Marfan syndrome: evaluation with MR imaging versus CT

Twenty-five patients with Marfan syndrome underwent computed tomography (CT) and magnetic resonance (MR) imaging. MR images were interpreted in blinded fashion and then the results were compared with findings from CT scans. MR imaging was found to be equivalent to CT in the depiction of aortic, dural, and hip abnormalities in patients who had not undergone surgery. MR imaging was superior to CT in evaluation of postoperative patients because the artifact produced by Bjork-Shiley or St. Jude valves precludes adequate evaluation of the aortic root on CT scans, while producing only a small inferior field distortion, a "pseudo-ventricular septal defect," on MR images. The absence of radiation exposure is another significant advantage for the relatively young Marfan syndrome population, who require serial studies. MR imaging is the modality of choice for evaluation and follow-up of patients with Marfan syndrome and offers an appropriate means of screening their kindred.     

MR imaging of the thoracic aorta in Marfan patients

A characteristic shape of the ascending aorta has been reported in patients with Marfan syndrome. To evaluate the capability of magnetic resonance (MR) imaging to distinguish between marfanoid and other aortic aneurysms, 11 Marfan patients (group 1), eight patients with ascending aorta enlargement (group 2), and 20 normal subjects (group 3) had transverse and sagittal MR of the thoracic aorta. Aortic diameter was measured at the sinuses of Valsalva (SV), the caudal portion of the ascending aorta, the prearch region (PA), the middle arch, and the descending aorta. The ratio SV/PA was significantly greater (p less than 0.001) in group 1 compared with groups 2 and 3. The SV/PA in all Marfan patients exceeded 1.4 but was less than 1.3 in subjects of groups 2 and 3. Magnetic resonance imaging provides definitive measurements of aortic dimensions and is potentially the method of choice for establishing the diagnosis of aortic involvement in Marfan syndrome and monitoring the course of aortic enlargement.     

Blood flow measurements in the aorta and major arteries with MR velocity mapping

The purpose of this study was to measure antegrade and retrograde flow in the aorta and the major arterial pathways in the body noninvasively with cine magnetic resonance (MR) velocity mapping, to determine the hemodynamic significance of retrograde flow in arteries. Two hundred forty cine velocity maps for blood flow measurements were obtained at 29 sites in the aorta and the major arteries in 31 healthy human subjects of varying age at rest. Synchronous or isolated antegrade and retrograde flow was found in the entire aorta and in arteries supplying muscles. No retrograde flow was found in arteries supplying internal organs, such as the internal carotid or splanchnic arteries. The retrograde flow in the aorta and the extremity arteries contributes substantially to supplying diastolic perfusion of internal organs such as the heart, brain, and kidneys. Antegrade flow tends to be helical in the thoracic aorta.     

Vein graft function improvement after percutaneous intervention: evaluation with MR flow mapping

PURPOSE: To provide functional reference values in single and sequential vein grafts by using magnetic resonance (MR) flow mapping and to examine the effect of percutaneous intervention (PCI) on coronary artery bypass graft function. MATERIALS AND METHODS: Fast MR flow mapping at baseline and during adenosine-induced stress was performed in 39 nonstenotic single vein grafts and 20 nonstenotic sequential vein grafts, as well as in 15 stenotic vein grafts before and 7.3 weeks +/- 1.5 after successful PCI. We evaluated the following parameters (in terms of mean values +/- SDs): average peak velocity (APV) at baseline, stress APV, and velocity reserve. Parameters in nonstenotic single and sequential vein grafts were compared by means of unpaired two-tailed Student t testing. To evaluate changes in velocities before and after PCI, a paired two-tailed Student t test was used. P <.05 was considered to indicate a statistically significant difference. RESULTS: Reference values in single vein grafts for baseline APV, stress APV, and velocity reserve were 8.6 cm/sec +/- 3.4, 20.2 cm/sec +/- 9.5, and 2.4 +/- 0.8, respectively. In sequential vein grafts, significantly higher values for baseline APV (12.2 cm/sec +/- 5.0) and stress APV (27.2 cm/sec +/- 10.6) but a similar velocity reserve (2.3 +/- 0.7) were found. Significant improvements were observed after PCI in baseline APV (before PCI: 9.2 cm/sec +/- 6.6; after PCI: 12.9 cm/sec +/- 7.9; P =.008) and stress APV (before PCI: 12.9 cm/sec +/- 6.3; after PCI: 27.1 cm/sec +/- 13.9; P <.001). No improvement in velocity reserve was observed. CONCLUSION: Significantly higher absolute velocity and flow values were observed in sequential versus single vein grafts, underscoring the need for separate functional reference values for different graft types. Graft function showed significant improvement after PCI to the point that it was restored or nearly restored to reference values.     

