FASt single-breathhold 2D multislice myocardial T1 mapping (FAST1) at 1.5T for full left ventricular coverage in three breathholds

Abstract

Background: Conventional myocardial T₁ mapping techniques such as modified Look-Locker inversion recovery (MOLLI) generate one T₁ map per breathhold. T₁ mapping with full left ventricular coverage may be desirable when spatial T₁ variations are expected. This would require multiple breathholds, increasing patient discomfort and prolonging scan time.

Purpose: To develop and characterize a novel FASt single-breathhold 2D multislice myocardial T₁ mapping (FAST1) technique for full left ventricular coverage.

Study type: Prospective.

Population/phantom: Numerical simulation, agarose/NiCl₂ phantom, 9 healthy volunteers, and 17 patients.

Field strength/sequence: 1.5T/FAST1.

Assessment: Two FAST1 approaches, FAST1-BS and FAST1-IR, were characterized and compared with standard 5-(3)-3 MOLLI in terms of accuracy, precision/spatial variability, and repeatability.

Statistical tests: Kruskal-Wallis, Wilcoxon signed rank tests, intraclass correlation coefficient analysis, analysis of variance, Student's t-tests, Pearson correlation analysis, and Bland-Altman analysis.

Results: In simulation/phantom, FAST1-BS, FAST1-IR, and MOLLI had an accuracy (expressed as T₁ error) of 0.2%/4%, 6%/9%, and 4%/7%, respectively, while FAST1-BS and FAST1-IR had a precision penalty of 1.7/1.5 and 1.5/1.4 in comparison with MOLLI, respectively. In healthy volunteers, FAST1-BS/FAST1-IR/MOLLI led to different native myocardial T₁ times (1016 ± 27 msec/952 ±22 msec/987 ± 23 msec, P < 0.0001) and spatial variability (66 ± 10 msec/57 ± 8 msec/46 ± 7 msec, P < 0.001). There were no statistically significant differences between all techniques for T₁ repeatability (P = 0.18). In vivo native and postcontrast myocardial T₁ times in both healthy volunteers and patients using FAST1-BS/FAST1-IR were highly correlated with MOLLI (Pearson correlation coefficient ≥0.93).

Data conclusion: FAST1 enables myocardial T₁ mapping with full left ventricular coverage in three separated breathholds. In comparison with MOLLI, FAST1 yield a 5-fold increase of spatial coverage, limited penalty of T₁ precision/spatial variability, no significant difference of T₁ repeatability, and highly correlated T₁ times. FAST1-IR provides improved T₁ precision/spatial variability but reduced accuracy when compared with FAST1-BS.

Level of evidence: 1 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2020;51:492-504.

Keywords: MOLLI; T1 mapping; inversion recovery; multislice; myocardial tissue characterization; slice-selective.

Figure 1

FAST1 sequence diagram and acquisition scheme. Five T₁ maps are acquired in one breathhold, each based on a two‐heartbeat imaging block including a slice‐selective inversion pulse and the acquisition of two ECG‐triggered single‐shot images. Minimal inversion time is used for each imaging block to reduce the impact of cardiac motion between the slice‐selective inversion pulse and the first image acquisition. An inversion slice thickness larger than the imaging slice thickness is used to minimize the impact of cardiac motion. Recovery heartbeats are introduced between the third and fourth imaging blocks to minimize potential slice crosstalk between the slice‐selective inversion pulses. In the physiological HR range (50–110 bpm), the corresponding nominal breathhold duration is 9–13 sec.

Figure 2

Accuracy and precision of FAST1‐BS, FAST1‐IR, and MOLLI in numerical simulation. FAST1‐BS provided higher accuracy and reduced precision than FAST1‐IR and MOLLI. FAST1‐IR led to reduced accuracy and precision when compared with MOLLI. All techniques were T₂‐dependent.

