[Mechanisms of delayed myocardial enhancement and value of MR and CT contrast materials in the evaluation of myocardial viability]. / Mécanismes du rehaussement tardif myocardique et apport des produits de contraste en IRM et scanner dans le diagnostic de viabilité myocardique.

The purpose of this article is to present a brief theoretical review of the models characterizing delayed myocardial enhancement applicable to both MR and CT imaging, review the different characteristics of commercially available gadolinium-based and iodinated contrast materials, and summarize the literature on the potential value of dedicated MR imaging contrast currently in development for the diagnosis of myocardial viability. The intensity of myocardial enhancement following infarction is related to two factors: expansion of the interstitial volume (15+/-2% in normal myocardium and 80+/-3% within necrosis) secondary to cell necrosis and perfusion abnormalities due to the absence of revascularization or lesions to the microcirculation. A kinetic model of contrast material properties within myocardium could be constructed from Kety's equation with regards to enhancement within the different myocardial tissues (viable myocardium, necrotic myocardium, fibrosis, no-reflow zones, stunned or hibernating myocardium). This model can be applied to both CT and MR since clinically available contrast agents are extracellular, inert and kinetically comparable. The development of dedicated contrast agents for viability and necrosis or molecular contrast agents open new horizons for preclinical research.

Comparison of the angiographic myocardial blush grade with delayed-enhanced cardiac magnetic resonance for the assessment of microvascular obstruction in acute myocardial infarctions.

BACKGROUND: Both myocardial blush grade (MBG) and cardiac magnetic resonance (CMR) are imaging tools that can assess myocardial reperfusion after primary percutaneous coronary intervention (PCI) for acute myocardial infarction (AMI). OBJECTIVES: We studied the relation between MBG and gadolinium-enhanced CMR for the assessment of microvascular obstruction (MVO) in patients with acute ST-elevated myocardial infarction (STEMI) treated by primary PCI. MATERIAL AND METHODS: MBG was assessed in 39 patients with initial TIMI 0 STEMI successfully treated by PCI, resulting in TIMI 3 flow grade and complete ST-segment resolution. These MBG values were related to MVO determined by CMR, performed between 2 and 7 days after PCI. Left ventricular (LV) volumes were determined at baseline and at 6-month follow-up. RESULTS: No statistical relation was found between MBG and MVO extent at CMR (P = 0.63). Regarding MBG 0 and 1 as a sign of MVO, the sensitivity and specificity of these scores were 53.8 and 75%, respectively. In this study, CMR determined MVO was the only significant LV remodeling predicting factor (beta = 31.8; P = 0.002), whatever the MBG status was. CONCLUSION: MBG underestimates MVO after an optimal revascularization in AMI compared with CMR. This study suggests the superior accuracy of delayed-enhanced magnetic resonance over MBG for the assessment of myocardial reperfusion injury that is needed in clinical trials, where the principal endpoint is the reduction of infarct size and MVO.

Presence and extent of cardiac magnetic resonance microvascular obstruction in reperfused non-ST-elevated myocardial infarction and correlation with infarct size and myocardial enzyme release.

OBJECTIVE: Microvascular obstruction (MO) is a factor of adverse outcome in patients with ST-elevated myocardial infarction (STEMI). We assessed the presence and extent of MO and its relationship with infarct size and left ventricular (LV) functional parameters after acute non-ST-elevated myocardial infarction (NSTEMI). METHODS: Twenty-five patients with first acute NSTEMI underwent a cine and first-pass perfusion cardiac magnetic resonance (CMR) study, with late gadolinium enhancement imaging 72 h after myocardial infarction. RESULTS: MO was detected in 32% of patients, and its extent comprised 0.5-3.1% of the total LV mass (mean 1.9 +/- 1.2%). Patients with MO had a significantly larger infarct size than patients without (14.1 +/- 5.9 vs. 5.3 +/- 4.1% LV mass; p < 0.001). There was no significant difference between both groups for the LV functional parameters and LV ejection fraction (58.5 +/- 6.8 vs. 62.6 +/- 9.6%; p = 0.29). Patients with MO showed a higher troponin I release (570 +/- 364 vs. 148 +/- 103 IU; p = 0.003) and a higher creatine kinase release (29,887 +/- 18,263 vs. 10,287 +/- 5,283 IU; p = 0.007). CONCLUSIONS: In patients with acute NSTEMI, MO has a frequency similar to that observed in patients with STEMI and also correlates with the infarct extent. The prognostic significance on clinical outcome remains to be shown in this specific population.

