[Delayed myocardial enhancement and diagnosis of acute coronary syndrome with normal coronarography]. / Rehaussement tardif du myocarde et diagnostic étiologique des syndromes coronariens aigus à coronaires saines.

Cardiac MRI in patients with acute coronary syndrome with elevated troponin levels but normal coronarography can now routinely be performed on most MR units. MRI plays an important role in this clinical setting by its ability to detect myocardial infarction in patients with normal coronarography or suggest a different, potentially severe, alternate diagnosis such as myocarditis or takotsubo cardiomyopathy.

Leukoaraiosis and pulse-wave encephalopathy: observations with phase-contrast MRI in mild cognitive impairment.

PURPOSE: To test the pathogenic hypothesis of a breakdown in the vital buffering of the arterial pulsations behind leukoaraiosis (LA) in mild cognitive impairment (MCI). METHODS: Seventy-one elderly patients with MCI underwent a combined structural and dynamic MR examination (3D T1-weighted and fast-FLAIR T2-weighted sequences, phase contrast sequences). Arterial indices of pulsatility (IP) and composite indicators of the amplitude transfer function between cerebrospinal fluid and cerebral venous flow (Icsf/veins) were used to assess the large artery stiffness and the intracranial compliance respectively. Cerebral total arterial blood flow (tCBF), superficial and deep venous flow rates were also measured. Intracranial dynamic parameters and potential confounders including age, gender and vascular risk factors were compared between two groups respectively with and without significant LA. RESULTS: The only dynamic changes on multivariate analyse were an IP increase, a lowering of deep venous outflow and Icsf/veins in patients with LA. There was a significant interaction between IP and Icsf/veins in the logistic regression: as compared with patients with low IP (suggestive of high large artery compliance) and high Icsf/veins (suggestive of high intracranial compliance), the adjusted odds ratios for the presence of LA were 9 (95% CI 1-64, P=0.02) in cases of both high IP and Icsf/veins, 10 (95% CI 1-64, P=0.02) in cases of both high IP and low Icsf/veins and 19 (95% CI 3-127, P=0.002) in cases of both low IP and Icsf/veins. CONCLUSION: LA may reflect an arteriosclerotic and/or resistive pulse wave encephalopathy in MCI.

[Acute abdomen film: is there hope of changing referring patterns?]. / Prescription en urgence d'un abdomen sans préparation: peut-on espérer changer les mauvaises habitudes?

An abdomen radiograph (KUB) is frequently requested by ER physicians as part of the inital work-up of patients. However, other imaging studies are now routinely available in the acute setting that may make the KUB an obsolete and unnecessary examination. The first part of this study was to assess the current referral patterns for urgent KUB in our center; the improper referral pattern for KUB in terms of requests for unnecessary exams 48,5% as well as number of technical errors in terms of inadequate radiographic projection for the suspected pathology 47% were recorded. In a second part, the impact of corrective actions at one month, 2 months and 6 months was assessed and we observed a decrease of about 20% of the number of KUB scheduled by the ER physician. Our results confirm that it is possible to teach ER physicians to more appropriately order imaging studies, which should improve patient care and generate savings. Long term correction of referral patterns is possible if all actors remain involved in this process.

MR imaging of Schmorl's nodes: Imaging characteristics and epidemio-clinical relationships.

