Clinical feasibility of accelerated whole liver water T1 mapping with T2*-compensation

Abstract

Objective: Current liver T1 mapping methods present restricted liver coverage, take long acquisition times and mostly exclude the T1 bias induced by fat and iron effects. We evaluated the clinical feasibility of an accelerated water T1 (wT1) mapping method, including all liver segments and the potential of its T2*-compensation (wT1_comp) for fibrosis tissue assessment.

Materials and methods: Forty-three patients were classified into three groups: benign without/with risk of developing fibrosis and hepatocellular carcinoma (HCC). A 9-slice accelerated single-shot spiral continuous inversion-recovery Look-Locker (CIR-LL) wT1 mapping acquisition, performed in an 11-s breath-hold, and clinical images (proton density fat fraction (PDFF), T2*, T1- and T2-weighted) were acquired for all patients. ROIs were defined on the PDFF, T2* and wT1 maps in all liver segments. wT1_comp was estimated based on the wT1-T2* correlation of the benign-no-risk group and was compared to wT1 and clinical images inspecting for fibrosis.

Results: For each patient group, wT1 maps presented broad liver coverage, capturing all liver segments. T2* and wT1 measurements of the benign-no-risk group were significantly correlated $\left(\mathrm{wT}1=12.78*{T2}^{*}+481.45\mathrm{;\; r}=0.78,p<0.001\right)$ and the T2*-compensation model was defined by ${\mathrm{wT}1}_{\mathrm{comp}}=\mathrm{wT}1minus12.78*\left({T2}^{*}minus22\right)$ . Liver segments of the same patient presented different wT1 values. Outperforming wT1, wT1_comp identified 21 liver segments from nine patients associated with qualitative fibrosis findings in clinical images, some only visible in post-contrast T1-weighted images.

Conclusion: The wT1 method is feasible for fast broad liver coverage in patients with HCC or benign lesions. The segments-based wT1_comp analysis shows potential for noninvasive contrast-free qualitative liver fibrosis assessment.

Relevance statement: The proposed water-specific T1 mapping method, its T2*-compensation and the inclusion of all liver segments could be clinically relevant for the tissue signal assessment of fibrotic liver segments without contrast agent administration.

Key points: The developed water T1 (wT1) method enables broad liver coverage in a single 11-s breath-hold. Liver wT1 mapping and the proposed T2*-compensation (wT1_comp) remove the bias in T1 induced by fat and iron, respectively. The analysis in all liver segments allows the assessment of focal liver changes. The proposed liver segments-based wT1_comp method presents potential to identify tissue signal changes associated with fibrosis.

Keywords: Biomarkers; Carcinoma (hepatocellular); Liver fibrosis; Liver neoplasms; Magnetic resonance imaging.

Fig. 1

wT1 mapping methodology. Workflow to obtain the wT1 map of a slice. The CIR-LL acquisition is performed in 1.2 s, obtaining 100 undersampled spiral images (50 images × 2 TEs). After B₀-deblurring and water-fat separation, each 50-length water signal (fuchsia) is matched to a previously computed dictionary to estimate the value of the corresponding pixel in the wT1 map. CIR-LL, Continuous inversion recovery Look-Locker; TE, Echo time; TR, Repetition time; wT1, Water T1

Fig. 2

wT1 maps for the three groups in this study. 9-slice wT1 maps acquired in an 11 s breath-hold are shown for one patient in each group. a A 45-year-old woman with no pathology. b A 75-year-old woman with IPMN diagnostic, with no liver involvement and no signs of malignancy. c 74-year-old man with multifocal HCC depicted in great detail by the wT1 maps. HCC, Hepatocellular carcinoma; IPMN, Intraductal papillary mucinous neoplasm; wT1, Water T1