[Current indications for cardiac MR imaging]. / Indications cliniques appropriées de l'IRM en pathologie cardio-vasculaire.

MRI has acquired over the years a role in the evaluation of cardiovascular pathology especially with regards to its ability to assess right and left ventricular function and delayed postcontrast "viability" sequences. Current class I clinical indications include: viability for patients with ischemic cardiomyopathy and acute coronary syndrome, etiology and prognostic evaluation of non-ischemic cardiomyopathies including myocarditis and arrhytmogenic right ventricular cardiomyopathy, chronic pericarditis and cardiac masses, non-urgent aortic aneurysm and dissection, congenital cardiopathies: vascular malformations and follow-up after curative or palliative surgery. MRI provides a complete non operator dependent evaluation, and is particularly useful for follow-up since it may be repeated due to its absence of ionizing radiation

Endovascular repair of the descending thoracic aorta: mid-term results and evaluation of magnetic resonance angiography.

AIM: The endoluminal stent-grafting represents an alternative to surgery in the treatment of lesions of the descending thoracic aorta. The purpose of the present study was to evaluate the mid-term results of the Talent stent-graft in the different indications of aortic disease and the use of magnetic resonance angiography (MRA) in the diagnosis of complications. METHODS: Over a 3-year period, 23 patients with a high surgical risk and presenting a localized lesion of the descending thoracic aorta had an implantation of a Talent stent-graft. Indications were degenerative aneurysm (n=13), false aneurysm (n=7) and penetrating atherosclerotic ulcer (n=3). The feasibility of the endovascular treatment and sizing of the aorta and stent-grafts were determined pre-operatively by MRA and intraoperative angiography. Immediate and mid-term technical and clinical success were assessed by clinical and MRA follow-up. RESULTS: Endovascular treatment was completed successfully in all patients with no conversion to open repair. There was no intraoperative mortality. The mean operative time was 38+/-7 min. Primary success rate was 100%. We didn't have perioperative mortality. The mean follow-up period was 15+/-5 months. The survival rate was 97% (n=22). Regression of the aneurysmal size was observed in 70% (n=16). MRA diagnosed 3 over 4 postoperative endoleaks that were not diagnosed with the CT-scan, and did not interfere with the nitinol structure of the stent-graft. CONCLUSIONS: Endovascular treatment of the various localized diseases of the descending thoracic aorta is a promising, feasible, alternative technique to open surgery in well selected patients. MRA is well adapted to diagnose postoperative endoleaks.

[Cardiac CT: What role should it play in coronary artery disease?]. / Scanner cardiaque: quelle place dans la maladie coronaire?

The recent developments in the multi-slice CT scanner require evaluation of the clinical indications of this new tool for imaging coronary arteries. Improvements in spatial and temporal resolution with this new generation of CT (16 slices and more) allow the acquisition of coronary arteries with a sufficient quality in the majority of cases. After a short review of the technical principles of the cardiac CT, this article considers the clinical indications of this new method in the general evaluation of coronary artery disease.

MR imaging assessment of myocardial edema with T2 mapping.

Cardiac magnetic resonance (CMR) provides a high signal-to-noise ratio, high spatial and temporal resolutions, as well as a delayed-enhancement sequence and is therefore considered a reference technique in the field of cardiac imaging. However, currently available sequences are not adequate to assess some pathologic conditions, such as myocardial edema. T2 mapping sequences generate parametric images that are based on the transverse relaxation time (T2) for each voxel. In case of edema, the T2 relaxation time is longer. This review summarizes current knowledge on CMR T2 mapping for assessing myocardial edema.