PURPOSE: The purpose of our prospective study was to assess the presentation of Schmorl's nodes (SN) on magnetic resonance imaging (MRI) and investigate their possible association with demographic and clinical findings. MATERIALS AND METHODS: Three hundred and thirty-three patients were prospectively included. Thirteen (3.9%) patients were excluded because of contraindication to MRI and/or Scheuermann's disease. The final study population included 320 patients. T1-weighted and short TI inversion recovery sequences were performed to assess SN prevalence, the vertebral level and their anatomical distribution in vertebra. Medical history was recorded focusing on previous diseases including degenerative, rheumatoid and neoplastic disease, and any existing spinal traumatism. Epidemiological information was also obtained, including age, gender, ethnicity, professional and sporting activity. RESULTS: The final study population included 320 patients (172 men, 148 women) with a mean age of 54 years±17.5 (SD) (range: 19-87 years). A total of 421 SN were found in 158/320 patients (49.4%). SN were localized in thoracic spine for 48%, in lumbar spine for 46% and cervical spine for 6%. The middle part of the thoracic vertebra was the most affected area (80%), mostly in the middle superior endplate (41%). SN were more frequently observed in manual workers who worked more than 10 years (P<0.0001) and less frequently in patients of the 30-39-year-old age group (P=0.0048). No significant associations were found with gender (P=0.17) and remarkable medical history (P=0.21). SN were less frequently observed in patients with sport activities of 1-5hours/week (P=0.04) and those with an African origin (P<0.0001). CONCLUSION: Our study suggests a potential role for ethnical and physical factors in the pathogenesis of SN. Furthers studies are mandatory to evaluate their clinical relevance, especially in patients such as Caucasian manual workers in whom SN have a high prevalence.

Assessment of normal values of fractional anisotropy and mean diffusivity of mobile lumbar spine roots by diffuson tensor MRI: comparison between 1.5 and 3T.

PURPOSE: To assess the normal values of fractional anisotropy (FA) and mean diffusivity (MD) of L4, L5 and S1 nerve roots using diffusion tensor imaging (DTI) in healthy volunteers. MATERIALS AND METHODS: 37 subjects without previous history of lumbalgia or radiculalgia were prospectively examined: 27 at 1.5T and 10 at 3T MRI. The protocol included standard anatomical sequences and a DTI acquisition. Nerve root fibers were semi automatically extracted from DTI tractography. FA and MD values were measured at 4 key portions along each L4, L5 and S1 nerve roots. RESULTS: At 1.5T MRI, FA and MD were 0.221 ± 0.011 and 460.9 ± 35.5 mm2.s-1 respectively; at 3T MRI, FA and MD were 0.216 ± 0.01 and 480.1 ± 36.1 mm2.s-1 respectively, which may be considered as normal values for mobile lumbar spine nerve roots, independently of intersomatic space level (p = 0.06) and nerve root portion (p = 0.08) or magnetic field (p = 0.06). CONCLUSION: Normal FA and MD values can be measured along lumbar mobile spine nerve roots in healthy subjects. These values were not dependent on intersomatic space level, side or anatomical portion of the nerve root or magnetic field.

Establishment of diagnostic reference levels in cardiac CT in France: a need for patient dose optimisation.

The objective of this study was to propose diagnostic reference levels (DRLs) for coronary computed tomography angiography (CCTA), in the context of a large variability in patient radiation dose, and the lack of European recommendations. Volume Computed Tomography Dose Index (CTDIvol) and dose-length product (DLP) were collected from 460 CCTAs performed over a 3-month period at eight French hospitals. CCTAs (∼50 per centre) were performed using the routine protocols of the centres, and 64- to 320-detector CT scanners. ECG gating was prospective (n = 199) or retrospective (n = 261). The large gap in dose between these two modes required to propose specific DRLs: 26 and 44 mGy for CTDIvol, and 370 and 970 mGy cm for DLP, respectively. This study confirms the large variability in patient doses during CCTA and underlines the need for the optimisation of cardiac acquisition protocols. Availability of national DRLs should be mandatory in this setting.

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.

Tolerability of hypertonic and isotonic contrast media injected intravenously. A comparative study in the dog.

We examined the use of isotonic and hypertonic contrast media injected intravenously in the dog from the standpoint of cardiovascular tolerance after right atrial injections performed at 2.56 and 5.12 g I/second. The parameters measured were lead II of the electrocardiograph, heart rate, pulmonary and abdominal arterial pressure, and aortic flow. Three contrast media, ioxitalamate, ioxaglate, and iopamidol (two ionic and one nonionic), were compared, either concentrated (32% iodine) or dilute and isotonic with plasma (ioxaglate 160 mg I/mL and iopamidol 128 mg I/mL). At an injection rate of 5.12 g I/second, iopamidol-128 showed lower electrophysiologic tolerability and caused a higher increase in aortic flow than ioxitalamate 160 or ioxaglate 160. These effects may explain the lower radiographic efficacy observed with iopamidol-128 in previous digital subtraction angiography studies.

