Jeff A Stainsby

True T1 mapping with SMART1Map (saturation method using adaptive recovery times for cardiac T1 mapping): a comparison with MOLLI

Background SMART1Map is a new single-point technique for cardiac T1 mapping [1]. Unlike Look-Locker approaches, such as MOLLI, which yield an “apparent” T1 (T1*), SMART1Map directly measures true T1. Because T1* is a function of imaging parameters, it is always shorter than T1, and correction methods are required to obtain the true T1. This work compared the accuracy of SMART1Map with MOLLI in phantom experiments under several imaging conditions.

Myocardial T1 mapping using SMART1Map: initial in vivo experience

Background Recently a single-point, saturation-recovery myocardial T1 mapping sequence (SMART1Map = Saturation Method using Adaptive Recovery Times for cardiac T1 Mapping) was presented [1]. Compared to common methods like MOLLI, SMART1Map measures true T1 instead of apparent T1 relaxation, is more time efficient and can track exact TI times instead of estimated ones based on the heart rate during prescription. In this work we compare SMART1Map to MOLLI in an initial cohort of volunteers.

Comparing the accuracy and precision of SMART1Map, SASHA and MOLLI

Background Currently, MOLLI [1] is the most common method for measuring myocardial T1. Because MOLLI uses an SSFP-based Look-Locker approach, only the apparent T1 (T1*) can be measured, and there are concerns about the accuracy of the T1* values due to the dependence on imaging parameters. Alternatives to LookLocker imaging are single-point methods such as SASHA[2] and SMART1Map[3]. Although single-point methods are historically well-established and measure true T1, there remain differences between SASHA and SMART1Map that may affect their performance. Although both use single-point saturation recovery to acquire data at multiple saturation delay times (TS), the distribution of delay times is very different (Figure 1). The purpose of this work was to examine the accuracy and precision of MOLLI, SASHA, and SMART1Map in a phantom study.

Accelerated myocardial T1 mapping using SMART1Map and compressed sensing with temporal PCA

Background Myocardial T1 mapping has been proposed for characterizing a wide range of diffuse and focal fibrotic pathologies. Due to the demands of requiring multiple sample points along the signal relaxation curve in a breath-held ECG-gated scan, current T1 mapping methods have focused on single-shot acquisitions. Collecting all data in a quiescent time window has limited T1 mapping to a reduced number of k-space lines, often with parallel imaging. These compromises lead to low spatial resolution and/or low signal-to-noise (SNR) images. This work explores the initial feasibility of accelerating the recently proposed SMART1Map method[1] using Compressed Sensing with temporal Principle Component Analysis (CS-tPCA)[2] to obtain higher spatial resolution and higher SNR T1 maps.

Defining late onset occult asymptomatic cardiotoxicity in childhood cancer survivors exposed to anthracycline therapy: a cardiac magnetic resonance imaging study

Background There are over 270,000 childhood cancer survivors in the US. Of these survivors, more than 50% have been treated with anthracyclines and are at risk of developing progressive cardiotoxicity. Novel cardiac magnetic resonance imaging (CMRI) techniques are now able to reliably detect diffuse myocardial fibrosis and changes in regional myocardial function. We hypothesized that these novel CMRI techniques will identify occult asymptomatic cardiotoxicity in a cohort of childhood cancer survivors with normal global systolic function. Methods Twenty seven long-term childhood cancer survivors between 11.8-28.8 years with a cumulative dose >240mg/ m2 (mean 363±89) and normal systolic function (SF>29%) were studied 2.4-24 years after exposure to anthracycline therapy. Patients underwent CMRI techniques to characterize changes in T1 relaxation time, left ventricular myocardial peak circumferential and longitudinal strain parameters and were analyzed using the 17-segment model. Extracellular volume (ECV) was measured in 13 subjects all of whom were late gadolinium enhancement (LGE) negative. We performed standard CMRI assessment and quantification of myocardial mass, end-systolic and end-diastolic volumes, ejection fraction, and end systolic fiber stress. Results Twenty seven of 60 planned subjects have been imaged. End systolic fiber stress was significantly increased with higher cumulative anthracycline dose (R2=0.18, p<0.03) and younger age at diagnosis (R2=0.20, p<0.02). Lower average circumferential strain magnitude (ecc) and regional changes in peak circumferential strain were seen in multiple segments despite n ormal values of global systolic function by echocardiography and CMRI (Figure1). T1 maps are depicted in Figure 1. The mean T1 values of the myocardium were not significantly different between patients and controls at 4 min (375±67ms vs.389±36, p<0.07) and 10 min (433±52 ms vs.435±36, p<0.39), but were significantly lower at 20 minutes (455±50ms vs. 487 ±44, p<0.003) (Figure 2). Low myocardial T1 at 20 minutes was significantly associated with increases in end systolic fiber stress (R2=0.7, p<0.002). Higher mean ECV was observed in patients with cumulative dose ≥400mg/m2 (0.27 vs. 0.21, p<0.05). Conclusions

Exploring intrinsic MR signal relaxation in acute RF ablation lesions using T2 mapping and IR-SSFP CINE imaging

Background Cardiac MR has been used successfully in RF ablation therapies for arrhythmias, both for procedural planning and for post-ablation lesion imaging. Non-enhanced imaging, though it has a lower SNR, has advantages over Gdenhanced techniques mainly because contrast kinetics and dosage issues are avoided. Previously T2-weighted imaging was found to be more sensitive than T1-weighted imaging [1]. In this study, we performed non-enhanced T2 mapping and an inversion-prepared SSFP CINE imaging to characterize intrinsic relaxation behavior in acute lesions.

