A computed method for noninvasive MRI assessment of pulmonary arterial hypertension.
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Humans↗
Biomedical subjects
J Tim Marcus
Publications and source records attributed to J Tim Marcus.
Effects of epoprostenol on right ventricular hypertrophy and dilatation in pulmonary hypertension.
OBJECTIVES: To gain more knowledge of changes in main pulmonary artery flow and right ventricular mass and volumes in patients with pulmonary hypertension during epoprostenol therapy. METHODS: Eleven patients (9 women) were evaluated before the start of therapy and every 4 months thereafter. Right and left ventricular volumes and masses were measured by cine MRI. Flow was measured with MRI velocity quantification. At the same times, 6-min walking tests were performed. Right-heart catheterizations were performed at baseline and after 1 year. RESULTS: Right ventricular mass in the patient group was significantly higher from that in a control group of healthy volunteers (95 +/- 26 g vs 42 +/- 10 g, p < 0.05 [mean +/- SD]), whereas the stroke volume was lower (34 +/- 11 mL vs 81 +/- 11 mL, p < 0.05). The greatest improvement in right ventricular stroke volume (to 41 +/- 11 mL, p < 0.05) took place in the first 4 months. During the 1-year follow-up, right ventricular end-diastolic volume and mass did not change, and mean pulmonary artery pressure remained nearly stable at 55 mm Hg at baseline and 53 mm Hg after 1 year. Pulmonary vascular resistance decreased by 12.5% (p = 0.06). CONCLUSIONS: From these data we conclude that epoprostenol lowers pulmonary vascular resistance, leading to an increase in pulmonary artery flow. This increase in pulmonary artery flow corresponds well with the increase in 6-min walking distance and can be noninvasively monitored by MRI (flow quantification). Right ventricular dilatation and hypertrophy are not reversed by epoprostenol therapy, but do not progress either.
Adult↗
Steady-state free precession with myocardial tagging: CSPAMM in a single breathhold.
A method is presented that combines steady-state free precession (SSFP) cine imaging with myocardial tagging. Before the tagging preparation at each ECG-R wave, the steady-state magnetization is stored as longitudinal magnetization by an alpha/2 flip-back pulse. Imaging is continued immediately after tagging preparation, using linearly increasing startup angles (LISA) with a rampup over 10 pulses. Interleaved segmented k-space ordering is used to prevent artifacts from the increasing signal during the LISA rampup. First, this LISA-SSFP method was evaluated regarding ghost artifacts from the steady-state interruption by comparing LISA with an alpha/2 startup method. Next, LISA-SSFP was compared with spoiled gradient echo (SGRE) imaging, regarding tag contrast-to-noise ratio and tag persistence. The measurements were performed in phantoms and in six subjects applying breathhold cine imaging with tagging (temporal resolution 51 ms). The results show that ghost artifacts are negligible for the LISA method. Compared to the SGRE reference, LISA-SSFP was two times faster, with a slightly better tag contrast-to-noise. Additionally, the tags persisted 126 ms longer with LISA-SSFP than with SGRE imaging. The high efficiency of LISA-SSFP enables the acquisition of complementary tagged (CSPAMM) images in a single breathhold.
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Cine MRI assessment of aortic aneurysm dynamics before and after endovascular repair.
PURPOSE: To evaluate stent-graft and aneurysm wall motions during the cardiac cycle using cine magnetic resonance imaging (MRI) to identify mechanisms of long-term failure of endovascular aneurysm repair (EVAR). METHODS: Prior to and after EVAR in 7 patients with abdominal aortic aneurysms (AAA), 12 MRI images per cardiac cycle were acquired in transverse, sagittal, and coronal planes of the aneurysm. Two independent observers blinded to the aim of the study manually traced stent-graft and aneurysm wall contours. Translation was defined as the maximal displacement of the contours in the peak-systolic image compared to the end-diastolic image. Aneurysm wall motions before and after repair were compared. Stent-graft and aneurysm configuration changes during the cardiac cycle were evaluated. The relation between translation and the degree of angulation of the stent-graft was calculated. RESULTS: The anteroposterior translation of the aneurysm decreased from a median 1.05 mm (range <0.5-1.29) before EVAR to within pixel size (<0.5 mm) after EVAR (p=0.04). The cranial-caudal translation of the aneurysm increased from a median 1.01 mm (range <0.5-1.51) before to 1.69 mm (range 1.1-1.99) after EVAR (p=0.02). In 4 stent-grafts, bending during cardiac systole was observed at the site of maximal angulation of the device. In transverse sections, 2-dimensional pulsatile wall motion of the aneurysm was 0.25 cm(2) (range 0.07-0.29) before and 0.17 cm(2) (range 0.07-0.42) after EVAR (p=0.79). No pulsatility of the stent-graft itself was observed. The correlation coefficient between angulation of the stent-graft and the increase in cranial-caudal translation after EVAR was 0.67 (p>0.05). CONCLUSIONS: After EVAR, increased longitudinal translation of both the aneurysm and stent-graft was observed, indicating downward pulling forces at the proximal fixation site. Secondly, increased bending was seen at the site of maximal angulation, which implies a risk of metal fatigue and fabric damage at sites of stent-graft angulation.
Aged↗
Carotid artery dynamics during head movements: a reason for concern with regard to carotid stenting?