Aortic flow patterns in patients with Marfan syndrome assessed by flow-sensitive four-dimensional MRI

Purpose:

To apply time‐resolved three‐dimensional (3D) phase contrast MRI with three‐directional velocity encoding (flow‐sensitive 4D MRI) for the characterization of flow pattern changes in patients with Marfan syndrome (MFS) compared with normal controls.

Materials and Methods:

Flow‐sensitive 4D MRI of the thoracic aorta (temporal resolution ～45 ms, spatial resolution ～2.4 × 2.1 × 2.8 mm³) was performed in 24 MFS patients and 10 volunteers. Aortic flow patterns were visualized by 3D particle traces and streamlines. Global (affecting the complete lumen) and local (parts of the vessel lumen) helix and vortex flow in the ascending aorta (AAo), aortic arch, and descending aorta (DAo) were graded in 3 categories (blinded reading, two observers): none = 0, moderate = 1, pronounced = 2.

Results:

Flow grading revealed similar global helix and vortex flow in the AAo and arch for MFS patients and controls. Local helix flow in the AAo was significantly (P = 0.011) increased in patients and was associated with aortic sinus dilatation. The incidence of global helix and vortex flow in the DAo was increased in patients (77% and 50% of subjects) compared with controls (none and 10%).

Conclusion:

The 4D flow analysis revealed marked differences of the aortic flow patterns between Marfan patients and controls: Local helix flow in the patients' AAo may be associated with the increased incidence of aortic root dilatation. The flow alterations in the proximal DAo could explain the occurrence of Type‐B dissection originating from this site. J. Magn. Reson. Imaging 2012;35:594‐600. © 2011 Wiley Periodicals, Inc.     

Blood flow patterns in the thoracic aorta studied with three-directional MR velocity mapping: The effects of age and coronary artery disease

The objective was to investigate how the blood flows in the thoracic aorta, with special emphasis on flow reversal and flow into the coronary arteries. Three-directional MR velocity mapping was used to map multidirectional flow velocities in the aorta in 14 normal subjects and 14 patients with coronary artery disease. Dynamic flow vector maps and through-plane velocity maps were used. The flow reversed in all subjects in the upper ascending aorta and usually also in the distal aortic arch. Retrograde flow became antegrade again at various levels in the ascending aorta and in the coronary sinuses. Seven flow characteristics were investigated that, lumped together, were significantly different (P = .0005) in normal subjects compared with patients and in normal subjects 70 years of age and older compared with those younger than 70 years of age.     

Vena caval flow: assessment with cine MR velocity mapping

The authors used cine magnetic resonance (MR) velocity mapping to study flow in the superior vena cava (SVC) and inferior vena cava (IVC) of 13 healthy control subjects and 13 patients with right-sided cardiac disease. In the control subjects, peaks of flow in systole and diastole were observed, and mean SVC flow was 35% of the cardiac output. Respiratory gating was used in six control subjects to acquire images at end inspiration and end expiration, and although the systolic peak was reduced at end expiration, total flow was unchanged. A reduced systolic peak and retrograde flow in the IVC were observed in patients with tricuspid regurgitation. A reduced diastolic peak was seen in patients with pulmonary hypertension, pericardial constriction, and right ventricular dysplasia, reflecting reduced diastolic compliance of the right ventricle. In the patient with obstruction of the SVC, absence of flow was confirmed, and retrograde flow was seen in the azygos vein. The authors believe that cine MR velocity mapping is a reliable method of studying vena caval flow noninvasively and that it has important potential applications for the investigation of disorders of the right side of the heart.     

