Debbie Scandling

Diagnostic Performance of Treadmill Exercise Cardiac Magnetic Resonance: The Prospective, Multicenter Exercise CMR's Accuracy for Cardiovascular Stress Testing (EXACT) Trial

Background Stress cardiac magnetic resonance (CMR) has typically involved pharmacologic agents. Treadmill CMR has shown utility in single‐center studies but has not undergone multicenter evaluation. Methods and Results Patients referred for treadmill stress nuclear imaging (SPECT) were prospectively enrolled across 4 centers. After rest 99mTc SPECT, patients underwent resting cine CMR. In‐room stress was then performed using an MR‐compatible treadmill with continuous 12‐lead electrocardiogram monitoring. At peak stress, 99mTc was injected, and patients rapidly returned to the MR scanner isocenter for real‐time, free‐breathing stress cine and perfusion imaging. After recovery, cine and rest perfusion followed by late gadolinium enhancement acquisitions concluded CMR imaging. Stress SPECT was then acquired in adjacent nuclear laboratories. A subset of patients not referred for invasive coronary angiography within 2 weeks of stress underwent coronary computed tomography angiography. Angiographic data available in 94 patients showed sensitivity of 79%, specificity of 99% for exercise CMR with positive predictive value of 92% and negative predictive value of 96%. Agreement between treadmill stress CMR and angiography was strong (κ=0.82), and moderate between SPECT and angiography (κ=0.46) and CMR versus SPECT (κ=0.48). Conclusions The multicenter EXACT trial indicates excellent diagnostic value of treadmill stress CMR in typical patients referred for exercise SPECT.

Comparison of treadmill exercise stress cardiac MRI to stress echocardiography in healthy volunteers for adequacy of left ventricular endocardial wall visualization: A pilot study.

To compare exercise stress cardiac magnetic resonance (cardiac MR) to echocardiography in healthy volunteers with respect to adequacy of endocardial visualization and confidence of stress study interpretation.

Rapid assessment of quantitative T1, T2 and T2* in lower extremity muscles in response to maximal treadmill exercise

MRI provides a non‐invasive diagnostic platform to quantify the physical and physiological attributes of skeletal muscle at rest and in response to exercise. MR relaxation parameters (T1, T2 and T2*) are characteristic of tissue composition and metabolic properties. With the recent advent of quantitative techniques that allow rapid acquisition of T1, T2 and T2* maps, we posited that an integrated treadmill exercise–quantitative relaxometry paradigm can rapidly characterize exercise‐induced changes in skeletal muscle relaxation parameters. Accordingly, we investigated the rest/recovery kinetics of T1, T2 and T2* in response to treadmill exercise in the anterior tibialis, soleus and gastrocnemius muscles of healthy volunteers, and the relationship of these parameters to age and gender. Thirty healthy volunteers (50.3 ± 16.6 years) performed the Bruce treadmill exercise protocol to maximal exhaustion. Relaxometric maps were sequentially acquired at baseline and for approximately 44 minutes post‐exercise. Our results show that T1, T2 and T2* are significantly and differentially increased immediately post‐exercise among the leg muscle groups, and these values recover to near baseline within 30–44 minutes. Our results demonstrate the potential to characterize the kinetics of relaxation parameters with quantitative mapping and upright exercise, providing normative values and some clarity on the impact of age and gender. Copyright

Cardiopulmonary exercise testing in the MRI environment.

