Victoria Parish

Cardiovascular magnetic resonance myocardial feature tracking detects quantitative wall motion during dobutamine stress

BackgroundDobutamine stress cardiovascular magnetic resonance (DS-CMR) is an established tool to assess hibernating myocardium and ischemia. Analysis is typically based on visual assessment with considerable operator dependency. CMR myocardial feature tracking (CMR-FT) is a recently introduced technique for tissue voxel motion tracking on standard steady-state free precession (SSFP) images to derive circumferential and radial myocardial mechanics.We sought to determine the feasibility and reproducibility of CMR-FT for quantitative wall motion assessment during intermediate dose DS-CMR.Methods10 healthy subjects were studied at 1.5 Tesla. Myocardial strain parameters were derived from SSFP cine images using dedicated CMR-FT software (Diogenes MRI prototype; Tomtec; Germany). Right ventricular (RV) and left ventricular (LV) longitudinal strain (EllRV and EllLV) and LV long-axis radial strain (ErrLAX) were derived from a 4-chamber view at rest. LV short-axis circumferential strain (EccSAX) and ErrSAX; LV ejection fraction (EF) and volumes were analyzed at rest and during dobutamine stress (10 and 20 μg · kg-1· min-1).ResultsIn all volunteers strain parameters could be derived from the SSFP images at rest and stress. EccSAX values showed significantly increased contraction with DSMR (rest: -24.1 ± 6.7; 10 μg: -32.7 ± 11.4; 20 μg: -39.2 ± 15.2; p < 0.05). ErrSAX increased significantly with dobutamine (rest: 19.6 ± 14.6; 10 μg: 31.8 ± 20.9; 20 μg: 42.4 ± 25.5; p < 0.05). In parallel with these changes; EF increased significantly with dobutamine (rest: 56.9 ± 4.4%; 10 μg: 70.7 ± 8.1; 20 μg: 76.8 ± 4.6; p < 0.05). Observer variability was best for LV circumferential strain (EccSAX ) and worst for RV longitudinal strain (EllRV) as determined by 95% confidence intervals of the difference.ConclusionsCMR-FT reliably detects quantitative wall motion and strain derived from SSFP cine imaging that corresponds to inotropic stimulation. The current implementation may need improvement to reduce observer-induced variance. Within a given CMR lab; this novel technique holds promise of easy and fast quantification of wall mechanics and strain.

Congenital Heart Disease: Cardiovascular MR Imaging by Using an Intravascular Blood Pool Contrast Agent

PURPOSEnTo compare the image quality and diagnostic performance of a contrast agent-specific inversion-recovery (IR) steady-state free precession (SSFP) magnetic resonance (MR) imaging sequence performed by using an intravascular contrast agent (gadofosveset trisodium) with those of a commonly used T2-prepared SSFP sequence performed by using an extravascular (gadopentetate dimeglumine) and an intravascular (gadofosveset trisodium) contrast agent in patients with congenital heart disease (CHD).nnnMATERIALS AND METHODSnThe local ethics committee and the United Kingdom Medicines and Healthcare products Regulatory Agency approved this study. Patient informed consent was obtained. Twenty-three patients with CHD were examined by using a 1.5-T MR imaging unit and a 32-channel coil. Gadopentetate dimeglumine and gadofosveset trisodium were used in the same patient on consecutive days. Vessel wall sharpness, contrast-to-noise ratios (CNRs), image quality, and diagnostic performance achieved by using the IR SSFP sequence with gadofosveset trisodium were compared with those achieved by using the T2-prepared SSFP sequence with gadopentetate dimeglumine and gadofosveset trisodium and with those achieved at respective contrast material-enhanced MR angiographic examinations. The Wilcoxon rank sum test was used to compare categoric variables; t tests were used to compare continuous variables.nnnRESULTSnUse of the IR SSFP sequence with gadofosveset trisodium significantly improved vessel wall sharpness, CNRs, and image quality (P < .05 for all) for all investigated intra- and extracardiac structures compared with the T2-prepared SSFP sequence with gadopentetate dimeglumine and gadofosveset trisodium and the respective contrast-enhanced MR angiographic examinations. With use of the IR SSFP sequence with gadofosveset trisodium, new, unsuspected diseases (five [22%] of 23) were diagnosed, while other diseases could be excluded (15 [65%] of 23). Information available from echocardiography (n = 23), conventional angiography (n = 4), and/or surgery (n = 1) confirmed all diagnoses.nnnCONCLUSIONnIR SSFP with gadofosveset trisodium improved image quality and diagnostic performance, allowing a more accurate and complete assessment of cardiovascular anatomy in patients with CHD compared with T2-prepared SSFP with gadopentetate dimeglumine and gadofosveset trisodium and respective contrast-enhanced MR angiographic examinations.

