Influence of fat on liver T₁ measurements using modified Look–Locker inversion recovery (MOLLI) methods at 3T

Abstract

PurposeTo characterize the effect of fat on modified Look–Locker inversion recovery (MOLLI) T 1 maps of the liver. The balanced steady‐state free precession (bSSFP) sequence causes water and fat signals to have opposite phase when repetition time (TR) = 2.3 msec at 3T. In voxels that contain both fat and water, the MOLLI T 1 measurement is influenced by the choice of TR.Materials and MethodsMOLLI T 1 measurements of the liver were simulated using the Bloch equations while varying the hepatic lipid content (HLC). Phantom scans were performed on margarine phantoms, using both MOLLI and spin echo inversion recovery sequences. MOLLI T 1 at 3T and HLC were determined in patients (n = 8) before and after bariatric surgery.ResultsAt 3T, with HLC in the 0–35% range, higher fat fraction values lead to longer MOLLI T 1 values when TR = 2.3 msec. Patients were found to have higher MOLLI T 1 at elevated HLC (T 1 = 929 ± 97 msec) than at low HLC (T 1 = 870 ± 44 msec).ConclusionAt 3T, MOLLI T 1 values are affected by HLC, substantially changing MOLLI T 1 in a clinically relevant range of fat content. J. Magn. Reson. Imaging 2016;44:105–111.

Non-invasive assessment of portal hypertension using quantitative magnetic resonance imaging

“…Here, SE-EPI T 1 data were acquired with fat suppression, removing the effect of fat on the calculated liver T 1 value, which results from the water liver tissue compartment. In contrast, T 1 ∗ data acquired with a bFFE readout is affected by the hepatic fat content in a manner dependent on the phase between the fat and water signal (as determined by field strength and repetition time) [28]. Further since our T 1 measurement method is both respiratory triggered and multi-slice, it allows a large volume of the liver to be sampled [mean (± SD) of 3911 (± 1463) voxels covering 281 (± 106) cm 3 ] in a reasonable imaging time without the need for breath-hold, making this imaging scheme ideal for patient studies.…”

“…Previous studies using a modified look-locker inversion recovery (MOLLI) T 1 mapping method with bFFE readout have shown a correlation with fibrosis [22]. However, this technique requires a breath-hold for each slice acquired, and it has been shown that hepatic fat content can be large enough to cause severe MOLLI T 1 alterations [28]. The distribution of liver T 1 values (Gaussian FWHM) was also shown to increase with the worsening portal hypertension, reflecting the increasing heterogeneity of T 1 values across the liver volume.…”

Mapping tissue waterT1in the liver using the MOLLIT1method in the presence of fat, iron andB0inhomogeneity

“…The signal produced by bSSFP is dependent on the T 1 and T 2 of imaged proton species, flip angle and off‐resonance frequency . The frequency dependence, in particular, can result in complex behaviour of the bSSFP signal during T 1 recovery when the imaged voxels contain both fat and water . With typical imaging parameters and clinically relevant fat fraction, this leads to an overestimation of the liver water MOLLI T 1 , at odds with the decrease expected in a simple partial volume model.…”

“…This counterintuitive increase in MOLLI T 1 with fat is in addition to the effect of iron deposits that reduce T 1 and T 2 . Magnetization transfer, heart rate, repetition time of the bSSFP readout and B 0 inhomogeneity also influence MOLLI T 1 values.…”

Current and Future Magnetic Resonance Technologies for Assessing Liver Disease in Clinical and Experimental Medicine

“…Alternative approaches aim to correct T 1 by quantifying hepatic lipid content using localised cardiac-triggered proton spectroscopy in a selected region of interest [12] . However, this approach leaves T 1 vulnerable to hepatic fat interference [21] .…”