Maximal oxygen consumption ([Formula: see text]max) measured by cardiopulmonary exercise testing (CPX) is the gold standard for assessment of cardiorespiratory fitness. Likewise, cardiovascular magnetic resonance (CMR) is the gold standard for quantification of cardiac function. The combination of CPX and CMR may offer unique insights into cardiopulmonary pathophysiology; however, the MRI-compatible equipment needed to combine these tests has not been available to date. We sought to determine whether CPX testing in the MRI environment, using equipment modified for MRI yields results equivalent to those obtained in standard exercise physiology (EP) lab. Ten recreationally trained subjects completed [Formula: see text]max tests in different locations; an EP laboratory and an MRI laboratory, using site specific equipment. CMR cine images of the heart were acquired before and immediately after maximal exercise to measure cardiac function. Subjects in all tests met criteria indicating that peak exercise was achieved. Despite equipment modifications for the MRI environment, [Formula: see text]max was nearly identical between tests run in the different labs (95% lower confidence limit (LCL)  =  0.8182). The mean difference in [Formula: see text]max was less than 3.40 ml (kg/min)(-1), within the variability expected for tests performed on different days, in different locations, using different metabolic carts. MRI performed at rest and following peak exercise stress indicated cardiac output increased from 5.1  ±  1.0 l min(-1) to 16.4  ±  5.6 l min(-1), LVEF increased from 65.2  ±  3.3% to 78.4  ±  4.8%, while RVEF increased from 52.8  ±  5.3% to 63.4  ±  5.3%. Regression analysis revealed a significant positive correlation between [Formula: see text]max and stroke volume (R  =  0.788, P  =  0.006), while the correlation with cardiac output did not reach statistical significance (R  =  0.505, P  =  0.137). [Formula: see text]max CPX testing can be effectively performed in the MRI environment, enabling direct combination of physiological data with advanced post-exercise imaging in the same test session.

Myocardial function and perfusion assessment with exercise stress cardiovascular magnetic resonance using an MRI-compatible treadmill in patients referred for stress SPECT

Background Exercise stress cardiac magnetic resonance (CMR) has recently become feasible with the development of a fully MRI-compatible treadmill system along with improvements in imaging techniques. The utility of this setup has not been systematically compared with nuclear perfusion imaging. The study objective was to evaluate the accuracy and prognostic value of exercise stress CMR with a treadmill placed immediately next to the MRI scanner table in patients referred for treadmill stress nuclear perfusion imaging. Methods

Integrated treadmill stress testing and MR relaxometry (T1, T2, T2*): response in healthy calf muscles

Background Peripheral arterial disease (PAD) is accompanied by a complex lower limb pathophysiology resulting in reduced functional capacity and quality of life. We aim to characterize the exercise recovery kinetics in the calf muscle of healthy volunteers by combining treadmill exercise and magnetic resonance (MR) relaxometry (T1, T2 and T2*), and to investigate their relation with age and treadmill exercise duration.

Treadmill exercise stress cardiac MRI for the assessment of left ventricular wall motion: a comparison with stress echocardiography in healthy volunteers

Background Although exercise stress echo is commonly used for ischemic assessment, acoustic window limitations can often affect diagnosis. Recently, treadmill exercise stress CMR has become feasible (Foster et al, MRM, 2011); however, a direct comparison with stress echo has not been performed. The objective of this study was to compare exercise stress CMR to echo in healthy volunteers to assess left ventricular wall motion at peak stress.

Aortic Stenosis assessment with a 3-directional phase contrast magnetic resonance technique. Comparison to transthoracic echocardiography

Background Transthoracic Doppler-echocardiography (TTE) is the standard clinical method for diagnosis and staging of aortic stenosis (AS). AS staging is based on measurement of aortic peak velocity, transvalvular gradient, and calculation of aortic valve area. Unidirectional throughplane phase-contrast magnetic resonance imaging (1DPC-MRI) has been widely applied in clinical imaging to quantify aortic peak velocities and flow. Nonetheless, 1DPC-MRI requires accurate positioning of imaging planes perpendicular to flow direction in order to avoid peak velocity underestimation, which can be challenging in patients with multiple or eccentric jets. Therefore PC techniques with multi-directional velocity quantification would likely improve the accuracy of velocity determination, and allow for more accurate grading of AS severity. The aim of this study is to determine whether a rapid technique that is able to capture 3 directions of velocity in a 2D image plane in a single breath-hold (3DPCMRI) provides more accurate estimation of diagnostic parameters compared with the traditional 1DPC-MRI, using TTE as the reference standard.