Fig. 3

ROI placement. The PDFF, T2* and wT1 maps of a 65-year-old patient of the benign-risk group with no evidence of malignancy are displayed. An ROI (white circle) was placed in every liver segment in the PDFF, T2* and wT1 maps. The nine wT1 maps are shown together with their anatomically corresponding PDFF and T2* maps. For this case, slice 5 and 6 represent the transition between liver segments; thus, no ROI was placed. Thanks to the availability of more slices, all liver segments could be located. The mean value of each ROI is displayed in the dark boxes. The mean value of the PDFF ROIs is higher than 5%; therefore, this case is considered part of the benign-risk group. PDFF, Proton density fat fraction; ROI, Region of interest; wT1, Water T1

Fig. 4

ROI analysis. wT1 versus T2* (first column), wT1_comp versus T2* (second column) and wT1_comp versus PDFF (third column) measurements are displayed for all groups. Liver segments of the same patient are displayed with the same marker. Based on the ${\mathrm{mean}}_{\mathrm{wT}1}$, ${\mathrm{SD}}_{\mathrm{wT}1}$, ${\mathrm{mean}}_{{\mathrm{wT}1}_{\mathrm{comp}}}$ and ${\mathrm{SD}}_{{\mathrm{wT}1}_{\mathrm{comp}}}$ of the benign-no-risk group (Table 2), upper and lower limits are defined (dashed lines). a Benign-no-risk group. b Benign-risk and (c) HCC patients with liver segments with low wT1 (${<\mathrm{mean}}_{\mathrm{wT}1}+1.96{\mathrm{SD}}_{\mathrm{wT}1}$), but high wT1_comp (${>\mathrm{mean}}_{{\mathrm{wT}1}_{\mathrm{comp}}}+1.96{\mathrm{SD}}_{{\mathrm{wT}1}_{\mathrm{comp}}}$) are highlighted (thick-edged marker). The remaining liver segments of these patients are shown with the same marker (thin-edged marker). HCC, Hepatocellular carcinoma; PDFF, proton density fat fraction; SD, Standard deviation; wT1, Water T1; wT1comp, T2*-compensated wT1

Fig. 5

A 62-year-old male with idiopathic granulomatous hepatitis. The T2-weighted image shows no abnormalities. Slight and mild T1 hyperintensity in S4a/b (arrow) is shown on the pre- and post-contrast T1-weighted image, respectively. Remarkably, the wT1 map reveals subtle, diffuse signal enhancement in S4a/b (arrow) without the use of a contrast agent. The wT1 and wT1_comp values of S4a/b (wT1_S4a = 814 ms, wT1_comp-S4a = 1,000 ms, wT1_S4b = 810 ms, wT1_comp-S4b = 960 ms) are represented as a thick-edged rhombus (right upper corner wT1 map) in Fig. 4b. wT1, Water T1; wT1_comp, T2*-compensated wT1

Fig. 6

A 73-year-old male with unifocal HCC in S6 (3.0 × 1.8 cm). The HCC (circle) shows hyperintensity on the T2-weighted image, hypointensity on the T1-weighted image and enhancement and washout after gadolinium contrast in the post-contrast T1-weighted image. Reticulations in S1 (arrow) appear post-contrast, with early arterial phase enhancement. On the wT1 map, scars in S1 (arrows) show prolonged T1 relaxation, detectable without contrast agent. The wT1 and wT1_comp values of S1 (wT1_S1 = 893 ms, wT1_comp-S1 = 988 ms) are represented as a thick-edged octagon (right upper corner wT1 map) in Fig. 4c. HCC, Hepatocellular carcinoma; wT1, Water T1; wT1_comp, T2*-compensated wT1

Fig. 7

A 77-year-old male with multifocal carcinoma. No hepatic alterations are seen on unenhanced T2- and T1-weighted images. After contrast administration, qualitative fibrosis signs appear in S3 (arrow), while wT1 maps detect scars (arrows) even without contrast application. The wT1 and wT1_comp values of S3 (wT1_S3 = 913 ms, wT1_comp-S3 = 960 ms) are represented as a thick-edged X (right upper corner wT1 map) in Fig. 4c. wT1, Water T1; wT1_comp, T2*-compensated wT1