[Emergent transcatheter aortic valve implantation in a patient with bicuspid aortic valve stenosis in cardiogenic shock]. / Choc cardiogénique sur bicuspidie aortique sténosante traité par remplacement valvulaire aortique percutané en urgence.

Transcatheter aortic valve implantation is a therapeutic option for high-risk patients with severe aortic valve stenosis and with cardiac symptoms. This procedure requires the preliminary evaluation by a "heart team" and presents some contraindications. We report the case of a 58-year-old man with severe bicuspid aortic valve stenosis and cardiogenic shock. In spite of contraindications and because of the failure of balloon aortic valvuloplasty, transcatheter aortic valve implantation was performed in emergency.

Early events in the experimental interstitial lung disease induced in sheep by the Visna-maedi virus.

Visna-maedi virus is a lentivirus closely related to the human immunodeficiency virus type I (HIV-I). During spontaneous infection of sheep by Visna-maedi virus an interstitial lung disease is observed. It is characterized by an alveolitis, peribronchovascular lymphoid nodules, alveolar wall thickening and myomatosis. In order to decipher the pathology of this lentiviral infection we have induced this disease in colostrum-deprived newborn lambs.

High-resolution computed tomographic findings associated with histologically diagnosed acute lung rejection in heart-lung transplant recipients.

A group of 32 lung (single lung, [n = 14] and double lung [n = 1]) or heart-lung (n = 17) transplant recipients were studied with serial high-resolution computed tomography (HRCT) scans and transbronchial biopsies from the time of surgery. These investigations were carried out routinely every 2 weeks for the first 2 months, every 2 months for a year, every 4 months in the second year, and on any clinical suspicion of acute lung rejection or infection. A total of 190 transbronchial biopsy specimens and concurrent HRCT scans were obtained. Forty (21%) of the biopsy specimens, showed histologic evidence of lung rejection, 111 (58%) were normal, and 39 (21%) were not conclusive. The more frequent HRCT pattern encountered during an acute rejection episode was the presence of patchy "ground-glass" density areas (65%). This finding was sparsely observed during minimal and mild acute rejection episodes. Using histologic diagnosis as a standard for acute rejection, ground-glass opacities on HRCT had a sensitivity of 65% in detecting lung rejection. Although ground-glass opacities were also intermittently observed during cytomegalovirus pneumonia (14%), this finding had a specificity of 85% for detecting occurrence of an acute lung complication. The detection of ground-glass opacities on lung HRCT after lung transplantation, more particularly after the first month after surgery, can aid the decision of when and where to undertake transbronchial lung biopsy.

Thin-section CT detection of emphysema associated with bronchiectasis and correlation with pulmonary function tests.

PURPOSE: To evaluate, on thin-section CT scans, the prevalence of emphysema in patients with bronchiectasis and to correlate the results of thin-section CT scans with the results of pulmonary function tests, in order to question whether there was a particular functional test profile in this group of patients. PATIENTS AND METHODS: This is a retrospective study including 90 patients having both thin-section CT scans and pulmonary function tests for bronchiectasis. A CT scoring system was established for assessing the airway disease by the severity and extent of bronchiectasis and by the extent of emphysema. CT scans were reviewed independently by two reviewers and final interpretation was obtained by consensus. Results of thin-section CT scans were correlated with results of pulmonary function tests, including FEV1 and FEV1/FVC to assess air-way obstruction, total lung capacity and residual volume to assess air trapping, and diffusing capacity for carbon monoxide/alveolar volume (DCO/VA). RESULTS: CT evidence of emphysema, which was noted in 45% of the patients (n = 41), was mainly localized in the same bronchopulmonary segments as bronchiectasis. The presence of emphysema was in relation to the extent and to the severity of bronchiectasis. Only eight patients with CT evidence of emphysema had functional evidence of emphysema (20%). When comparing the group of patients with CT evidence of emphysema with the group of patients with no CT evidence of emphysema, the group of patients with CT evidence of emphysema had significantly higher airflow obstruction and air trapping, had significantly lesser value of diffusing capacity, but with no decreased gas transfer (DCO/VA > 80%). CONCLUSION: Our series suggests that there is a high prevalence of emphysema in patients with bronchiectasis. Emphysema that was not suggested using pulmonary function tests in most of the cases could explain in part the higher airway obstruction observed in the group of patients with CT evidence of emphysema. This study could support the suggestive notion that emphysema, which was mainly localized in bronchiectatic lobes, could be due to the inflammatory airway process.