Accelerated time-resolved three-dimensional MR velocity mapping of blood flow patterns in the aorta using SENSE and k-t BLAST

Purpose

To assess the feasibility and potential limitations of the acceleration techniques SENSE and k-t BLAST for time-resolved three-dimensional (3D) velocity mapping of aortic blood flow. Furthermore, to quantify differences in peak velocity versus heart phase curves.

Materials and methods

Time-resolved 3D blood flow patterns were investigated in eleven volunteers and two patients suffering from aortic diseases with accelerated PC-MR sequences either in combination with SENSE (R = 2) or k-t BLAST (6-fold). Both sequences showed similar data acquisition times and hence acceleration efficiency. Flow-field streamlines were calculated and visualized using the GTFlow software tool in order to reconstruct 3D aortic blood flow patterns. Differences between the peak velocities from single-slice PC-MRI experiments using SENSE 2 and k-t BLAST 6 were calculated for the whole cardiac cycle and averaged for all volunteers.

Results

Reconstruction of 3D flow patterns in volunteers revealed attenuations in blood flow dynamics for k-t BLAST 6 compared to SENSE 2 in terms of 3D streamlines showing fewer and less distinct vortices and reduction in peak velocity, which is caused by temporal blurring. Solely by time-resolved 3D MR velocity mapping in combination with SENSE detected pathologic blood flow patterns in patients with aortic diseases. For volunteers, we found a broadening and flattering of the peak velocity versus heart phase diagram between the two acceleration techniques, which is an evidence for the temporal blurring of the k-t BLAST approach.

Conclusion

We demonstrated the feasibility of SENSE and detected potential limitations of k-t BLAST when used for time-resolved 3D velocity mapping. The effects of higher k-t BLAST acceleration factors have to be considered for application in 3D velocity mapping.     

MR evaluation of dural ectasia in Marfan syndrome: reassessment of the established criteria in children, adolescents, and young adults

PURPOSE: To retrospectively evaluate known criteria for assessment of dural ectasia by using magnetic resonance (MR) imaging in children, adolescents, and young adults with and those without Marfan syndrome. MATERIALS AND METHODS: Local ethics committee approval and informed consent were obtained. MR images of the lumbar spine in 28 patients with clinically proved Marfan syndrome (group A; 17 male, 11 female; age range, 4-21 years; mean, 12.1 years), seven patients with suspicion of Marfan syndrome (group B; six male, one female; age range, 6-18 years; mean, 10.4 years), and 55 patients without Marfan syndrome (group C; 26 male, 29 female; age range, 4-20 years; mean, 10.7 years) were evaluated retrospectively for dural ectasia criteria (scalloping, dural sac ratio, nerve root sleeve diameter, sagittal dural sac width at S1 greater than that at L4) and according to classifications by Ahn et al and Fattori et al. For statistical comparison of results, one-way analysis of variance with Scheffe post hoc comparisons was used, with an overall two-tailed significance at alpha = .05. RESULTS: No significant differences in scalloping and nerve root sleeve diameter were shown between groups. A significant difference was measured for dural sac ratios at L5 and S1 (F test, P = .003 and P < .001 at L5 and S1, respectively; post hoc t test for groups A vs C, P = .004 and P < .001 at L5 and S1, respectively). Significant differences were also obtained between groups A and C for sagittal dural sac width at S1 greater than that at L4 according to the calculated mean difference (for both F test and post hoc t test, P < .001 and P = .003 at S1 and L4, respectively). The Ahn et al and Fattori et al classifications were of limited value. CONCLUSION: The data suggest that only dural sac ratio at L5 and S1 and a sagittal dural sac width at S1 greater than that at L4 are statistically significant criteria for the assessment of dural ectasia in children, adolescents, and young adults.     

