Endogenous assessment of chronic myocardial infarction with T_1ρ-mapping in patients

Background

Detection of cardiac fibrosis based on endogenous MR characteristics of the myocardium would yield a measurement that can provide quantitative information, is independent of contrast agent concentration, renal function and timing (van Oorschot et al. 2014). In ex vivo myocardial infarction (MI) tissue, it has been shown that a significantly higher T_1ρ is found in the MI region, and studies in animal models of chronic MI showed the first in vivo evidence for the ability to detect myocardial fibrosis with native T_1ρ-mapping (Witschey et al. 2012; Musthafa et al. 2012). In this study we aimed to translate and validate T_1ρ-mapping for endogenous detection of chronic MI in patients.

Methods

Patients

21 patients (19 M, 2 F, age 55 ± 9 years) underwent an MRI exam 2 to 12 months after clinically confirmed myocardial infarction. The study was performed on a Philips Achieva 1.5 T MR scanner (Philips Healthcare), using a 5-channel cardiac receive coil. Written informed consent was obtained from all patients.

In vivo MR: T_1ρ-mapping was performed using a T_1ρ-prepared balanced SSFP sequence. 4 images with different spin-lock preparation times (SL) with an amplitude of 750 Hz were acquired (SL = 1,13,27,45 ms). Bandwidth/pixel = 530 Hz, TE/TR = 1.94/3.9 ms, resolution = 1.5x1.65 mm, slice thickness = 6 mm, FOV = 288x288 mm², flip angle = 50 degrees, 2 TFE shots, NSA = 2, SENSE = 1.5. Images were acquired in late diastole during expiration breath holds, with an R-R interval of 3 beats. LGE MRI was performed 15 minutes after contrast injection (0.2 ml/kg contrast agent (Gadovist). (TI = 300-340 ms, TE/TR = 3.5/7.1 ms, resolution = 1.5x1.65 mm, slice thickness = 6 mm, FOV = 288x288 mm², flip angle = 25 degrees, 5 shots).

Analysis

T_1ρ-maps were calculated by pixelwise fitting of a mono-exponential decay function in Matlab (Mathworks). The LGE images and T_1ρ maps were scored using the 17 segments AHA-model.

Results

T_1ρ relaxation time was significantly higher in the infarct region (79 ± 11 ms), compared to healthy remote myocardium (54 ± 6 ms), p<0.0005. The myocardial region with an elevated T_1ρ relaxation time closely correlated with the corresponding LGE results (figure 1). Overlap in the scoring of scar tissue on LGE images and T_1ρ-maps was 74 % (table 1).

Figure 1

Short axis T_1ρ-maps with corresponding LGE images in 3 different patients. Arrows indicate the infarcted area.

Table 1 Score LGE versus T1ρ in patients with chronic MI (n=21), using the 17 segments AHA-model.

Conclusions

We have shown the feasibility of native T_1ρ-mapping for detection of infarct area in patients with a chronic myocardial infarction. Since this method is quantitative, requires no contrast agent, and thus is independent on renal function and timing, it may provide additional information or be an alternative to the LGE method in patients with severe renal failure.

Funding

N/A.