTS: Among all patients, 21 analyzed segments had (201)Tl SPECT defects (D+) and 67 had none (D-). Myocardial thickness was lower in D+ (0.88 +/- 0.30 cm) than in D- (1.23 +/- 0.33 cm, P = 0.0002) or in segments from healthy volunteers (0.99 +/- 0.15 cm, P = 0.04). The index of end-diastolic wall tension was also lower in D+ (2.5 +/- 1.0 N.m(-1).mm Hg(-1)) than in D- (3.3 +/- 1.1 N.m(-1).mm Hg(-1), P = 0.02) or in segments from healthy volunteers (3.2 +/- 1.2 .m(-1).mm Hg(-1)) P = 0.04). Last, the index of end-diastolic wall stress, determined by the ratio of wall tension index to myocardial thickness, was equivalent in D+, in D-, and in segments from healthy volunteers (respectively, 3.0 +/- 1.4, 2.8 +/- 1.2, and 3.2 +/- 1.6 hN.m(-2).mm Hg(-1)). CONCLUSION: In patients with dilated cardiomyopathy, the abnormalities documented by (201)Tl SPECT at rest are related to a lower than normal wall thickness and not to an excess in wall stress or tension. Therefore, partial-volume effects are likely to induce these abnormalities, and they may be unrelated to any insufficiency of myocardial perfusion.