Hemodynamic effect of iodinated high-viscosity contrast medium in the rat kidney: a diffusion-weighted MRI feasibility study.

RATIONALE AND OBJECTIVES: To assess the abilities of dynamic diffusion-weighted MRI to demonstrate the effects in vivo of a high-viscosity iodinated contrast agent on medullary and cortical blood flow in the rat kidney. METHODS: Dynamic diffusion-weighted, echoplanar MR images obtained from five b-value single-shot acquisitions and their isotropic apparent diffusion coefficient maps were obtained from nine rats anesthetized by pentobarbital sedation, before and after intravenous injection of a high-viscosity, dimeric iso-osmolar iodinated contrast medium (iodixanol), and compared with those obtained from four control rats that received saline. RESULTS: The mean baseline apparent diffusion coefficient values were 1.64 +/- 0.05 x 10(-3) mm2/s for the cortex and 1.75 +/- 0.06 x 10(-3) mm2/s for the medulla. In the iodixanol group, a significant decrease in renal diffusion was observed at 12 minutes and lasted at least until 24 minutes. The decrease in diffusion occurred earlier for the cortex and lasted less than for the medulla. There was no significant modification in diffusion over time in the control group. CONCLUSIONS: This preliminary experience in rats shows that dynamic diffusion-weighted MRI can be used to study noninvasively the in vivo renal hemodynamic response after injection of iodinated contrast.

Study of isotonic contrast media in intravenous digital subtraction angiography.

Arterial enhancement obtained with isotonic contrast media in intravenous digital subtraction angiography was studied. Ten dogs were injected with ioxaglate, iopamidol, and ioxitalamate at equal iodine concentration and at concentrations corresponding to plasma osmolality. Three variables were studied: osmolality, injection rate, and iodine dose. Provided their iodine concentration is sufficient, isotonic contrast media appear as efficient as the corresponding hypertonic formulation, at equal iodine dose. Moreover, the use of isotonic ioxaglate allows a lower dose of iodine to be administered without significant reduction in peak arterial value.

Failing arteriovenous hemodialysis fistulas: assessment with magnetic resonance angiography.

RATIONALE AND OBJECTIVES: The authors sought to evaluate prospectively magnetic resonance angiography (MRA) versus fistulography in the detection and characterization of complications associated with malfunctioning hemodialysis access fistulas (arteriovenous fistulas [AVF]). METHODS: Nineteen patients with clinical AVF dysfunction were studied by MRA and fistulography. Data from each study were collected prospectively and analyzed in a blinded manner. RESULTS: The main diagnosis was stenosis in eight patients, thrombosis in five patients (mural thrombosis with preserved flow in one), aneurysm without stenosis in two patients, and normal AVF in four patients. A hazy flow void, assumed to be related to turbulence, was observed in normal arterial anastomoses. When flow void was considered as a criterion of stenosis or thrombosis, one false-positive and one false-negative MRA study were determined, yielding a sensitivity and specificity of 92% and 86%, respectively. CONCLUSIONS: Magnetic resonance angiography is a feasible and sensitive technique with which to portray suspected malfunctioning hemodialysis access fistulas.

MR imaging of acute spinal cord injury: results of an experimental study in dogs.

