2D Cine MRI Research Articles

From unicuspid to quadricuspid: the impact of aortic valve morphology on 3D hemodynamics

Background The purpose of this study was to assess the impact of aortic valve morphology on aortic 3D blood flow dynamics and wall shear stress (WSS) in normal and a wide range of congenitally altered aortic valves ranging from unicuspid to quadricuspid morphology. Methods In-vivo aortic 3D hemodynamics were evaluated by MRI in 17 patients with unicuspid (n=3), bicuspid (n=9, 3 true bicuspid, 3 right-left (RL) coronary leaflet fusion, and 3 right-non (RN) coronary leaflet fusion), trileaflet (n=3), and quadricuspid aortic valves (n=2). Valve morphology and dynamics were assessed using 2D CINE MRI. Aortic blood flow was measured using ECG and respiration synchronized 4D flow MRI with full volumetric coverage of the aorta. Data analysis included co-registered visualization of aortic valve morphology with systolic 3D blood flow and grading of valve-specific aortic out-flow patterns. The influence of valve geometry on aortic hemodynamics was quantified by calculation of valve flow angle and segmental distribution of ascending aorta WSS. Results All congenitally altered valves showed marked flow derangement, elevated velocity jets along the aortic wall and distinct flow impingement locations. While all RLBAV valves were associated with flow jets directed towards the right anterior aortic wall, RN-fusion and unicuspid valves showed jet patterns towards the right-posterior wall. Quantitative analysis revealed higher flow angles for unicuspid, true BAV, RN-BAV, RL-BAV, and quadricuspid

대동맥판 역류질환 진단시 이면성심초음파 박출계수의 보정을 통한 오진율 개선에 관한 연구

본 연구는 좌심실의 박출계수가 주된 예후인자인 대동맥판 역류환자를 대상으로 cine MRI와 이면성심초음파의 물리적인 시간해상도 차이를 분석하여 이면성심초음파의 박출계수에 보정함으로써 오진율을 감소시키고자 하였다. 연구대상은 2010년 2월부터 2011년 12월까지 이면성심초음파와 cine MRI를 병행한 환자 110명 중 대동맥판 역류환자 37명을 대상으로 하였다. 각 검사 장비별로 이완기말 면적, 수축기말 면적, 일회 심박출 면적을 측정하였으며, 측정된 값을 이용하여 박출계수를 구하고, 이면성심초음파와 cine MRI의 정상 수치 범위를 비교하여 보정 전 오진율을 평가하였다. 이면성심초음파와 cine MRI의 물리적인 시간해상도 차이는 두 측정치간의 상관관계를 알아본 후 선형회귀분석을 이용하여 회귀계수를 도출하고 도출된 회귀계수를 이용하여 이면성심초음파의 박출 계수에 보정하였다. 보정된 이면성심초음파 박출계수의 신뢰도를 평가하기 위해 Bland-Altman plot를 통해 측정치간 오차를 분석하였고, 이 수치를 cine MRI의 정상 수치 범위와 비교하여 보정 후 오진율을 재평가하였다. 연구결과, 이면성심초음파 박출계수의 물리적 시간해상도 보정 전 오진율은 32.4%(12명)로 높게 나왔고, 보정 후 오진율은 18.9%(7명)로 13.5% 감소하였다. 또한 Bland-Altman plot에서 확인한 보정된 이면성심초음파 박출계수는 cine MRI의 박출계수와의 일치도가 상당히 높다는 것을 알 수 있다. 결론적으로 대동맥판 역류질환 진단시 단순한 이면성심초음파의 박출계수로만 감별하는 것은 오진율을 높일 수 있으므로 오진율이 낮은 cine MRI장비의 물리적 특성을 고려한 시간해상도의 차이를 보정함이 중요하며, 본 연구를 통하여 오진율 감소를 확인할 수 있었으므로 임상 적용의 유용성이 높다고 사료된다. This study is aimed at decreasing wrong diagnosis with corrected EF(Ejection Fraction) of 2D echo cardiography by analysing the physical time-resolution difference between Cine MRI and 2D echo cardiography and applying the corrected EF in 2D echocardiography. From February 2010 to December 2011, among the 110 patients who had undergone both 2D echo cardiography and cine MRI only 37 patient were selected suffering aortic valve regurgitation. ED, ES and SV were measured and EF was calculated in each system while normal ranges of Cine MRI and 2D echocardiography were compared to evauate misdiagnosis rate. The correlation of physical time resolution between 2D echocardiography and MRI was evaluated and the differences were corrected with linear regression coefficient which is derived from linear regression analysis. Blandt-Altman plot was used to evaluate the reliability of corrected 2D echo cardiography EF and compare the error among measured values. The values were compared with MRI normal range and misdiagnosis rate was measured again. As a result, misdiagnosis rates of physical time resolution were measured to be 32.4%(12people) before the correction of EF and 18.9%(7people) after the correction. Also, EF confirmed in Blandt-Altman plot were almost the same with MRI EF. In conclusion, when diagnosing aortic regurgitation disease, simply using 2D echocardiography can easily raise the misdiagnosis rates, therefore considering the MRI machine's physical merits, correcting the time resolution difference is important by calculating time resolution wrong diagnosis would decrease and it is considered to be useful in clinical circumstances.

