Myocardial flow reserve (MFR) is not routinely assessed in myocardial perfusion imaging (MPI) studies but has been hypothesized to affect test accuracy when assessing disease severity by coronary vessel lumenography. Magnetic resonance imaging (MRI) is an emerging diagnostic technique that can both perform MPI and assess MFR. We studied women (n = 184) enrolled in the Women's Ischemia Syndrome Evaluation (WISE) study with symptoms suggesting ischemic heart disease. Tests performed were coronary angiography and MPI by both MR and gated radionuclide single photon emission computed tomography (gated-SPECT). The MFR index was calculated using the MR data acquired at baseline and under vasodilation (dipyridamole) conditions. The study was structured with a pilot and an implementation phase. During the pilot phase (n = 46) data were unmasked and an MFR threshold was defined to divide patients into those with an adequate (AMFRI) or inadequate (IMFRI) MFR index. During the implementation phase, the MFR index threshold was prospectively applied to patients (n = 138). In the implementation phase, MPI ischemia detection accuracy compared to severe (> or = 70%) coronary artery diameter narrowing by angiography was higher in the AMFRI vs. the IMFRI group for MRI (86% vs. 70%, p < 0.05) and gated-SPECT (89% vs. 67%, p < 0.01). The IMFRI group (n = 55, 30% of study population) had a higher resting rate-pressure product compared with the AMFRI group (10,599 +/- 2871 vs. 9378 +/- 2447 bpm mm Hg, p < 0.01), consistent with higher resting myocardial flow. When compared with each other, MRI and gated-SPECT MPI showed no difference in accuracy among MFR groups. Myocardial perfusion patterns in the IMFRI group may have resulted in atypical perfusion patterns, which either masked or mimicked epicardial coronary artery disease.

Abstract-Concentric hypertensive left ventricular (LV) hypertrophy is presumed to be a symmetrical process. Using MRI-derived intramyocardial strain, we sought to determine whether segmental deformation was also symmetrical, as suggested by echocardiography. High echocardiographic LV relative wall thickness in hypertensive LV hypertrophy allows preserved endocardial excursion despite depressed LV midwall shortening (MWS). Depressed MWS is an adverse prognostic indicator, but whether this is related to global or regional myocardial depression is unknown. We prospectively compared MWS derived from linear echocardiographic dimensions with MR strain(ʦ) in septal and posterior locations in 27 subjects with ECG LV hypertrophy in the Losartan Intervention for Endpoint Reduction in Hypertension Study. Although MRI-derived mass was higher in patients than in normal control subjects (124.0Ϯ38.6 versus 60.5Ϯ13.2g/m 2 ; PϽ0.001), fractional shortening (30Ϯ5% versus 33Ϯ3%) and end-systolic stress (175Ϯ22 versus 146Ϯ28 g/cm 2 ) did not differ between groups. However, mean MR(ʦ) was decreased in patients versus normal control subjects (13.9Ϯ6.8% versus 22.4Ϯ3.5%), as was echo MWS (13.4Ϯ2.8% versus 18.2Ϯ1.4%; both PϽ0.001). For patients versus normal control subjects, posterior wall(ʦ) was not different (17.8Ϯ7.1% versus 21.6Ϯ4.0%), whereas septal(ʦ) was markedly depressed (10.1Ϯ6.6% versus 23.2Ϯ3.4%; PϽ0.001). Although global MWS by echocardiography or MRI is depressed in hypertensive LV hypertrophy, MRI tissue tagging demonstrates substantial regional intramyocardial strain(ʦ) heterogeneity, with most severely depressed strain patterns in the septum. Although posterior wall 2D principal strain was inversely related to radius of curvature, septal strain was not, suggesting that factors other than afterload are responsible for pronounced myocardial strain heterogeneity in concentric hypertrophy. Key Words: heart function Ⅲ hypertension Ⅲ hypertrophy Ⅲ heart failure Ⅲ radius of curvature Ⅲ strain patterns L eft ventricular hypertrophy (LVH) is a major adaptive response to chronic pressure overload and a powerful independent predictor of adverse cardiovascular events in hypertension. [1][2][3] However, indicators of left ventricular (LV) endocardial shortening, such as fractional shortening and ejection fraction (EF), do not predict cardiovascular events. LV midwall shortening (MWS), an indirect measure of myocardial performance assessed by transthoracic echocardiography, is decreased in a subset of patients with hypertensive LVH. 4 -7 Patients with LVH and decreased MWS are at increased risk for cardiovascular events despite normal endocardial fractional shortening. 2 Functional studies of isolated papillary muscles from experimental models of chronic pressure overload demonstrated depressed contractility despite normal EF. 8 -10 Taken together, these findings suggest that depressed MWS identifies a maladaptive hypertrophic response in the continuum of adaptation to chronic pressure overload and serves as an important clinical...