Determination of wall shear stress in the aorta with the use of MR phase velocity mapping

MR phase velocity mapping was used to calculate wall shear stress (WSS) in the suprarenal and infrarenal abdominal aorta, two sites with very different proclivities for development of atherosclerosis. For the eight subjects studied, the average value of the mean (tune averaged over the cardiac cycle) WSS in the suprarenal aorta was 10.4 dynes/cm² at the posterior wall and 8.6 at the anterior wall. In the infrarenal aorta, WSS values were 4.7 at the posterior wall and 6.1 at the anterior wall. Peak WSS over the cardiac cycle was 48 and 54 at the anterior and posterior walls of the suprarenal aorta, respectively, and 33 and 30 at the anterior and posterior walls of the infrarenal aorta, respectively. Wide variation was found in both mean and peak WSS values among subjects. However, for 28 of 32 locations examined, mean and peak WSS were ingher in the suprarenal aorta than in the infrarenal aorta. Because atherosclerosis is more likely to form in the infrarenal aorta than in the suprarenal aorta, tins study supports the hypothesis that low WSS is a localizing factor for atherosclerosis, and ingh WSS may act as a deterrent against formation of atherosclerosis.     

Mitral valve flow measured with cine MR velocity mapping in patients with ischemic heart disease: comparison with doppler echocardiography

Diastolic function is an important element of overall left ventricular function. The pattern of flow across the mitral valve is commonly used as a measure of diastolic ventricular function. Magnetic resonance (MR) velocity mapping of blood flow across the mitral valve was compared with Doppler echocardiography. Nineteen patients with known coronary artery disease (mean age. 62 years: 11 with previous myocardial infarction) were studied. The mean value of peak early filling velocity (± standard deviation) was 60.1 cm/sec ± 14.3 with the MR method and 59.4 cm/sec ± 13.7 with echocardiography (P = 0.732). The mean difference between the two measurements (95% confidence interval) was ?0.8 cm/sec (?5.2 cm/sec. +2.2 cm/sec). The mean value of early deceleration was 4.3 mlsec² ± 1.5 with the MR method and 4.0 m/sec² ± 1.5 with echocardiography (P = 0.073). The mean Werence was ?0.4 cm/sec² (?0.92 cm/eec². +0.05 cm/sec²). The mean value of peak atriosystolic velocity was 51 cm/sec ± 14.6 with the MR method and 62 cm/sec ± 17.2 with echocardiography (P = 0.002). The mean difference was ?11 cm/sec (?18.1 cm/sec, ?3.45 cm /sec). Peak atrial filling was consistently lower with the MR method than with echocardiography. Time-averaged measurements of ventricular fflling with MR velocity mapping are an accurate measure of early diastolic filling but underestimate the velocity of atriosystolic fflling.     

Mitral and aortic valvular flow: quantification with MR phase mapping.

When magnetic resonance phase mapping is used to quantitate valvular blood flow, the presence of higher-order-motion terms may cause a loss of phase information. To overcome this problem, a sequence with reduced encoding for higher-order motion was used, achieved by decreasing the duration of the flow-encoding gradient to 2.2 msec. Tested on a flow phantom simulating a severe valvular stenosis, the sequence was found to be robust for higher-order motion within the clinical velocity range. In eight healthy volunteers, mitral and aortic volume flow rates and peak velocities were quantified by means of phase mapping and compared with results of the indicator-dilution technique and Doppler echocardiography, respectively. Statistically significant correlations were found between phase mapping and the other two techniques. Similar studies in patients with valvular disease indicate that phase mapping is also valid for pathologic conditions. Phase mapping may be used as a noninvasive clinical tool for flow quantification in heart valve disease.     

Selective MR imaging approach for evaluation of patients with Horner's syndrome.

PURPOSE: To assess the usefulness of MR in the evaluation of patients with Horner's syndrome. PATIENTS AND METHODS: We prospectively performed MR imaging in 33 patients with Horner's syndrome (13 preganglionic and 20 postganglionic) using a protocol specifically designed for pre- and postganglionic varieties of this syndrome. Assignment of patients to pre- or postganglionic categories was performed on the basis of pharmacologic testing. RESULTS: Abnormalities in one-half of the patients with preganglionic Horner's syndrome included lateral medullary infarct, spinal cord/root disease, apical lung tumor, and paravertebral metastatic mass. Three of 20 patients with postganglionic Horner's syndrome had carotid artery dissection. CONCLUSION: Routine scanning of patients who have postganglionic Horner's syndrome with cluster headaches was not helpful in our small series.     