Dobutamine stress MRI in repaired tetralogy of Fallot with chronic pulmonary regurgitation: A comparison with healthy volunteers

BACKGROUNDnTo compare the ventricular response to dobutamine stress between adult patients with chronic pulmonary regurgitation (PR) after repair of tetralogy of Fallot (r-TOF) and healthy volunteers using a staged dobutamine stress MR (DS-MR) protocol.nnnMETHODSnEighteen r-TOF patients (median age 31.9 years, range 16.2-60.1) with severe PR and 10 healthy controls (median age 40.6 years, range 23.9-51.8) completed staged DS-MR (baseline, 10 and 20 μg/kg/min) with ventricular volumetry and pulmonary flow quantification. Comparative analysis involved 3-way ANOVA, t-test, regression analysis, and coefficient of variance.nnnRESULTSnAll controls had significant increase of ejection fraction (EF) at each stress level for both ventricles (normal contractile reserve, all p<0.05). In r-TOF patients (RV-EDV 126 ± 27 ml/m(2), RV-EF 55 ± 7%, LV-EF 58 ± 6%, PR-fraction 43 ± 15%), low-dose DS-MR at 10 μg/kg/min demonstrated normal biventricular contractile reserve as seen in volunteers. On increase from 10 to 20 μg/kg/min a subgroup showed worsening ejection fraction (n=8, p<0.05), mainly due to lack of reduction or even increase of RV-ESV, while the remainder responded with further reduction of RV-ESV and RV-EDV (n=10, p<0.05) and a non-significant trend to increased EF. This different response could not be predicted at baseline.nnnCONCLUSIONSnIn r-TOF patients with chronic PR, DS-MR at 10 μg/kg/min showed normal biventricular systolic response compared with controls. Increase to 20 μg/kg/min provoked abnormal RV-ESV response in some r-TOF patients, suggesting presence of ventricular systolic dysfunction not evident at rest.

Single breath-hold assessment of cardiac function using an accelerated 3D single breath-hold acquisition technique - comparison of an intravascular and extravascular contrast agent

BackgroundCardiovascular magnetic resonance (CMR) is the current gold standard for the assessment of left ventricular (LV) function. Repeated breath-holds are needed for standard multi-slice 2D cine steady-state free precession sequences (M2D-SSFP). Accelerated single breath-hold techniques suffer from low contrast between blood pool and myocardium. In this study an intravascular contrast agent was prospectively compared to an extravascular contrast agent for the assessment of LV function using a single-breath-hold 3D-whole-heart cine SSFP sequence (3D-SSFP).MethodsLV function was assessed in fourteen patients on a 1.5u2009T MR-scanner (Philips Healthcare) using 32-channel coil technology. Patients were investigated twice using a 3D-SSFP sequence (acquisition time 18–25u2009s) after Gadopentetate dimeglumine (GdD, day 1) and Gadofosveset trisodium (GdT, day 2) administration. Image acquisition was accelerated using sensitivity encoding in both phase encoding directions (4xSENSE). CNR and BMC were both measured between blood and myocardium. The CNR incorporated noise measurements, while the BMC represented the coeffiancy between the signal from blood and myocardium [1]. Contrast to noise ratio (CNR), blood to myocardium contrast (BMC), image quality, LV functional parameters and intra-/interobserver variability were compared. A M2D-SSFP sequence was used as a reference standard on both days.ResultsAll 3D-SSFP sequences were successfully acquired within one breath-hold after GdD and GdT administration. CNR and BMC were significantly (pu2009<u20090.05) higher using GdT compared to GdD, resulting in an improved endocardial definition. Using 3D-SSFP with GdT, Bland–Altman plots showed a smaller bias (95% confidence interval LVEF: 9.0 vs. 23.7) and regression analysis showed a stronger correlation to the reference standard (R2u2009=u20090.92 vs. R2u2009=u20090.71), compared to 3D-SSFP with GdD.ConclusionsA single-breath-hold 3D-whole-heart cine SSFP sequence in combination with 32-channel technology and an intravascular contrast agent allows for the accurate and fast assessment of LV function.Trial registrationThe study was approved by the local research ethics committee (Study No. 07/Q0704/2) and was registered with the Medicines and Healthcare Products Regulatory Agency (MHRA Study No. 28482/0002/001–0001, EudraCTnumber 2006–007042).