PURPOSE: To evaluate carotid artery mobility patterns during head movements following carotid angioplasty/stenting (CAS). METHODS: In 7 patients (all men; mean age 69 years, range 65-76) who had undergone unilateral CAS, 3D time-of-flight magnetic resonance angiography was performed, visualizing both carotid arteries in 5 different head positions (neutral, turned left and right, and bent forward and backward). Maximum intensity projection reconstructions were obtained to measure angulation at the proximal and distal stent junction. Configuration changes of the stented section of the carotid artery and the unstented contralateral artery were judged. Secondly, transverse sections at the level of the carotid bifurcation and at the skull base were used to calculate torsion shear in the common and internal carotid arteries (CCA, ICA) during left and right head position. Results were expressed as median (range). RESULTS: In neutral head position, maximal angulation at the distal stent junction was 34.3 degrees (32.3 degrees-55.6 degrees). With the head bent forward, this angulation changed to 47.6 degrees (42.6 degrees-85.2 degrees, p=0.028) and when bent backward to 26.5 degrees (25.0 degrees-48.7 degrees, p=0.027). In all patients, configuration changes of the stented sections were absent. The contralateral unstented side showed diffuse configuration changes without specific angulation at one location. With the head turned left and right, the CCA on the stented side was subjected to 28.6 degrees (13.6 degrees-53.7 degrees) and 24.9 degrees (2.0 degrees-50.6 degrees) of torsion shear, respectively. Torsion of the ICA was subsequently 18.1 degrees (12.7 degrees-40.5 degrees) and 15.2 degrees (2.9 degrees-69.4 degrees). CONCLUSIONS: Following carotid stenting, sharp ICA angulation that are aggravated by forward bending of the head occur at the distal stent junction. The stented section of the carotid artery shows complete lack of flexibility despite highly flexible features of hte stents ex vivo. Both the CCA and ICA are subjected to considerable torsion shear with the head turned left and right. This shear is not accommodated by the current stent designs.
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Pulmonary vascular responses to hypoxia and hyperoxia in healthy volunteers and COPD patients measured by electrical impedance tomography.
BACKGROUND: Electrical impedance tomography (EIT) is a noninvasive imaging technique using impedance to visualize and measure blood volume changes. STUDY OBJECTIVE: To examine the validity of EIT in the measurement of hypoxic pulmonary vasoconstriction (HPV) and hyperoxic pulmonary vasodilation in healthy volunteers and COPD patients. PARTICIPANTS: Group 1 consisted of seven healthy volunteers (mean age, 46 years; age range, 36 to 53 years). Group 2 comprised six clinically stable COPD patients (mean age, 65 years; age range, 50 to 74 years). INTERVENTIONS: EIT measurements were performed in healthy subjects while they were breathing room air, 14% oxygen (ie, hypoxia), and 100% oxygen (ie, hyperoxia) through a mouthpiece. Maximal impedance change during systole (DeltaZsys) was used as a measure of pulmonary perfusion-related impedance changes. Stroke volume (SV) was measured by means of MRI. In the COPD group, EIT and SV also were determined, but only in room air and under hyperoxic conditions. RESULTS: The data were statistically compared to data for the room air baseline condition. In the volunteers, the mean (+/- SD) DeltaZsys for the group was 352 +/- 53 arbitrary units (AU) while breathing room air, 309 +/- 75 AU in hypoxia (p < 0.05), and 341 +/- 69 AU in hyperoxia (not significant [NS]). The mean MRI-measured SV was 83 +/- 21 mL while breathing room air, 90 +/- 29) mL in hypoxia (NS), and 94 +/- 19 mL in hyperoxia (p < 0.05). In the COPD patients, the mean DeltaZsys for this group was 222 +/- 84 AU while breathing room air and 255 +/- 83 AU in hyperoxia (p < 0.05). In this group, the SV was 59 +/- 16 mL while breathing room air and 61 +/- 13 mL in hyperoxia (NS). Thus, the volunteer EIT response to hypoxia is not caused by decreased SV, because SV did not show a significant decrease. Similarly, in COPD patients the EIT response to hyperoxia is not caused by increased SV, because SV showed only a minor change. CONCLUSION: EIT can detect blood volume changes due to HPV noninvasively in healthy subjects and hyperoxic vasodilation in COPD patients.
Adult↗
Three-dimensional myocardial strains at end-systole and during diastole in the left ventricle of normal humans.
This paper presents the three-dimensional strains in the normal human left ventricle (LV) at end-systole and during diastole. Magnetic resonance tissue tagging was used to measure strain in the left-ventricular heart wall in 10 healthy volunteers aged between 28 and 61 years. The three-dimensional motion was calculated from the displacement of marker points in short- and long-axis cine images, with a time resolution of 30 msec. Homogeneous strain analysis of small tetrahedrons was used to calculate deformation in 18 regions of the LV over a time span of 300 msec starting at end systole. End-systolic radial strain was largest near the heart base, and circumferential and longitudinal strains were largest near the apex. During diastole, the circumferential-longitudinal shear strain (associated with LV torsion) was found to recover earlier than the axial strains. Assessment of three-dimensional diastolic strain is possible with MR tagging. Comparison of patient strain against normal strain may permit early detection of regional diastolic dysfunction.
Adult↗