Temperature-corrected phantom T1/T2 mappings enable reliable multi-centre comparisons for long-term studies conducted in the Berlin CMR research network

Background: Parametric mapping in cardiovascular magnetic resonance (CMR) imaging is frequently used in both clinical practice and research to quantify myocardial tissue alterations. However, mapping values are influenced by various confounders such as scanner type and sequence parameters, which poses challenges for carrying out multi-center and prospective long-term studies (1). The T1 mapping and ECV standardization (T1MES) phantom was developed for quality assurance with tubes mimicking native and post-contrast mapping values of blood and myocardial tissue (2,3).



The AIM was to assess the stability of mapping values for long-term studies in the Berlin CMR research network to assure for quality.

Methods: The T1MES phantom was scanned quarterly from Q4/2022 to Q1/2025 at five CMR scanners (Site I-III: Siemens 3T, Site IV: Philips 3T, Site V: Siemens 1.5T) in the Berlin CMR research network (4) with three mapping sequences: T1 native (MOLLI 5(3)3), T1 post contrast agent (Site I-III,V: MOLLI 4(1)3(1)2, Site IV: MOLLI 5(3)3) and T2 (Site I-III,V: FLASH, Site IV: GraSE). One T1 post measurement (Q4/2022) was not performed at Site V. Temperature was measured for each timepoint. Postprocessing was conducted for each map and tube using an in-house software. The coefficient of variation (CoV) was calculated per sequence, site and tube to measure reproducibility and reported as mean ± standard deviation. Temperature corrections for T1 were based on established literature values for the T1MES phantom (3); T2 corrections were derived from reference measurements of an independent phantom (5). Linear regression models were plotted after temperature correction.

Results: For T1 native the CoV was 0.69 ± 0.45%, 1.00 ± 0.85%, 0.66 ± 0.43%, 0.68 ± 0.56% and 1.36 ± 0.48% for Site I-V respectively. For T1 post the CoV was 0.64 ± 0.49%, 0.8 ± 0.57%, 0.55 ± 0.36%, 0.46 ± 0.19% and 1.16 ± 0.50% for Site I-V respectively and for T2 the CoV was 1.7 ± 0.42%, 2.95 ± 1.10%, 2.02 ± 0.23%, 1.59 ± 0.37% and 3.27 ± 0.81% for Site I-V respectively (Tbl. 1). The tube mimicking native blood showed the highest variation for most sequences and sites. Temperature corrected T1 and T2 measurements remained stable over time with absolute slopes of < 0.5% per timepoint for T1 native and post contrast agent and < 0.75% per timepoint for T2, indicating an annual drift of less than 2% for T1 and less than 3% for T2. The linear regressions for the respective sequences can be seen in Fig. 1 on the example of normal myocardium and Fig. 2 on the example of blood pre and post contrast agent respectively. The slightly higher variation for T2 was expected as the phantom is optimized for T1 values, not T2.

Conclusion: The results of the linear regression analysis after temperature correction indicate stable and reliable reproducibility of T1 and T2 values over time. This enables comparison of mapping results of long-term studies conducted in the Berlin CMR research network.

Table 1: Coefficients of Variation (CoV) in percent per mapping sequence T1 MOLLI native, T1 MOLLI post contrast agent, T2, site and tube. Highlighted in green are CoV for tubes mimicking the native myocardium (myo) for T1 native and T2 and CoV for the tubes mimicking the myocardium post contrast agent for T1 post contrast agent.

	tube	Site I	Site II	Site III	Site IV	Site V
T1 native	myo native (short)	0.76	1.03	0.65	0.44	0.83
	myo native (medium)	0.93	1.49	1.03	0.69	1.21
	myo native (long)	1.11	1.86	1.09	1.10	1.71
	myo post (short)	0.30	0.22	0.18	0.10	1.43
	myo post (medium)	0.29	0.39	0.40	0.52	0.70
	myo post (long)	0.59	0.52	0.53	0.40	1.05
	blood native (normal)	1.50	2.52	1.33	1.85	2.31
	blood post (long)	0.38	0.33	0.22	0.46	1.38
	blood post (short)	0.41	0.66	0.52	0.31	1.12
	mean	0.69	1.00	0.66	0.68	1.36
	SD	0.45	0.85	0.43	0.56	0.48
T1 post contrast agent	myo native (short)	0.71	0.95	0.55	0.38	0.49
	myo native (medium)	0.78	1.08	0.89	0.48	1.06
	myo native (long)	1.16	1.40	0.88	0.56	1.71
	myo post (short)	0.22	0.28	0.17	0.13	1.45
	myo post (medium)	0.27	0.43	0.28	0.55	0.63
	myo post (long)	0.28	0.40	0.47	0.42	0.94
	blood native (normal)	1.63	1.91	1.19	0.83	1.90
	blood post (short)	0.36	0.38	0.16	0.45	1.51
	blood post (long)	0.34	0.38	0.40	0.31	0.76
	mean	0.64	0.80	0.55	0.46	1.16
	SD	0.49	0.57	0.36	0.19	0.50
T2	myo native (short)	2.01	2.65	1.87	1.81	3.49
	myo native (medium)	1.62	2.37	2.00	1.81	4.02
	myo native (long)	2.18	2.57	2.08	1.94	4.45
	myo post (short)	2.01	2.07	1.93	1.36	2.40
	myo post (medium)	1.87	2.43	1.78	1.72	3.14
	myo post (long)	1.73	2.01	2.18	1.68	2.49
	blood native (normal)	1.85	5.37	2.03	1.95	4.25
	blood post (short)	1.09	4.10	2.54	1.10	2.39
	blood post (long)	0.94	2.99	1.79	0.94	2.84
	mean	1.70	2.95	2.02	1.59	3.27
	SD	0.42	1.10	0.23	0.37	0.81

Figure 1: Linear regression for tubes mimicking medium myocardium (myo) pre (upper row) and post contrast agent (lower row) for T1 MOLLI native (left column), T1 MOLLI post contrast agent (pca, middle column) and T2 (right column) respectively. The individual sites are color-coded. Timepoints are given in the format year/quarter from the fourth quarter in 2022 to the first quarter in 2025.
Figure 2: Linear regression for tubes mimicking blood pre (middle row) and post contrast agent (upper row: long, lower row: short) for T1 MOLLI native (left column), T1 MOLLI post contrast agent (pca, middle column) and T2 (right column) respectively. The individual sites are color-coded. Timepoints are given in the format year/quarter from the fourth quarter in 2022 to the first quarter in 2025.