A comparison of methods for T2-mapping of the myocardium

Introduction T2-weighted imaging in acute myocardial infarction has been suggested for detecting regions of edema. The need to carefully account for variations in coil sensitivity patterns has been noted with these techniques. An alternate approach is to generate quantitative T2 maps. In this work we compare 3 different myocardial T2 mapping methods; multi-echo double-IR FSE (MEFSE), segmented T2-prepared SSFP (T2pSSFP) similar to [1] and T2-prepared spiral (SpiralT2) [2].

Myocardium T1 measurement using single and multi-shot SMART1Map acquisition: pros and cons

Background The recently published method SMART1Map[1] has proposed a new true T1 measurement technique. It consists in a 2D saturation-recovery prepared balancedSSFP sequence which allows different acquisition schemes depending on the number of repetition (shot) used. Single-shot acquisition duration is short but cardiac motion blur can occur due to long acquisition window duration. Two-shot acquisition time allows an acquisition window twice smaller but inter acquisition window motion can occur. Note that single-shot scheme allows to acquire an additional point when magnetization has not yet undergo any saturation pulse, thus corresponding to an infinite saturation delay time (T∞). In this study, we compared both schemes on healthy volunteers to determine the most appropriate strategy for a large range of T1 values measurement at 3T.

Robust fat saturation applied to late enhancement

Background Late Gadolinium Enhancement (LGE) allows imaging of infarction and cardiomyopathies by measuring the accumulation of contrast agent within the myocardium. The shortened T1 relaxation time compared to healthy myocardium is imaged by an inversion recovery (IR) prepared segmented fast gradient echo sequence in which pathology and fat show as bright signal. The fat signal can lead to misinterpretation and poor visualization of epicardial enhancement. In previous work fat was suppressed by using two appropriately timed fat-selective RF pulses which re-invert and invert fat signal [Foo et al., JMRI, 2007] but this technique was sensitive to off-resonance and heart rate variations. The goal of the present work is to make two improvements to fat-saturated LGE: (1) increase robustness against B0 and B1 variations by using asymmetric adiabatic RF pulses, and (2) increase robustness against heart rate variations through dynamic timing of fat-selective RF pulses.

T1, T2 and T2* mapping following acute myocardial infarction in a porcine model: Regional and serial alterations during infarct healing

Background Quantitative T1 and T2 cardiovascular magnetic resonance (CMR) approaches have been utilized to detect edema post acute myocardial infarction (AMI). However, a systematic comparison between the two measures is currently lacking. Furthermore, these relaxation measurements may also be confounded by opposing effects of intramyocardial hemorrhage that is typically not taken into account. The purpose of our study was to compare regional and serial fluctuations in T1 and T2 post-AMI and additionally quantify T2* that is a more specific marker of hemorrhage. Methods A porcine model of myocardial infarction was employed involving a 90 min LAD occlusion followed by reperfusion. Pigs (N=3) were imaged on a 1.5T scanner (GE Healthcare) in a healthy state (control) and at day 2 and week 4 post-AMI. The following sequences were utilized for quantification: T2 with multi-echo fast-spin-echo (4 echo’s; TE=5.6-105 ms); apparent T1 by modified look-locker with saturation recovery (TI=50-3000 ms); T2* by gradient echo (2 echo’s; TE=1.4, 15 ms; TR=18ms). Measurements were reported in two regionsof-interest (ROI): 1) infarct zone defined from late gadolinium enhancement images; and 2) remote uninfarcted myocardium. Two short-axis slices were analyzed for each study; the anatomical location was identical for all three sequences. Results Fig. 1 a shows the linear regression between T1 and T2 values when taken across all ROI’s and time points. Both T1 and T2 were significantly elevated at day 2 (p=0.0003, p=0.0001) and week 4 (p=0.01, p=0.005) post-AMI compared to control, respectively; see Fig. 1b and 1c. Reduced T2* at day 2 (p=0.05) suggested the presence of hemorrhage in all animals; see Fig. 1d. Percent change in T2 (relative to control) was significantly greater than that for T1 at both day 2 (25±12 vs. 13±3 %, p=0.05) and week 4 (62±36 vs. 20±13 %, p=0.03). A lower apparent change at day 2m ay be suggestive of influence from hemorrhage on both T1 and T2. Conclusions T1 and T2 are highly correlated in AMI; however, T2 is a more sensitive parameter to detect the underlying alterations following AMI. In the early sub-acute phase, both T1 and T2 may be affected by counteracting effects of edema and hemorrhage, unlike T2*. Furthermore, in the late phase when hemorrhage has resolved, sensitivity of T2 towards edema appears to be greater in comparison to T1; T1 may possibly be reduced due to chronic remodeling. Simultaneous characterization of these relaxation parameters may potentially offer useful insights into the complex remodeling processes that follow AMI.