Spinal imaging features in Japanese patients with Marfan syndrome: a case-control study

Purpose

The purpose of our study was to evaluate the morphology of the lumbosacral spine, i.e. the dura and vertebral body shape, of Japanese patients with Marfan syndrome (MFS) by comparing it with sex- and age-matched controls.

Materials and methods

Spinal MR or CT images of 32 MFS patients and 32 controls were retrospectively reviewed. The anteroposterior dural sac diameter (DSD), anteroposterior vertebral body diameter (VBD), and vertebral body height (VBH) were measured from L1 to S1 levels and the dural sac ratio [DSR = (DSD/VBD)] and vertebral body aspect ratio [VAR = (VBH/VBD)] were calculated.

Results

At each level, mean DSD and DSR were significantly higher in MFS patients; VBD was not. The cutoff values for DSR to differentiate between MFS patients and the controls were 0.59, 0.46, 0.42, 0.45, 0.47, and 0.47 from the level of L1 to S1. At a sensitivity of 93.8 % and a specificity of 84.4 % the cutoff value at S1 was most diagnostic. In MFS patients VAR was significantly higher at L3 and L4.

Conclusion

Our cutoff value for DSR >0.47 at S1 may help to identify MFS in the Japanese population. A square-like appearance of the L3 and L4 vertebral bodies is a supplementary finding in MFS patients.     

Encephalopathy in AIDS patients: evaluation with MR imaging

The presence and extent of encephalopathy were evaluated in 47 patients with AIDS or AIDS-related complex (ARC) by the use of MR imaging. Twenty-nine (62%) of the patients showed some form of white matter disease, exhibited as high signal intensity on T2-weighted images. Focal white matter lesions were seen in 23 (49%) of the patients, while a diffuse white matter process was observed in six patients (13%). Of the 29 patients who had white matter disease on MR scans, 17 (36%) had a suggestion of white matter involvement on an initial CT study. Meanwhile, 12 (26%) of the patients had a normal CT scan on the initial examination. MR findings showed predominant disease in the subinsular and peritrigonal white matter areas. Marked cerebral atrophy was observed in 17 (36%) of 47 patients, cerebellar atrophy in 18 (38%), and brainstem atrophy in seven patients (15%). Pathologic findings showed that toxoplasmosis was present in eight patients (17%), and primary CNS lymphoma was present in three patients (6%). Cryptococcal meningitis was noted in two (4%) of the patients at autopsy, and Mycobacterium tuberculosis was seen in one (2%) of the patients at autopsy. MR imaging has been shown to be a valuable technique for the detection of encephalopathy in AIDS patients.     

MR flow mapping in coronary artery bypass grafts: a validation study with Doppler flow measurements.

PURPOSE: To validate fast magnetic resonance (MR) flow mapping with intravascular Doppler flow measurements in vitro and in patients with nonstenotic and stenotic coronary artery bypass grafts. MATERIALS AND METHODS: MR and Doppler flow measurements were performed in a small-diameter flow phantom with physiologic flow conditions and at baseline and during adenosine stress in 27 grafts in 23 patients, who were scheduled for cardiac catheterization. At invasive analysis, the grafts were divided into those with stenosis of less than 50% (nonstenotic) and those with stenosis greater than or equal to 50% (stenotic). In vitro velocity values and velocity values in nonstenotic and stenotic grafts were compared with linear regression analysis, and the in vitro interstudy variability was determined. RESULTS: Excellent correlations in average peak velocity (r = 0.99, P <.001) and diastolic peak velocity (r = 0.99, P <.001) were demonstrated in vitro between MR and Doppler flow measurements, with less than 5% interstudy variability. MR and Doppler flow measurements revealed good correlations in peak velocity and velocity reserve both in nonstenotic (n = 20) (average peak velocity: r = 0.81, P <.001; diastolic peak velocity: r = 0.83, P <.001; velocity reserve: r = 0.56, P =.010) and stenotic (n = 7) (average peak velocity: r = 0.83, P <.001; diastolic peak velocity: r = 0.78, P =.001; velocity reserve: r = 0.70, P =.078) grafts. CONCLUSION: Fast MR flow mapping provides noninvasive measures of peak velocity and velocity reserve, which closely correlate with Doppler values both in vitro and in nonstenotic and stenotic grafts.