Jason Craft

Variable density incoherent spatiotemporal acquisition (VISTA) for highly accelerated cardiac MRI.

For the application of compressive sensing to parallel MRI, Poisson disk sampling (PDS) has been shown to generate superior results compared with random sampling methods. However, due to its limited flexibility to incorporate additional constraints, PDS is not readily extendible to dynamic applications. Here, we propose and validate a pseudo‐random sampling technique that allows incorporating constraints specific to dynamic imaging.

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.

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.

Fast implementation for compressive recovery of highly accelerated cardiac cine MRI using the balanced sparse model.

Sparsity‐promoting regularizers can enable stable recovery of highly undersampled magnetic resonance imaging (MRI), promising to improve the clinical utility of challenging applications. However, lengthy computation time limits the clinical use of these methods, especially for dynamic MRI with its large corpus of spatiotemporal data. Here, we present a holistic framework that utilizes the balanced sparse model for compressive sensing and parallel computing to reduce the computation time of cardiac MRI recovery 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.

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.

The feasibility of combining low-level exercise with vasodilator stress in patients referred for stress perfusion cardiac MRI

Background Adenosine, an agonist of the A2a receptor, is widely used for stress CMR. However, target receptors for adenosine are heterogeneous in their location and facilitated physiologic effects. A2b and A3 receptors are responsible for bronchospasm and peripheral arteriolar vasodilation; A1 receptors are responsible for AV block. The rate of adverse reactions with adenosine approaches 80%, consisting of dyspnea, headache, flushing, chest/ abdominal discomfort, angina, ST depression, dizziness, nausea, and dysgeusia. In SPECT protocols, use of vasodilators has been previously established as safe during low level exercise, and results in fewer adverse reactions. Our hypothesis is that adenosine administered during low level exercise treadmill stress cardiac MRI is safe, feasible, and results in diagnostic quality imaging.

AN ELUSIVE QUEST TO EXPLAIN THE WORSENING “PULMONARY HYPERTENSION” IN A CASE OF KNOWN STABLE RESTRICTIVE VENTRICULAR SEPTAL DEFECT

Gerbode ventricular septal defect (VSD) is a rare communication between the left ventricle and right atrium. It is generally congenital in origin but on rare occasions is an acquired defect. Gerbode defect can either arise from a direct communication between LV and RA with an atrio-ventricular

Assessment of right ventricular function by treadmill exercise stress cardiovascular magnetic resonance in patients with repaired tetralogy of Fallot.

Cardiac MR (CMR) is considered the gold standard to assess right ventricular (RV) function in different scenarios, including cases of congenital heart disease. Moreover, an MR-compatible treadmill coupled with Real Time (RT) CMR has been developed for stress testing, and may be an optimal choice in this setting. The aims of this study were to determine the feasibility and accuracy of a RT CMR protocol to evaluate RV function at rest and after treadmill exercise in adults with history of repaired Tetralogy of Fallot (ToF).