A weight-drop model was used to induce 16 acute lesions of varying severity in the spinal cords of eight mongrel dogs. The subsequent 3- to 7-hr postinjury MR images (0.5 T) were assessed. T1-weighted images contributed little information. Injection of gadolinium tetra-azacyclododecane tetraacetic acid did not result in significant enhancement. T2-weighted sequences offered precise detection and delineation of the lesions, displaying fusiform hyperintense signal abnormalities that corresponded to both edema and hemorrhage. In low-impact injuries, abnormalities were small and centrally located, sparing the periphery of the spinal cord. In these cases hemorrhage was minimal and limited to the center of the lesion. In severe-impact injuries, MR showed widespread longitudinal extension with involvement of the periphery of the spinal cord. In the most severe injuries, a central heterogeneous signal component was frequently observed opposite the site of impact because of important hemorrhage within the cord. Overall, hyperintense areas correlated closely with lesion severity, as demonstrated by pathologic findings. T2-weighted MR images obtained at 0.5 T were found to be reliable in the evaluation of acute spinal cord trauma.

Liver positive enhancement after injection of superparamagnetic nanoparticles: respective role of circulating and uptaken particles.

Superparamagnetic nanoparticles have both high r1 and r2 relaxivities responsible for positive or negative enhancement properties. The aim of this study was to investigate to what extent perfusion (circulating particles) and uptake (clustered particles) mechanisms contribute to liver positive or negative enhancement using two different particles, superparamagnetic iron oxides (ferumoxides, AMI 25) and ultrasmall superparamagnetic iron oxides (ferumoxtran, AMI-227). Uptake kinetics were studied after intravenous injection of 20 micromol Fe/kg ferumoxtran on a washout liver model. Livers of 82 rats were surgically isolated and washed with saline infusion. Imaging was performed ex vivo at 0.5T with T1- and T2-weighted sequences. Enhancement kinetics of the liver were studied in vivo using MRI up to 180 min post injection of 20 micromol Fe/kg ferumoxtran (time response study) or 10, 20, 40 micromol Fe/kg ferumoxtran and 20 micromol Fe/kg ferumoxides (dose response study.) Particle uptake occurred early and resulted in a negative enhancement of the washed livers 15 min after injection of both T1 and T2 sequences. In vivo, a positive enhancement was only seen during the first five min with the lowest dose of ultrasmall superparamagnetic iron oxides and the T1 sequence. Uptake and clustering of the particles induced a negative liver enhancement. During the first minutes after injection, when uptake has not significantly occurred, perfusion imaging of the liver at a dose of 10 micromol Fe/kg results in a positive enhancement with T1-weighted sequences.

Superparamagnetic iron oxides as positive MR contrast agents: in vitro and in vivo evidence.

The ability of superparamagnetic iron oxides (SPIO) and ultrasmall superparamagnetic iron oxides (USPIO) to act as positive contrast enhancers due to a marked T1 relaxivity was investigated. At low concentrations, an important signal enhancement was observed in vitro, reaching 120% for SPIO and 140% for USPIO in a spin echo 500/22 sequence. The more heavily the sequence was T1-weighted the greater the enhancement. As the concentration increased, the signal dropped. The in vivo study of USPIO in the rat showed that at low doses (14 mumol Fe/kg), the myocardial signal was enhanced by 30%, whereas at high doses (77 mumol Fe/kg), it fell by -50%. These results indicate that in T1-weighted spin echo sequences, the MR signal can be enhanced by low concentrations of superparamagnetic compounds. This effect could be useful in perfusion imaging, and is also important for a better understanding of any possible paradoxical positive enhancement which could occur in perfused organs.

Temporal and spatial assessment of normal cerebrospinal fluid dynamics with MR imaging.

The purpose of this study was to measure normal cerebrospinal fluid (CSF) pulsations within the intracranial and upper cervical subarachnoid spaces and the ventricular system. Phase contrast cine MR sequences were performed in sagittal and axial planes on 13 volunteers with flow encoding in the craniocaudal direction. CSF pulsations displayed considerable variations in healthy subjects, depending both on measurements localization and subjects, with CSF peak velocities ranging from 0 to 7 cm/s. In the subarachnoid spaces, the highest velocities occurred in the anterior location and increased from the cerebellar pontine angle cisterns towards the lower cervical spaces. In the ventricular system, the highest velocities occurred through the aqueduct of Sylvius. CSF flow within the third ventricle seemed to reflect a circular motion. There was a caudal net CSF flow in the aqueduct whereas in the upper cervical spaces net CSF flow was caudal anteriorly and cranial laterally. Velocity profiles of CSF pulsations demonstrated arterial morphology. After the R wave, caudal systolic motion was first observed in the posterior subarachnoid spaces, soon after in the anterior subarachnoid spaces and later in the ventricular system. Considering the morphology of CSF pathways, three successively initiated phenomena may explain the temporal course of CSF motion: the systolic expansion of the main arteries at the base of the brain, the systolic expansion of the cerebrospinal axis and, finally, the systolic expansion of the choroid plexuses.