Metalloporphyrin contrast enhancement of tumors in magnetic resonance imaging. A study of human carcinoma, lymphoma, and fibrosarcoma in mice.

The diagnostic use of Mn(III)TPPS4, a paramagnetic metalloporphyrin, for MR contrast enhancement was examined in human--mouse xenograph models of carcinoma, lymphoma, and sarcoma. Spin-echo images of 15 mice, five mice for each implanted tumor type, were obtained before and at 20 minutes, and 2, 4, and 24 hours following administration of 0.09 mmol/kg of Mn(III)TPPS4. All tumors had a uniform moderate signal intensity on precontrast images. After administration of Mn(III)TPPS4, all tumors demonstrated significant enhancement of signal intensity that persisted to 24 hours. T1 relaxation times were maximally depressed at 2-4 hours and remained low to 24 hours for all three tumors. Kidney signal intensity reached a maximum at 20 minutes and remained significantly above background for 24 hours. The high relaxivity and apparent avidity of Mn(III)TPPS4 for divergent tumor histologies support the potential use of this agent for improved diagnostic specificity of MR imaging for neoplastic masses.

Fusion of cine magnetic resonance and contrast-enhanced first-pass magnetic resonance data in patients with coronary artery disease: a feasibility study.

RATIONALE AND OBJECTIVES: The left ventricle (LV) myocardial wall contractibility can be evaluated using cine magnetic resonance imaging (MRI) in a qualitative or quantitative manner. Meanwhile, myocardial perfusion can be assessed using contrast-enhanced first-pass MRI. The authors propose a method of automatically fusing the complementary information from these two cardiac MRI modalities into one single image, from which a match or mismatch between contraction and perfusion could be extracted. METHODS: The authors developed a registration algorithm based on the combined use of the global affine transformation and intrinsic landmarks to match images from the same sequence or from two imaging sequences. Contraction and perfusion information was fused by combining a myocardial contour image and a parametric image of the slope of the intensity-time curve, respectively. The fusion paradigm was applied to four patients' data as a demonstration of feasibility of the proposed approach and as a preliminary evaluation. RESULTS: Cine MR and contrast-enhanced MR images were well aligned. The contractibility of the LV was displayed by the myocardial contour image. The parametric slope image was consistent with the known coronary artery status of each patient. The combined contraction-perfusion representation of the LV showed the correspondence between regional LV contraction and myocardial perfusion at a one slice level. CONCLUSIONS: Left ventricle contraction and myocardial perfusion can be represented conjointly in one single fused image. The fusion paradigm should be evaluated for a larger number of patients to evaluate the clinical relevance of this approach in assessing coronary artery disease.

Canine acute myocardial infarction. In vivo detection by MRI with gradient echo technique and contribution of Gd-DOTA.

This experimental study was designed to evaluate the sensitivity of MRI in the detection of acute myocardial infarction, determine the utility of fast gradient-echo (GE) imaging and study possible improvements in diagnostic efficacy using a paramagnetic contrast agent (gadolinium-DOTA). Myocardial infarcts were induced in 11 dogs by semidistal embolization and imaged using spin-echo and/or GE pulse sequences, short TRs (250 to 450 ms) and cardiac gating. After the dogs died, the heart was imaged under the same conditions as in vivo. Blind comparisons between precontrast, postcontrast (0.1 mM/kg and 0.5 mM/kg), postmortem images and anatomic findings (triphenyl-tetrazolium-chloride staining) were recorded. This study shows that infarcted areas can be detected on plain MRI images in the form of a hypersignal, probably attributable to increased proton density, with better efficiency of GE compared with spin-echo imaging; injection of gadolinium-DOTA allows better delineation of infarcted areas, especially for 10 minutes after administration.

