Jay S. Detsky

Inversion‐recovery‐prepared SSFP for cardiac‐phase‐resolved delayed‐enhancement MRI

Delayed‐enhancement magnetic resonance imaging (DE‐MRI) can be used to visualize myocardial infarction (MI). DE‐MRI is conventionally acquired with an inversion‐recovery gradient‐echo (IR‐GRE) pulse sequence that yields a single bright‐blood image. IR‐GRE imaging requires an accurate estimate of the inversion time (TI) to null the signal from the myocardium, and a separate cine acquisition is required to visualize myocardial wall motion. Simulations were performed to examine the effects of a steady‐state free precession (SSFP) readout after an inversion pulse in the setting of DE‐MRI. Using these simulations, a segmented IR‐SSFP sequence was optimized for infarct visualization. This sequence yields both viability and wall motion images over the cardiac cycle in a single breath‐hold. Viability images at multiple effective TIs are produced, providing a range of image contrasts. In a study of 11 patients, IR‐SSFP yielded infarct sizes and left ventricular ejection fractions (LVEFs) similar to those obtained by IR‐GRE and standard SSFP, respectively. IR‐SSFP images yielded improved visualization of the infarct‐blood border because of the simultaneous nulling of healthy myocardium and blood. T  1* recovery curves were extracted from IR‐SSFP images and showed excellent qualitative agreement with theoretical simulations. Magn Reson Med 58:365–372, 2007.

MRI relaxation fluctuations in acute reperfused hemorrhagic infarction

MRI evaluations of intramyocardial hemorrhage in acute infarction have relied on T2 and T  2* shortening only. We propose a more comprehensive evaluation of hemorrhagic infarction based on the concept that fluctuations in T2 and T1 relaxation in acute reperfused infarction will reflect transient edema and hemoglobin oxidative denaturation to uncompartmentalized methemoglobin. Anteroapical infarction was created via percutaneous balloon in young swine (22–25 kg, N = 12). T2, T1, diastolic wall thickness (DWT), and the Gd‐DTPA partition coefficient (λ) were measured on days 0, 2, and 7. DWT was elevated at 1 hr postreperfusion (128% ± 53%, P = 0.0001), and alleviated on days 2 and 7 (48% ± 10%, P = 0.008; 53% ± 24%, P = 0.003). T2 and T1 elevations were coincident with early edema (ΔT2 = 55% ± 24%, P < 0.0001; ΔT1 = 27% ± 18%, P < 0.04). T2 and T1 were nearly normal on day 2 (ΔT2 = 8% ± 8%, P = 0.27; ΔT1 = 0% ± 1%, P = 0.65). On day 7, T2 increased while T1 decreased (ΔT2 = 27% ± 16%, P = 0.005; ΔT1 = −14% ± 10%, P = 0.02). λ was elevated by >150% at all time points (P ≤ 0.002). Histology verified hemorrhagic injury. T1 and T2 fluctuations are consistent with transient edema, as well as hemoglobin oxidative denaturation to decompartmentalized methemoglobin. This methodological development may broaden our understanding of hemorrhagic microvascular injury and improve its detection in clinical populations. Magn Reson Med, 2006.

Real-time Fourier velocity encoding: An in vivo evaluation

To compare in vivo real‐time Fourier velocity encoding (FVE), spectral‐Doppler ultrasound, and phase‐contrast (PC) magnetic‐resonance (MR) imaging.

Long-term tracking of bone marrow progenitor cells following intracoronary injection post-myocardial infarction in swine using MRI

Magnetic resonance imaging (MRI) can track progenitor cells following direct intramyocardial injection. However, in the vast majority of post-myocardial infarction (MI) clinical trials, cells are delivered by the intracoronary (IC) route, which results in far greater dispersion within the myocardium. Therefore, we assessed whether the more diffuse distribution of cells following IC delivery could be imaged longitudinally with MRI. In 11 pigs (7 active, 4 controls), MI was induced by 90-min balloon occlusion of the left anterior descending coronary artery. Seven (0) days [median (interquartile range)] following MI, bone marrow progenitor cells (BMCs) were colabeled with an iron-fluorophore and a cell viability marker and delivered to the left anterior descending coronary artery distal to an inflated over-the-wire percutaneous transluminal coronary angioplasty balloon. T2*-weighted images were used to assess the location of the magnetically labeled cells over a 6-wk period post-MI. Immediately following cell delivery, hypointensity characteristic of the magnetic label was observed in the infarct border rather than within the infarct itself. At 6 wk, the cell signal hypointensity persisted, albeit with significantly decreased intensity. BMC delivery resulted in significant improvement in infarct volume and ejection fraction (EF): infarct volume in cell-treated animals decreased from 7.1 +/- 1.5 to 4.9 +/- 1.0 ml (P < 0.01); infarct volume in controls was virtually unchanged at 4.64 +/- 2.1 to 4.39 +/- 2.1 ml (P = 0.7). EF in cell-treated animals went from 30.4 +/- 5.2% preinjection to 34.5 +/- 2.5% 6 wk postinjection (P = 0.013); EF in control animals went from 34.3 +/- 4.7 to 31.9 +/- 6.8% (P = 0.5). Immunohistochemical analysis revealed intracellular colocalization of the iron fluorophore and cell viability dye with the labeled cells continuing to express the same surface markers as at baseline. MRI can track the persistence and distribution of magnetically labeled BMCs over a 6-wk period following IC delivery. Signal hypointensity declines with time, particularly in the first week following delivery. These cells maintain their original phenotype during this time course. Delivery of these cells appears safe and results in improvement in infarct size and left ventricular ejection fraction.