Group sparse reconstruction using intensity-based clustering

Compressed sensing has been of great interest to speed up the acquisition of MR images. The k-t group sparse (k-t GS) method has recently been introduced for dynamic MR images to exploit not just the sparsity, as in compressed sensing, but also the spatial group structure in the sparse representation. k-t GS achieves higher acceleration factors compared to the conventional compressed sensing method. However, it assumes a spatial structure in the sparse representation and it requires a time consuming hard-thresholding reconstruction scheme. In this work, we propose to modify k-t GS by incorporating prior information about the sorted intensity of the signal in the sparse representation, for a more general and robust group assignment. This approach is referred to as group sparse reconstruction using intensity-based clustering. The feasibility of the proposed method is demonstrated for static 3D hyperpolarized lung images and applications with both dynamic and intensity changes, such as 2D cine and perfusion cardiac MRI, with retrospective undersampling. For all reported acceleration factors the proposed method outperforms the original compressed sensing method. Improved reconstruction over k-t GS method is demonstrated when k-t GS assumptions are not satisfied. The proposed method was also applied to cardiac cine images with a prospective sevenfold acceleration, outperforming the standard compressed sensing reconstruction.

Single breathhold three-dimensional cardiac cine MRI with whole ventricular coverage and retrospective cardiac gating using kat ARC

Summary This work presents a kt acceleration method (kat ARC) for retrospective cardiac-gated 3D cardiac cine MRI. Our in-vivo results show that 3D cine images of the entire ventricle are obtainable within a single breathhold using highly accelerated kat ARC. Background For quantitative volumetric assessments of cardiac function, 3D cine images depicting motion of the entire ventricle in a complete cardiac cycle are needed. However, due to limited acceleration capability, breathheld 3D cine MRI is not obtainable using conventional parallel imaging. Several kt-acceleration methods have demonstrated high-acceleration capability for dynamic MRI by exploiting spatiotemporal correlation [Tsao, MRM 2003; Huang, MRM 2005]. This study aims to investigate the feasibility of breathheld retrospective cardiac-gated whole-ventricle 3D cine MRI using kat ARC (k-adaptive-t Autocalibrating Reconstruction for Cartesian sampling [Lai, ISMRM 2009]). Methods

Four‐dimensional magnetic resonance imaging (4D‐MRI) using image‐based respiratory surrogate: A feasibility study