Quantification of aortic stenosis diagnostic parameters: comparison of fast 3 direction and 1 direction phase contrast CMR and transthoracic echocardiography

BackgroundAortic stenosis (AS) is a common valvular disorder, and disease severity is currently assessed by transthoracic echocardiography (TTE). However, TTE results can be inconsistent in some patients, thus other diagnostic modalities such as cardiovascular magnetic resonance (CMR) are demanded. While traditional unidirectional phase-contrast CMR (1Dir PC-CMR) underestimates velocity if the imaging plane is misaligned to the flow direction, multi-directional acquisitions are expected to improve velocity measurement accuracy. Nonetheless, clinical use of multidirectional techniques has been hindered by long acquisition times. Our goal was to quantify flow parameters in patients using 1Dir PC-CMR and a faster multi-directional technique (3Dir PC-CMR), and compare to TTE.MethodsTwenty-three patients were prospectively assessed with TTE and CMR. Slices above the aortic valve were acquired for both PC-CMR techniques and cine SSFP images were acquired to quantify left ventricular stroke volume. 3Dir PC-CMR implementation included a variable density sampling pattern with acceleration rate of 8 and a reconstruction method called ReVEAL, to significantly accelerate acquisition. 3Dir PC-CMR reconstruction was performed offline and ReVEAL-based image recovery was performed on the three (x, y, z) encoding pairs. 1Dir PC-CMR was acquired with GRAPPA acceleration rate of 2 and reconstructed online. CMR derived flow parameters and aortic valve area estimates were compared to TTE.ResultsReVEAL based 3Dir PC-CMR derived parameters correlated better with TTE than 1Dir PC-CMR. Correlations ranged from 0.61 to 0.81 between TTE and 1Dir PC-CMR and from 0.61 to 0.87 between TTE and 3Dir-PC-CMR. The correlation coefficients between TTE, 1Dir and 3Dir PC-CMR Vpeakwere 0.81 and 0.87, respectively. In comparison to ReVEAL, TTE slightly underestimates peak velocities, which is not surprising as TTE is only sensitive to flow that is parallel to the acoustic beam.ConclusionsBy exploiting structure unique to PC-CMR, ReVEAL enables multi-directional flow imaging in clinically feasible acquisition times. Results support the hypothesis that ReVEAL-based 3Dir PC-CMR provides better estimation of hemodynamic parameters in AS patients in comparison to 1Dir PC-CMR. While TTE can accurately measure velocity parallel to the acoustic beam, it is not sensitive to the other directions of flow. Therefore, multi-directional flow imaging, which encodes all three components of the velocity vector, can potentially outperform TTE in patients with eccentric or multiple jets.

Diagnostic performance of treadmill exercise cardiac magnetic resonance: the prospective, multicenter EXACT trial

Methods Patients clinically referred for treadmill stress SPECT for the evaluation of known or suspected CAD were prospectively enrolled across 4 centers. After rest Tc99m SPECT imaging, patients underwent resting cine CMR. In-room stress was then performed using an MR-compatible treadmill with continuous 12-lead ECG monitoring and the Bruce exercise protocol. At peak stress, Tc99m was injected and patients were rapidly returned to their prior position in the magnet for real-time, free-breathing post-exercise cine and perfusion CMR. Following recovery monitoring with the table brought outside of the magnet bore, recovery cine and rest perfusion followed by late gadolinium enhancement acquisitions concluded the CMR portion of the exam. Stress SPECT images were then acquired in the adjacent nuclear laboratory. Patients not referred for invasive coronary angiography (ICA) within 2 weeks of stress imaging underwent coronary angiography with computed tomography (CTA). Diagnostic accuracy and prognostic value of treadmill stress CMR vs. SPECT were evaluated.