Multicontrast late gadolinium enhancement imaging enables viability and wall motion assessment in a single acquisition with reduced scan times.

To determine the accuracy of multicontrast late enhancement imaging (MCLE) in the assessment of myocardial viability and wall motion compared to the conventional wall motion and viability cardiac magnetic resonance imaging (MRI) pulse sequences.

Papillary muscle involvement in myocardial infarction: Initial results using multicontrast late‐enhancement MRI

We hypothesized that multicontrast late‐enhancement (MCLE) MRI would improve the identification of papillary muscle involvement (PM‐MI) in patients with myocardial infarction (MI), compared with conventional late gadolinium enhancement (LGE) MRI using the inversion recovery fast gradient echo (IR‐FGRE) technique. Cardiac LGE‐MRI studies using both MCLE and IR‐FGRE pulse sequences were performed on a 1.5 Tesla (T) MRI system in 23 patients following MI. In all patients, PM‐MI was confirmed by the diagnostic criteria as outlined below: (a) the increased signal intensity of PM was the same or similar to that of adjacent hyper‐enhanced left ventricular (LV) infarct segments; and (b) the hyper‐enhanced PM region was limited to the PM area defined by precontrast cine images of steady‐state free precession (SSFP). Visual contrast score was rated according to the differentiation between LV blood pool and hyper‐enhanced infarct myocardium. Quantitative contrast‐noise ratios (CNR) of infarct relative to blood pool and viable myocardium were also measured on MCLE and IR‐FGRE images. Of these 23 patients, 13 studies demonstrated primarily involvement of the territories of the right coronary (RCA, 8 patients) and/or left circumflex (LCX, 5 patients) arteries and 10 involved the territories of left anterior descending artery (LAD) with some LCX involvement. Although both IR‐FGRE and MCLE determined the presence and extent of LV MI, better visual contrast scores were achieved in MCLE (2.9 ± 0.3) compared with IR‐FGRE (1.6 ± 0.8, P < 0.001). The CNRs of infarct relative to LV blood pool showed a significant statistical difference (n = 23, P < 0.00001) between MCLE (16.2 ± 7.2) and IR‐FGRE images (4.8 ± 4.1), which is consistent with the result of visual contrast scores between infarct and LV blood pool. The CNRs of infarct versus viable myocardium did not demonstrate a significant statistical difference (n = 23, P = 0.61) between MCLE (14.4 ± 7.0) and IR‐FGRE images (13.6 ± 6.1). MCLE clearly demonstrated PM‐MI in all cases (100%, 23/23) while only 39% ( 9/23 ) could be visualized on the corresponding IR‐FGRE images. In conclusion, MCLE imaging provides better contrast between blood pool and infarct myocardium, thus improving the determination of PM‐MI. J. Magn. Reson. Imaging 2011;33:211–216.

Free-breathing, nongated real-time delayed enhancement MRI of myocardial infarcts: A comparison with conventional delayed enhancement

To compare a free‐breathing, nongated, and black‐blood real‐time delayed enhancement (RT‐DE) sequence to the conventional inversion recovery gradient echo (IR‐GRE) sequence for delayed enhancement MRI.

MRI evaluation of microvascular obstruction in experimental reperfused acute myocardial infarction using a T1 and T2 preparation pulse sequence

To investigate a T1 and T2 preparation pulse sequence to evaluate microvascular obstruction (MO) in a porcine model of reperfused acute myocardial infarction (AMI).

Characterization of Post-infarct Scars in a Porcine Model --- A Combined Experimental and Theoretical Study

Arrhythmias are often associated with healing infarcts and could arise from the border zone of the scars. The main purpose of this work was to characterize the infarct scars using in vivo electro-anatomic CARTO maps (recorded in sinus rhythm) and high-resolution ex-vivo MR images in a porcine model of chronic infarct. The MR images were segmented into scar, peri-infarct and healthy ventricular tissue, and, in select slices, the results of segmentation were validated against histology. Further, the segmented volumes and associated fiber directions (derived from diffusion-weighted (DW) MRI as well as from synthetic models), were used as input to a simple two-variable mathematical model that calculates the propagation of depolarization waves and isochronal maps; and these isochronal maps were compared to the measured ones. We further correlated the size of the scar measured during the electrophysiology (EP) study with scar dimensions obtained from MRI using ex-vivo DW-MRI methods. Finally, we present preliminary results from a qualitative comparison between the scar delineation from ex vivo and in vivo MR images.

Should dexamethasone be standard in the prophylaxis of pain flare after palliative radiotherapy for bone metastases?—a debate

Pain flare is a well-recognized side-effect of palliative radiotherapy for the treatment of painful bone metastases, with recent randomized data showing incidence rates up to 35%. The impact of pain flare has been associated with worsening immobility, anxiety, depression and quality of life. The use of dexamethasone has recently been supported as an effective option in reducing radiation-induced pain flare based on the NCIC Clinical Trials Group (NCIC CTG) Symptom Control 23 (SC.23) randomized double-blind placebo-controlled trial. Despite this, conflicting opinions exist, and standard clinical use of dexamethasone to prevent pain flare continues to be debated among clinicians. Given this controversy, two sides of the debate are presented. Although consensus has not been achieved, the choice to use dexamethasone in the prophylactic setting to reduce pain flare incidence should be a shared decision between the oncologist and patient. Factors including symptom burden, comorbidities, performance status, quality of life and radiation dose and fractionation should be taken into account on an individualized level.