Planning of catheter interventions for pulmonary artery stenosis: improved measurement agreement with magnetic resonance angiography using identical angulations.

Objectives: To evaluate the current disagreement between the gold standard X‐ray angiography (XRA) and magnetic resonance angiography (MRA) for the measurement of peripheral pulmonary artery stenosis (PPAS). Background: MRA may help planning of catheter interventions for PPAS. However, there are sources of disagreement between XRA and MRA as measures are performed differently. We hypothesized that agreement may improve if identical angulation views are used. Methods: In this retrospective study, 17 patients were included. Four independent observers analyzed the pictures in three technique modalities: (1) XRA, (2) cross‐sectional‐MRA: reformatted to obtain the perpendicular cut‐off view of the vessel, and (3) angulated‐MRA: reformatted using the same angulations used in XRA. We measured: (a) minimal diameter at stenosis, (b) vessel diameter 1 cm proximal, and (c) 1 cm distal to the stenosis. Results: While in elliptical vessels cross‐sectional‐MRA provided both the larger and smaller diameter, XRA and angulated‐MRA typically provided only the larger diameter due to projections. We found poor agreement between the smaller diameter in cross‐sectional‐MRA and XRA. XRA underestimate the diameter at the three locations (<15–22%). However, there was a good agreement between the larger cross‐sectional‐MRA diameter and XRA. This further improved if MRA images were reformatted with the identical angulations used in XRA (angulated‐MRA). Conclusions: Conventional cross‐sectional‐MRA measurements of PPAS only moderately agree with XRA. However, using identical angulations in MRA reduces the bias. Hence, MRA is a valuable tool for planning angulations and measurements of PPAS prior to catheter interventions.

Novel System for Real-Time Integration of 3-D Echocardiography and Fluoroscopy for Image-Guided Cardiac Interventions: Preclinical Validation and Clinical Feasibility Evaluation

Real-time imaging is required to guide minimally invasive catheter-based cardiac interventions. While transesophageal echocardiography allows for high-quality visualization of cardiac anatomy, X-ray fluoroscopy provides excellent visualization of devices. We have developed a novel image fusion system that allows real-time integration of 3-D echocardiography and the X-ray fluoroscopy. The system was validated in the following two stages: 1) preclinical to determine function and validate accuracy; and 2) in the clinical setting to assess clinical workflow feasibility and determine overall system accuracy. In the preclinical phase, the system was assessed using both phantom and porcine experimental studies. Median 2-D projection errors of 4.5 and 3.3 mm were found for the phantom and porcine studies, respectively. The clinical phase focused on extending the use of the system to interventions in patients undergoing either atrial fibrillation catheter ablation (CA) or transcatheter aortic valve implantation (TAVI). Eleven patients were studied with nine in the CA group and two in the TAVI group. Successful real-time view synchronization was achieved in all cases with a calculated median distance error of 2.2 mm in the CA group and 3.4 mm in the TAVI group. A standard clinical workflow was established using the image fusion system. These pilot data confirm the technical feasibility of accurate real-time echo-fluoroscopic image overlay in clinical practice, which may be a useful adjunct for real-time guidance during interventional cardiac procedures.

