T1 mapping of the myocardium: Intra-individual assessment of the effect of field strength, cardiac cycle and variation by myocardial region

Abstract

BackgroundMyocardial T1 relaxation time (T1 time) and extracellular volume fraction (ECV) are altered in the presence of myocardial fibrosis. The purpose of this study was to evaluate acquisition factors that may result in variation of measured T1 time and ECV including magnetic field strength, cardiac phase and myocardial region.Methods31 study subjects were enrolled and underwent one cardiovascular MR exam at 1.5 T and two exams at 3 T, each on separate days. A Modified Look-Locker Inversion Recovery (MOLLI) sequence was acquired before and 5, 10, 12, 20, 25 and 30 min after administration of 0.15 mmol/kg gadopentetate dimeglumine (Gd-DTPA; Magnevist) at 1.5 T (exam 1). For exam 2, MOLLI sequences were acquired at 3 T both during diastole and systole, before and after administration of Gd-DTPA (0.15 mmol/kg Magnevist).Exam 3 was identical to exam 2 except gadobenate dimeglumine was administered (Gd-BOPTA; 0.1 mmol/kg Multihance). T1 times were measured in myocardium and blood. ECV was calculated by (ΔR1myocardium/ΔR1blood)*(1-hematocrit).ResultsBefore gadolinium, T1 times of myocardium and blood were significantly greater at 3 T versus 1.5 T (28% and 31% greater, respectively, p < 0.001); after gadolinium, 3 T values remained greater than those at 1.5 T (14% and 12% greater for myocardium and blood at 3 T with Gd-DTPA, respectively, p < 0.0001 and 18% and 15% greater at 3 T with Gd-BOPTA, respectively, p < 0.0001). However, ECV did not vary significantly with field strength when using the same contrast agent at equimolar dose (p = 0.2). Myocardial T1 time was 1% shorter at systole compared to diastole pre-contrast and 2% shorter at diastole compared to systole post-contrast (p < 0.01). ECV values were greater during diastole compared to systole on average by 0.01 (p < 0.01 to p < 0.0001). ECV was significantly higher for the septum compared to the non-septal myocardium for all three exams (p < 0.0001-0.01) with mean absolute differences of 0.01, 0.004, and 0.07, respectively, for exams 1, 2 and 3.ConclusionECV is similar at field strengths of 1.5 T and 3 T. Due to minor variations in T1 time and ECV during the cardiac cycle and in different myocardial regions, T1 measurements should be obtained at the same cardiac phase and myocardial region in order to obtain consistent results.

Comprehensive Validation of Cardiovascular Magnetic Resonance Techniques for the Assessment of Myocardial Extracellular Volume

“…The small increase in ECV over time seen here (Figure 6), which is in keeping with the findings of Kawel et al 19 and Schelbert et al, 14 suggests that the 2-compartment model may be limited and an incomplete dynamic equilibrium between blood and myocardium is achieved. The lack of equilibrium may be because of penetration of gadolinium into other compartments, such as bone and synovial fluid, and because of faster renal clearance than exchange rate between compartments.…”

“…9,[14][15][16]18,19,39 Interestingly, ECV was significantly higher in the septum compared with other myocardial regions in healthy subjects. This is in keeping with histological data from healthy myocardium, which demonstrate higher collagen content in the septum compared with other regions, 40 and with DynEq-CMR data reported by Kawel et al 19 This finding, which may be secondary to the septum being exposed to mechanical strain from both ventricles, has important implications both in terms of CMR ECV measurement and histological assessment of CVF, as septal sampling seems not necessarily representative of other myocardial regions.…”

“…9,[14][15][16][17][18][19] In the second method, an isolated myocardial T 1 measurement is made at a fixed time point after a bolus of contrast agent (ie, without precontrast or blood T 1 measurements) and is used as a surrogate measure of ECV (isolated-T 1 ). [20][21][22][23] However, despite these techniques being applied to a rapidly expanding number of pathologies, both have potential shortcomings; the assumed dynamic equilibrium proposed in the first method may not always hold true in reality, and the second technique may be confounded by factors, such as body fat percentage, renal function, and hematocrit.…”

Cardiac MR Imaging to Probe Tissue Composition of the Heart by Using T1 Mapping

“…They studied 40 healthy volunteers (20 men, 20 women) using cardiac MR imaging. They found that left ventricular global and regional T1 times varied significantly between systole and diastole, which is in agreement with previous observations by Kawel et al (8). Diastolic values of T1 were slightly greater (by about 20 msec) than systolic T1 values; women had greater T1 values than men.…”

Diffuse Ventricular Fibrosis Is a Late Outcome of Tachycardia-Mediated Cardiomyopathy After Successful Ablation

“…Postcontrast T 1 time is known to be dependent on several factors including time postgadolinium infusion and renal function. 19,20 Because postcontrast timing of image acquisitions was progressively greater from the basal to the apical slices for each patient, a correction was applied to raw T 1 time results individually and according to modeling proposed by Gai et al 20 and to yield corrected T 1 time indexed for a postcontrast time of 15 minutes and an estimated glomerular filtration rate of 90 mL/min. For each subject, a single global corrected T 1 time was calculated by averaging the corrected T 1 times at each of the 3 short-axis slices.…”