Evaluation of iron overload by single voxel MRS measurement of liver T2

Abstract

Purpose:To overcome the difficulty of poor signal-to-noise ratio of magnetic resonance imaging (MRI) in evaluating heavy iron overload by using a single voxel magnetic resonance spectroscopy (MRS) technique. Materials and Methods:A single voxel STEAM pulse sequence with a minimum TE of 1.5 msec and a sampling volume of 36.6 cm 3 was developed and applied to 1/T2 measurement of the liver in 14 patients with thalassemia whose liver iron concentration was determined through biopsy. Results:The iron level ranged from 0.23 to 37.15 mg Fe/g dry tissue with a median value of 18.06. In all cases, strong MR signals were obtained. 1/T2 was strongly correlated with the liver iron concentration (r ϭ 0.95, P Ͻ 0.00005). Conclusion:The single voxel MRS measurement of T2 in liver iron overload overcomes the difficulty of lack of detectable signals in conventional MRI when the iron level is high. There is an excellent correlation between the iron level and 1/T2.

Accurate liver T measurement of iron overload: A simulations investigation and in vivo study

“…Signal intensity, S, was generated using the signal equation for a gradient-echo sequence. A longitudinal relaxation time of T 1 ϭ 586 ms for liver (24) was assumed, and MR parameters were chosen to correspond to two T* 2 multi-echo gradientecho sequences adopted in our institution for clinical assessment of liver iron: breath-held (TE ϭ [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Gaussian-distributed complex noise, with standard deviation noise , was added to the generated signal. Different signal-to-noise ratios (SNR ϭ M 0 / noise , where M 0 is the fully relaxed magnetization) in the range 20 to 300 were evaluated.…”

“…Thus, although the two model fits are theoretically identical under noiseless conditions, their divergence is apparent as SNR is reduced. Figure 2 compares the performance of all three curvefitting models using two different acquisition schemes (TE ϭ [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Fig. 2a) and echo spacing (min TE ϭ 1 ms), all models provide accurate R* 2 estimates.…”

“…In recent years, magnetic resonance imaging (MRI) has emerged as the most widely used noninvasive technique to quantify liver iron content, and correlation with biopsy results has been demonstrated (9 -11). To date, there have been many applications of MRI to study liver iron (12)(13)(14)(15)(16)(17), and several methods exist for acquiring and analyzing the MRI data. However, our understanding of how to optimize these procedures for accurate iron measurement needs to be improved.…”

Noninvasive measurement of iron: report of an NIDDK workshop

“…Note: Since the workshop was held, additional publications on theoretical 36,37 and practical [38][39][40][41] efforts to develop noninvasive methods for measurement of tissue iron have appeared and are cited here for ready reference. …”

Current and future applications ofin vitromagnetic resonance spectroscopy in hepatobiliary disease

“…An in vitro approach allows direct quantification of iron following MR analysis [42] . In vivo, Wang and colleagues demonstrated single voxel MRS measurement of T2 in liver iron overload that correlates strongly with iron quantification from biopsy and overcomes the difficulty of lack of detectable signals in conventional MRI [43] . Furthermore, Gandon and colleagues have proposed the use of a liver to muscle intensity ratio, which is transferable between equipment and sequences [44] .…”