Magnetic resonance imaging of experimental renal hemorrhage.

Experimental renal hemorrhage was induced by injecting autologous blood into the left kidney of 13 rats. To investigate the magnetic resonance (MR) characteristics of acute renal hemorrhage and subsequent stages of resolution, repetitive MR images were obtained using a 0.35 Tesla imager during a period of 21 days postinduction. A dual spin-echo imaging (TR 500 and 2,000 msec, TE 28 and 56 msec) was used to calculate the relaxation times and record the intensities in the renal medulla and cortex. Histologic examination (n = 9) indicated that blood was dispersed intrarenally, and no encapsulated hematoma developed. The signal intensity on the T1- and T2-weighted images, as well as the relaxation times in the hemorrhagic renal parenchyma were unchanged during 21 days when compared with intact kidney values. Subcapsular fresh blood had a high signal intensity on T2-weighted images. A marked overlap of the relaxation parameters between intact kidney parenchyma and diffuse intrarenal hemorrhage was observed. Detection of dispersed intrarenal blood using spin echo MR imaging may be difficult.

Lung perfusion demonstrated by contrast-enhanced dynamic magnetic resonance imaging. Application to unilateral lung transplantation.

RATIONALE AND OBJECTIVES: The authors evaluate the use of magnetic resonance (MR) to image pulmonary perfusion in healthy controls and to detect pulmonary defects in patients with unilateral lung transplantation, using dynamic images after contrast administration. METHODS: Five patients with right lung transplantation and nine healthy volunteers underwent MR imaging. Twenty-five subsecond contrast-enhanced MR images (turbo-fast low-angle shot [FLASH]) were obtained at the level of the pulmonary arteries after a single injection of gadopentetate dimeglumine (0.1 mmol/kg) in an antecubital vein. Perfusion lung scintigraphy was done within 24 hours after the MR imaging examination in the transplanted patients. RESULTS: Before administration of contrast material, MR images showed both lungs to be homogeneous and of low signal intensity in healthy controls and in patients with lung transplantation. After contrast administration in controls, the mean signal intensity of the dependent lung increased markedly to 171 +/- 24% above baseline, whereas the nondependent signal intensity lung increased by only 105 +/- 17%; these changes were significantly different. In all patients with lung transplantation, a clear perfusion defect was demonstrated in the native lung. This defect was confirmed in all cases by perfusion nuclear scintigraphy, which showed that the majority of lung perfusion is directed to the transplanted allograft, compared with the native contralateral lung. CONCLUSIONS: Our results suggest that dynamic contrast-enhanced MR imaging is a potential method for detecting pulmonary perfusion defects in patients with lung transplantation.

Carboxymethyl-dextran-gadolinium-DTPA as a blood-pool contrast agent for magnetic resonance angiography. Experimental study in rabbits.