Figure 3

Slice crosstalk using different T_RD and R_THK using FAST1‐BS and FAST1‐IR in phantom. (a) Maximum interslice T₁ variations among all vials using different T_RD from 4 sec to 10 sec and a fixed R_THK of 4. With T_RD exceeding 6 sec, maximum interslice T₁ variations were restricted to <13 msec. (b) Maximum interslice T₁ variations among all vials using different R_THK from 2 to 8 and a fixed T_RD of 6 sec. With R_THK not exceeding 4, maximum interslice T₁ variations were restricted to <11 msec.

Figure 4

T₁ accuracy (a), spatial variability (b), and repeatability (c) of FAST1‐BS, FAST1‐IR, and MOLLI in phantom. T₁ error was –26 ± 5 msec vs. –73 ± 53 msec vs. –56 ± 36 msec, T₁ spatial variability was 9 ± 6 msec vs. 8 ± 4 msec vs. 6 ± 4 msec and T₁ repeatability was 2 ± 1 msec vs. 1 ± 1 msec vs. 1 ± 0 msec, respectively.

Figure 5

Example native myocardial T₁ maps measured in one healthy volunteer using FAST1‐BS, FAST1‐IR, and MOLLI. Each row for FAST1‐BS and FAST1‐IR represents one FAST1 acquisition in a separated breathhold. Both FAST1 techniques enabled the acquisition of 15 contiguous slices covering the entire left ventricle in the same time as the acquisition of three slices using MOLLI (ie, 3 breathholds). Note the blue rectangles indicate the three common slice locations in FAST1 and MOLLI.

Figure 6

Native myocardial T₁ times (a), spatial variability (b), and repeatability (c) using FAST1‐BS, FAST1‐IR, and MOLLI in healthy volunteers. Average (bar plots) and SD (error bars) over all healthy volunteers are presented. FAST1‐BS, FAST1‐IR, and MOLLI provided different native myocardial T₁ times (P < 0.0001). FAST1‐BS and FAST1‐IR led to higher spatial variability than MOLLI (P < 0.001). There were no statistically significant differences between all techniques for T₁ repeatability (P = 0.18).

Figure 7

Segment‐wise native myocardial T₁ measures, spatial variability, and repeatability using FAST1‐BS, FAST1‐IR, and MOLLI in healthy volunteers. There were no statistically significant differences between all techniques in terms of segmental variations of native T₁ measures (P = 0.20), spatial variability (P = 0.32), and repeatability (P = 0.58).

Figure 8

Example native myocardial T₁ maps obtained using FAST1‐BS, FAST1‐IR, and MOLLI in a 31‐year‐old male patient admitted for suspected myocarditis. Each row for FAST1‐BS and FAST1‐IR represents one FAST1 acquisition in a separated breathhold. Both FAST1 techniques enabled the acquisition of 15 contiguous slices covering the entire left ventricle in the same time as the acquisition of three slices using MOLLI (ie, three breathholds). Note that the blue rectangles indicate the three common slice locations in FAST1 and MOLLI.

Figure 9

Example postcontrast myocardial T₁ maps obtained using FAST1‐BS, FAST1‐IR, and MOLLI in a 31‐year‐old male patient admitted for suspected myocarditis. Each row for FAST1‐BS and FAST1‐IR represents one FAST1 acquisition in a separated breathhold. Both FAST1 techniques enabled the acquisition of 15 contiguous slices covering the entire left ventricle in the same time as the acquisition of three slices using MOLLI (ie, three breathholds). Note the blue rectangles indicate the three common slice locations in FAST1 and MOLLI.

Figure 10

Pearson correlation and Bland–Altman analyses between FAST‐BS and MOLLI (a,c) as well as between FAST1‐IR and MOLLI (b,d) for both native and postcontrast myocardial T₁ times measured in both healthy volunteers and patients. In Pearson correlation analysis plots, confidence interval (solid lines) and identity line (y = x, dashed line) are also plotted besides the linear regression line (solid line). FAST1‐BS and FAST1‐IR yielded highly linearly correlated T₁ times with MOLLI (Pearson correlation coefficient = 0.93 for native and 0.98 for postcontrast myocardial T₁ times).