Extended-field-of-view three-dimensional transesophageal echocardiography using image-based X-ray probe tracking

The use of ultrasound imaging for guidance of cardiac interventional procedures is limited by the small field of view of the ultrasound volume. A larger view can be created by image-based registration of several partially overlapping volumes, but automatic registration is likely to fail unless the registration is initialized close to the volumes correct alignment. In this article, we use X-ray images to track a transesophageal ultrasound probe and thereby provide initial position information for the registration of the ultrasound volumes. The tracking is possible using multiple X-rays or just a single X-ray for each probe position. We test the method in a phantom experiment and find that with at least 50% overlap, 88% of volume pairs are correctly registered when tracked using three X-rays and 86% when using single X-rays. Excluding failed registrations with errors greater than 10 mm, the average registration accuracy is 2.92 mm between ultrasound volumes and 4.75 mm for locating an ultrasound volume in X-ray space. We conclude that the accuracy and robustness of the registrations are sufficient to provide useful images for interventional guidance.

Three-modality registration for guidance of minimally invasive cardiac interventions

Image guidance of minimally invasive cardiac interventions can be augmented by registering together different imaging modalities. In this paper, we propose a method to combine three modalities: X-ray fluoroscopy, trans-esophageal ultrasound and pre-procedure MRI or CT. The registration of the pre-procedure image involves a potentially unreliable manual initialisation of its position in an X-ray projection view. The method therefore includes an automatic correction using the esophagus location as an additional constraint. We test the method in a phantom experiment and find that initialising the pre-procedure image with up to 9mm offset from its correct position results in a 92% registration success rate. The esophagus constraint improves the capture range in the out-of-plane direction, which simplifies the manual initialisation.

Higher dose dobutamine stress MR imaging in repaired Tetralogy of Fallot: observer variance of volumetric assessment compared with normal volunteers.

To investigate changes in image quality and observer variance between rest and higher‐dose dobutamine stress MR imaging (DS‐MR) in tetralogy of Fallot (TOF) patients and in a group of normal healthy volunteers using both axial and short axis orientation for cardiac volumetric assessment.

Cardiac magnetic resonance myocardial feature tracking correlates with natural radial strain and corresponds to inotropic stimulation

Summary We have demonstrated that cardiac magnetic resonance (CMR) myocardial feature tracking (FT) and natural radial strain correlate and correspond to inotropic stimulation. CMR-FT has the potential for quantitative wall motion assessment at rest and during dobutamine stress magnetic resonance (DSMR) imaging. Background CMR-FT is a recently introduced technique for tissue voxel motion tracking on standard steady-state free precession (SSFP) images to derive radial myocardial mechanics. CMR-FT has the potential to facilitate DSMR analysis however has not yet been compared to external reference standards (with stress) such as SSFP derived natural radial strain. Methods 10 healthy subjects were studied at 1.5 Tesla. LV shortaxis radial strain ErrSAX was derived from SSFP cine images using dedicated CMR-FT software (Diogenes MRI prototype, Tomtec, Germany) at rest and during dobutamine stress (10 and 20 μg * kg-1* min-1). Natural radial strain values (loge [End-systolic wall thickness/ end-diastolic wall thickness]) were calculated in identical segments as analysed for ErrSAX using commercially available software (Philips View Forum, The Netherlands). 95% confidence intervals (CI) of the difference and p-values were calculated to compare the 2 techniques. Results In all volunteers strain parameters could be derived from the SSFP images at rest and stress. ErrSAX values showed significantly increased contraction with DSMR (rest: 19.6±14.6; 10 μg: 31.8±20.9; 20 μg: 42.4±25.5, p<0.05). Natural radial strain values increased with dobutamine (rest: 24±8.9; 10 μg: 36.5±8.9; 20 μg: 44.2 ±8.5, p<0.05). There was reasonable agreement between mean ErrSAX and natural radial strain at rest and with dobutamine stress (figure 1 and table 1) as determined by 95% CI of the difference. Conclusions