Four-dimensional computed tomography (4D-CT) has been widely used in radiation therapy to assess patient-specific breathing motion for determining individual safety margins. However, it has two major drawbacks: low soft-tissue contrast and an excessive imaging dose to the patient. This research aimed to develop a clinically feasible four-dimensional magnetic resonance imaging (4D-MRI) technique to overcome these limitations. The proposed 4D-MRI technique was achieved by continuously acquiring axial images throughout the breathing cycle using fast 2D cine-MR imaging, and then retrospectively sorting the images by respiratory phase. The key component of the technique was the use of body area (BA) of the axial MR images as an internal respiratory surrogate to extract the breathing signal. The validation of the BA surrogate was performed using 4D-CT images of 12 cancer patients by comparing the respiratory phases determined using the BA method to those determined clinically using the Real-time position management (RPM) system. The feasibility of the 4D-MRI technique was tested on a dynamic motion phantom, the 4D extended Cardiac Torso (XCAT) digital phantom, and two healthy human subjects. Respiratory phases determined from the BA matched closely to those determined from the RPM: mean (± SD) difference in phase: -3.9% (± 6.4%); mean (± SD) absolute difference in phase: 10.40% (± 3.3%); mean (± SD) correlation coefficient: 0.93 (± 0.04). In the motion phantom study, 4D-MRI clearly showed the sinusoidal motion of the phantom; image artifacts observed were minimal to none. Motion trajectories measured from 4D-MRI and 2D cine-MRI (used as a reference) matched excellently: the mean (± SD) absolute difference in motion amplitude: -0.3 (± 0.5) mm. In the 4D-XCAT phantom study, the simulated "4D-MRI" images showed good consistency with the original 4D-XCAT phantom images. The motion trajectory of the hypothesized "tumor" matched excellently between the two, with a mean (± SD) absolute difference in motion amplitude of 0.5 (± 0.4) mm. 4D-MRI was able to reveal the respiratory motion of internal organs in both human subjects; superior-inferior (SI) maximum motion of the left kidney of Subject #1 and the diaphragm of Subject #2 measured from 4D-MRI was 0.88 and 1.32 cm, respectively. Preliminary results of our study demonstrated the feasibility of a novel retrospective 4D-MRI technique that uses body area as a respiratory surrogate.

Measurement of temporal changes in vocal tract area function from 3D cine-MRI data

A 3D cine-MRI technique was developed based on a synchronized sampling method [Masaki et al., J. Acoust. Soc. Jpn. E 20, 375-379 (1999)] to measure the temporal changes in the vocal tract area function during a short utterance /aiueo/ in Japanese. A time series of head-neck volumes was obtained after 640 repetitions of the utterance produced by a male speaker, from which area functions were extracted frame-by-frame. A region-based analysis showed that the volumes of the front and back cavities tend to change reciprocally and that the areas near the larynx and posterior edge of the hard palate were almost constant throughout the utterance. The lower four formants were calculated from all the area functions and compared with those of natural speech sounds. The mean absolute percent error between calculated and measured formants among all the frames was 4.5%. The comparison of vocal tract shapes for the five vowels with those from the static MRI method suggested a problem of MRI observation of the vocal tract: data from static MRI tend to result in a deviation from natural vocal tract geometry because of the gravity effect.

Pulmonary Vein Imaging: Comparison of 3D Magnetic Resonance Angiography with 2D Cine MRI for Characterizing Anatomy and Size

Pulmonary vein imaging is integral for planning atrial fibrillation ablation procedures. We tested the feasibility of quantifying pulmonary vein ostial diameter using two-dimensional cine cardiac magnetic resonance (2D cine CMR) and three-dimensional magnetic resonance angiography (3D MRA). Nine patients with a history of atrial fibrillation and 20 normal volunteers underwent 2D cine CMR and contrast-enhanced 3D MRA of pulmonary veins on a 1.5 T scanner. Pulmonary vein ostial diameters were measured and pulmonary vein vessel border sharpness was graded qualitatively. Both techniques provided excellent pulmonary vein imaging; however, 3D MRA was faster to perform. The average difference between the systolic and diastolic pulmonary vein diameter was 2.5 mm (23.2%, p < 0.0001) in normal volunteers and 2.2 mm (16.9%, p < 0.0001) in atrial fibrillation patients. The ostial diameter measurements by 3D MRA were significantly larger than on 2D cine CMR. Additionally, the pulmonary vein borders appeared sharper with 2D cine CMR compared to 3D MRA. In conclusion, the 2D images can resolve differences in diameter across the cardiac cycle, while the 3D images provide high quality anatomical depiction but blur borders due to pulsatile motion. We suggest a protocol combining 2D cine CMR and 3D MRA for comprehensive evaluation of pulmonary veins.