Velocity-encoded cine (VEC) imaging is potentially an important clinical diagnostic technique for cardiovascular diseases. Advances in gradient technology combined with segmentation approaches have made possible breathhold VEC imaging, allowing data to be obtained free of respiratory artifacts. However, when using conventional segmentation approaches, spatial and temporal resolutions are typically compromised to accommodate short breathhold times. Here we apply a sparse sampling technique, turbo-BRISK (i.e., segmented block regional interpolation scheme for k-space) to VEC imaging, allowing increased spatial and temporal resolution to be obtained in a short breathhold period. BRISK is a sparse sampling technique with interpolation used to generate unsampled data. BRISK was implemented to reduce the scan time by 70% compared with a conventional scan. Further, turbo-BRISK scans, using segmentation factors up to 5, reduce the scan time by up to 94%. Phantom and in vivo results are presented that demonstrate the accuracy of turbo-BRISK VEC imaging. In vitro validation is performed using conventional magnetic resonance VEC. Pulsatile centerline flow velocity measurements obtained with turbo-BRISK acquisitions were correlated with conventional magnetic resonance imaging measurements and achieved r values of 0.99 +/- 0.004 (mean +/- SD) with stroke volumes agreeing to within 4%. A potential limitation of BRISK is reduced accuracy for rapidly varying velocity profiles. We present low- and high-resolution data sets to illustrate the resolution dependence of this phenomenon and demonstrate that at conventional resolutions, turbo-BRISK can accurately represent rapid velocity changes. In vivo results indicate that centerline velocity waveforms in the descending aorta correlate well with conventional measurements with an average r value of 0.98 +/- 0.01.

Purpose: To show that accuracy of jet flow representation by magnetic resonance (MR) phase-contrast (PC) velocityencoded (VE) cine imaging is dominated by error terms resulting from the temporal distribution of data, and to present a generally applicable data interpolation-based approach to correct for this phenomenon. Materials and Methods:Phase-contrast data were acquired in a stenotic orifice flow phantom using a physiologic pulsatile flow waveform. A temporally registered scan, acquired without data segmentation or interleaving was obtained (17 minutes) and taken as the reference (REF). Conventional PC data sets were acquired using segmentation and data interleaving. An enhanced temporal registration (ETR) algorithm was applied to the acquired data to temporally interpolate component sets and output data at matching time points, thereby reducing temporal dispersion. Results:Compared to the REF data, conventionally processed PC data consistently overestimated peak velocities in laminar jet flow regions (127% Ϯ 28%) and exhibited relatively weak correlations (r ϭ 0.67 Ϯ 0.23). The ETRprocessed data better represented peak velocities (101% Ϯ 13%, P Ͻ 0.001) and correlated more closely with the REF data (r ϭ 0.94 Ϯ 0.05, P Ͻ 0.001). Conclusion:The temporal distribution of PC data impacts the accuracy of velocity representation in pulsatile jet flow. A temporal registration postprocessing algorithm can minimize loss of accuracy.

BackgroundIncreased relative wall thickness in hypertensive left ventricular hypertrophy (LVH) has been shown by echocardiography to allow preserved shortening at the endocardium despite depressed LV midwall circumferential shortening (MWCS). Depressed MWCS is an adverse prognostic indicator, but whether this finding reflects reduced global or regional LV myocardial function, as assessed by three-dimensional (3D) myocardial strain, is unknown.Methods and ResultsCardiac Magnetic Resonance (CMR) tissue tagging permits direct evaluation of regional 3D intramyocardial strain, independent of LV geometry. We evaluated 21 hypertensive patients with electrocardiographic LVH in the LIFE study and 8 normal controls using 3D MR tagging and echocardiography. Patients had higher MR LV mass than normals (116 ± 40 versus 63 ± 6 g/m2, P = 0.002). Neither echocardiographic fractional shortening (32 ± 6 versus 33% ± 3%), LVEF (63% versus 64%) or mean end-systolic stress (175 ± 27 versus 146 ± 28 g/cm2) were significantly different, yet global MWCS was decreased by both echocardiography (13.4 ± 2.8 versus 18.2% ± 1.5%, P < 0.001) and MR (16.8 ± 3.6 versus 21.6% ± 3.0%, P < 0.005). 3D MR MWCS was lower at the base versus apex (P = 0.002) in LVH and greater in lateral and anterior regions versus septal and posterior regions (P < 0.001), contributing to the higher mean global MWCS by MR than echo. MR longitudinal strain was severely depressed in LVH patients (11.0 ± 3.3 versus 16.5% ± 2.5%, P < 0.001) and apical twist was increased (17.5 ± 4.3 versus 13.7 ± 3.7, P < 0.05). Importantly, both circumferential and longitudinal shortening correlated with LV relative wall thickness (R > 0.60, P = 0.001 for both).ConclusionsIn patients with hypertensive LVH, despite normal LV function via echocardiography or CMR, CMR intramyocardial tagging show depressed global MWCS while 3D MR strain revealed marked underlying regional heterogeneity of LV dysfunction.