Body composition determined with MR in patients with Duchenne muscular dystrophy, spinal muscular atrophy, and normal subjects.

Magnetic resonance imaging was used to determine total fat mass of patients with neuromuscular disorders, accounting for intramuscular fat. Nineteen boys aged 9 to 12 (eight with Duchenne muscular dystrophy, three with type II spinal muscular atrophy and eight control subjects) underwent whole-body magnetic resonance imaging examination and anthropometric measurements. Whole-body fat mass was deduced from automated analysis of images normalized by a reference signal. Intramuscular and subcutaneous fat masses were deduced from manual analysis of twelve reference slices. Affected children significantly differed from control subjects for higher total fat mass, mostly related to intramuscular fat mass. Shorter protocols validated from whole-body data were shown to be more accurate than fat mass estimation derived from anthropometric measurements.

Origin of subarachnoid cerebrospinal fluid pulsations: a phase-contrast MR analysis.

Cerebrospinal fluid (CSF) pulsations result from change of blood volume in the closed craniospinal cavity. We used cine phase contrast MR analysis to determine whether spinal CSF pulsations result from spinal vascular pulsations or intracranial subarachnoid pulsations, whether intracranial CSF pulsations result from intracranial large arteries pulsations or cerebrovascular bed changes. We performed a quantified physiological mapping of CSF velocity waveforms along the craniospinal axis. Thirty-six volunteers participated in the study. MR acquisitions were obtained at the intracranial level, the upper, midcervical, cervicothoracic, mid thoracic, and/or the thoracolumbar levels. The temporal velocity information were plotted as wave form and key temporal parameters were determined and analyzed; intervals from the R wave to the onset of CSF systole, to CSF systolic peak, to the end of systole, as well as duration of systole. Three kinds of dynamic channels could be differentiated along the spinal axis, the lateral, medioventral and mediodorsal channels. Lateral spinal CSF pulse waves show significant craniocaudal propagation. No such significant progression was detected through the medial channels along the spine. Through the medial channels, a cephalic progression was observed from the upper cervical level to the intracranial level. At the craniocervical junction, mediodorsal CSF systole appeared the earliest one whereas in the anterior intracranial basal cistern, CSF systole appeared delayed. In conclusion, spinal CSF pulsations seem to result mainly from intracranial pulsations in the lateral channels, whereas local vascular pulsations could modify CSF pulse wave mainly in the medial channels. At the craniocervical junction, our results suggest that blood volume change in the richly vascularised cerebellar tonsils is the main initiating factor of CSF systole; and that spinal vascular pulsations could be considered as an additional early and variable CSF pump.

MR imaging of coarctation of the aorta and its postoperative complications in adults: assessment with spin-echo and cine-MR imaging.