RATIONALE AND OBJECTIVES: The authors evaluate the efficiency of various doses of a paramagnetic macromolecular contrast agent, a gadolinium (Gd)-DTPA-dextran conjugate, as a blood-pool contrast media, in a transverse three-dimensional time-of-flight (TOF) magnetic resonance (MR) angiography sequence of the abdominal aorta in rabbits. METHODS: Imaging experiments were performed on a 1.5-T magnet, using a transverse three-dimensional TOF tilted optimized nonsaturating excitation (TONE) sequence. The macromolecular contrast media used was a carboxymethyl-dextran-Gd-DTPA (CMD-Gd-DTPA). Different concentrations of CMD-Gd-DTPA (0.005, 0.01, 0.03, 0.05 mmol Gd/kg) were evaluated. A comparative study using Gd-DOTA (0.01 and 0.1 mmol/kg) was performed. A visual analysis based on the gain in the visualized length of small arteries (renal arteries), and a quantitative analysis based on the percent contrast enhancement of the aorta plotted against distance in the slab from the top edge of the acquisition volume were obtained. RESULTS: A signal-to-noise ratio enhancement of the distal part of the aorta and an improvement in the visualized length of the renal arteries were noted for concentrations of CMD-Gd-DTPA ranging form 0.01 to 0.05 mmol Gd/kg. Venous enhancement was noted for concentrations greater than 0.01 mmol Gd/kg when using CMD-Gd-DTPA or Gd-DOTA. CONCLUSION: Carboxymethyl-dextran-Gd-DTPA reduced, in part, the saturation effect in a three-dimensional transverse TOF TONE MR angiography in rabbits. To prevent venous enhancement, observed with the higher concentrations used in this study, a decrease in the polydispersity of the polymer should be a goal in the future. Rapid extravasation of the low-molecular weight fraction of the polymer could explain the venous enhancement.

Magnetic resonance imaging in the diagnosis of acute renal allograft rejection and its differentiation from acute tubular necrosis. Experimental study in the dog.

This study was designed to evaluate the potential utility of magnetic resonance imaging (MRI) for the diagnosis of acute renal allograft rejection and its differentiation from acute tubular necrosis (ATN). Eighteen canines were used. Five animals served as controls. ATN was induced in six animals by cross-clamping of the left renal artery for 90 minutes. In order to study acute renal allograft rejection, seven animals were subjected to exchange allograft transplantation of the left kidney. MRI was performed with a 0.35T superconductive magnet. A double spin-echo technique was used with varying TR and TE parameters. The spin echo images were analyzed for morphology, signal intensity, T1 and T2 relaxation times, and spin density. The most useful MRI criteria for the diagnosis of ATN and acute rejection were found to be the renal size, the intensity difference between cortex and medulla (corticomedullary contrast), and the T1 relaxation time of the cortex. Normal kidneys showed maximal corticomedullary contrast (19% +/-2) on images obtained with TR = 0.5 sec and TE = 28 msec. Cortical T1 relaxation time was 551 msec + /-73. In the ATN group, the kidneys were slightly swollen (P = ns) and the corticomedullary contrast (11% + /-3) was reduced by 42% (P less than .01). T1 of the cortex (689 + /-142) was increased by 25% (P less than .10). In acute rejection, significant renal enlargement was noted (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Predictive value of regional left ventricular circumferential shortening in jeopardized myocardium. A two-dimensional SPAMM cine-MRI study in a canine model.

OBJECTIVE: To determine whether myocardial circumferential shortening assessed in the different myocardial layers by SPAMM cine-MRI may help to discriminate between various degrees of myocardial injury in reperfused myocardium. METHODS: Dogs underwent 90 minutes of coronary occlusion and 24 hours of reperfusion. Using a 1.5 T whole-body MR scanner, SPAMM cine-MRI images were acquired before and 24 hours after surgery on the short axis plan of the left ventricle and analyzed to evaluate the mean myocardial circumferential shortening (% MCS) in the different layers. Based on the residual blood flow, animals were assigned to group I (residual flow < 22.5%) or group II (residual flow > 22.5%). RESULTS: Dogs in group I developed larger infarctions (25.3% +/- 14.6 of the area at risk, n = 5) compared with those in group II (5.81% +/- 1.1, n = 7, P < 0.05). In the jeopardized zone, the % MCS of the subendocardium decreased more significantly in group I (-0.03% +/- 3.7 to 2.2% +/- 5.2) compared with group II (14.7% +/- 1.5 to 18.4% +/- 1.4). CONCLUSIONS: SPAMM cine-MRI is a fast and noninvasive means of measuring % MCS. The MR measurement of this parameter in the subendocardial layer appears quite accurate in describing the degree of damage in reperfused myocardium.