Block regional interpolation scheme for k space (BRISK) is a sparse sampling approach to allow rapid magnetic resonance imaging of dynamic events. Rapid velocity encoded cine (VEC) imaging with Turbo BRISK is potentially an important clinical diagnostic technique for cardiovascular diseases. Previously we applied BRISK and Turbo BRISK to imaging pulsatile flow in a straight tube. To evaluate the capabilities of Turbo BRISK imaging in more complex dynamic flow fields such as might exist in the human vasculature, an in vitro curved tube model, similar in geometry to the aortic arch, was fabricated and imaged under pulsatile flow conditions. Velocity maps were obtained using conventional VEC and Turbo BRISK (turbo factors 1 through 5). Comparison of the flow fields obtained with each higher order turbo factor showed excellent agreement with conventional VEC with minimal loss of information. Similarly, flow maps showed good agreement with the profiles from a laser Doppler velocimetry model. Turbo-5 BRISK, for example, allowed a 94% savings in imaging time, reducing the conventional imaging time from over 8 min to a near breath-hold imaging period of 31 s. Turbo BRISK shows excellent promise toward the development of a clinical tool to evaluate complex dynamic intravascular flow fields.

We developed BRISK-CON-VPS, a rapid phase-contrast cine approach that is a hybrid of the BRISK-VPS (Block Regional Interpolation Scheme for k-space) and conventional (CONV-VPS) scanning employing k-space views per segment (VPS). BRISK-CON-VPS allows data acquisition approximately four times faster than CONV-VPS imaging and has the advantage compared to BRISK-VPS that it can potentially be incorporated into real-time applications. In BRISK-CON-VPS contiguous regions of k-space are sampled using a views per segment factor that is varied as a function of distance from the k-space center. Computational fluid dynamics (CFD) data were used to simulate CONV-VPS, BRISK-VPS, and BRISK-CON-VPS. BRISK-CON-VPS was simulated by incrementing the VPS progressively with increasing distance from the k-space origin while BRISK-VPS was simulated using a uniform VPS applied to the sparse sampling scheme. Simulations showed that up to a base VPS of 5, both BRISK-CON-VPS and BRISK-VPS retained excellent axial-velocity accuracy. Secondary in-plane velocity flow fields were well represented with BRISK-CON-VPS and BRISK-VPS up to a base VPS of 3. CONV-VPS, BRISK-CON-VPS, and BRISK-VPS were applied in vivo and shown to provide comparable quantitative flow data. BRISK-CON-VPS accomplishes breath-hold acquisitions as efficiently as BRISK-VPS, but without requiring data interpolation or under-sampling k-space.

Purpose: To test the potential of a phase contrast magnetic resonance (PC-MR) sparse sampling technique, fragmented regional interpolation segmentation for k-space (FRISK), to capture complex flow features within a breathhold duration by using numerical simulations and experimental approaches. Materials and Methods:Computational fluid dynamics (CFD) data of three models were generated: a two-chamber orifice flow model simulating valvular regurgitation, a femoral artery model, and a U-shaped model simulating the aortic arch. These data were used to simulate conventional and FRISK PC-MR data acquisitions. FRISK parameters can be adapted for different flow fields to capture either high temporal information or complexly varying spatial information with a temporal component or a mixture of both. In vivo PC-MR images on a healthy volunteer were sampled to compare conventional PC-MR with novel FRISK imaging.Results: In our simulations of three representative models, when only the errors from different sampling sequences were considered, FRISK was shown to maintain or even improve data accuracy while cutting the scan time by at least 50% compared to corresponding conventional PC-MR. By adapting the FRISK parameters for flowfields with different features, FRISK was capable of capturing in-plane and through-plane velocity information with excellent detail in approximately 20 heartbeats breathhold duration. The results of the in vivo MR experiment were consistent with the simulation results, showing that breathhold FRISK imaging improved spatial resolution of the data and maintained adequate temporal resolution compared with breathhold conventional imaging.Conclusion: FRISK, a new MRI sampling sequence that sparsely samples data and aligns acquired data during postprocessing, provides a scan time advantage of approximately a factor of 2 compared to conventional scans, and allowed rapid or breathhold scanning while obtaining acceptable accuracy.