To evaluate the ability of ECG-gated spin-echo (SE)-MR imaging vs. cine-MR imaging to assess coarctation of the aorta, 11 patients aged 15-45 years, with known or suspected coarctation of the aorta, and five patients suspected of re-stenosis or postoperative false-aneurysms after coarctation repair were examined by multisection SE-MR imaging and single-section multiphase cine-MR imaging on a 1.0 Tesla device. Aortography was performed in 15, and surgery in 14 of these 16 patients. Qualitatively, the location, severity, and length of the coarctation were shown in all cases with MR imaging, as well as the relationship with the arteries arising from the aortic arch. The respective sensitivities and specificities in the assessment of severity of stenoses were 86% and 100% for SE MR images, and 100% and 100% for cine-MR images. Cine-MR imaging was superior to SE imaging in stenosis diameter assessment with contrast angiography as reference, as well as to identify the site of leakage in cases of postoperative pseudoaneurysm. Pre-stenotic dilation or post-stenotic aneurysm, collateral channels, and associated malformations were better identified on SE images. Quantitatively, a better stenosis diameter correlation was found between cine-MR images and angiography than between SE-MR images and angiography (r=0.99 vs. r=0.78; p=0.001 vs. p=0.004), related to overestimation of stenoses with SE-MR imaging. The use of a combination of spin-echo and cine-MR imaging correlates well with conventional angiographic findings in this small series of patients with coarctation of aorta or postoperative pseudoaneurysmal complications. Cine-MRI can provide anatomic information that is equivalent to angiography for surgical planning.

Pulmonary time-of-flight MR angiography at 1.0 T: comparison between 2D and 3D tone acquisitions.

The purpose of this study was to compare the performance of 2D vs. 3D time-of-flight (TOF) methods in imaging the normal pulmonary arteries with commercially available 1.0 T equipment. The study was conducted in 20 volunteers and 7 patients with suspected pulmonary embolism (PE). To reduce artifacts caused by cardiac and respiratory motion, MR images were acquired in volunteers using two-dimensional (2D), gradient-recalled echo (GRE), breath-hold techniques, and three-dimensional (3D) acquisitions. Sagittal thin (6-MM) segmented k-space 2D sections obtained with cardiac gating during systole (turboFLASH, TR/TE9/6 ms, 14 segments of 9 lines) and incremented flip-angles (TONE), and 50-mm 3D volume TONE acquisitions with 32 partitions (FISP, TR/TE34/10ms) were successively performed. In the second phase of the study, patients were examined only with the 3D technique. Images of volunteers were qualitatively and quantitatively analyzed. S/N ratios were statistically compared by means of the paired-sample Wilcoxon ranked-signed test, a value of p < .05 being significant. In volunteers, 3D acquisitions displayed significantly more segment-order pulmonary arteries on average than did 2d acquisitions displayed significantly more segment-order pulmonary arteries on average than did 2D acquisitions (2.95 +/- 0.64 vs. 2.2 +/- 0.85, respectively; p < .01). Moreover, the signal intensity of arteries within the lungs was less homogeneous in the 2D than in the 3D technique, with a signal intensity ratio between peripheral and proximal arteries of 63% +/- 7% and 73% +/- 2%, respectively (p < .05). In patients, no erroneous diagnoses were obtained using the 3D technique. 3D images of normal lungs provide MR angiograms of better quality than do 2D images, and require less contribution from subjects because they are performed in free breathing. Ongoing improvements in MR sequences and further studies are now necessary to assess the value of 3D TONE MRA in the diagnosis of PE.

Screening of renal artery stenosis: assessment with magnetic resonance angiography at 1.0 T.

The results of MR angiography at 1.0 T with digital intraarterial angiography in the screening of patients with suspected renal hypertension were compared. In this first phase of the study, 10 volunteers underwent examination with both two-dimensional (2D) with traveling saturation time-of-flight (TOF) magnetic resonance angiography (MRA) with various parameters to develop a protocol for evaluation of the renal arteries. In the second phase, 36 patients with suspected renovascular hypertension underwent both 2D TOF MRA and intraarterial digital angiography to evaluate the clinical value of MRA. The degree of stenosis was graded with a two-point scale. In volunteers, using 2D acquisitions C/N ratios indicated the best flip angle as being 55 degrees (p = .02). MRA showed 100% (70/70) of all main arteries and 86% (6/7) of all accessory renal arteries seen on angiography. MRA had a sensitivity of 94% (15/16) and a specificity of 98% (60/61) for detection of stenoses of greater than 50% present in 14 patients. 2D-TOF MRA at 1.0 T shows promise in the noninvasive diagnosis of patients with suspected renovascular hypertension.