Phosphorus MRS of healthy human spleen

Abstract

Phosphorus (³¹ P-) MRS in vivo enables detection and quantification of important phosphorus-containing metabolites in biological tissues. ³¹ P-MRS of the normal spleen is challenging due to the relatively small volume and the larger distance between the spleen and surface coil. However, reference spectra of the healthy spleen are invaluable in studies of splenic malignancies and benign causes of splenomegaly, as well as in the study of its physiology. The purpose of this work was to investigate the feasibility of localized ³¹ P-MRS of healthy spleen in situ in a clinically acceptable measurement time using a clinical 3 T MR scanner. In this work, ³¹ P spectra of five healthy volunteers were measured using single-voxel image-selected in vivo spectroscopy (ISIS). The measurement sequence was augmented by broadband proton decoupling and nuclear Overhauser effect enhancement. It is demonstrated that localized ³¹ P-MRS of the spleen in situ using single-voxel ISIS is feasible on a clinical 3 T scanner in a clinically acceptable acquisition time. However, results have to be corrected for the transmitter excitation profile, and chemical shift displacement errors need to be taken into consideration during placement of the volume of interest. Results presented here could be used as a reference in future studies of splenomegaly caused by haematological malignancies.

Keywords: 3 T, feasibility; ISIS; healthy spleen; phosphorus MRS.

FIGURE 1

A typical voxel size (3 × 7 × 6 cm³) and position in axial and sagittal planes. A small water‐containing probe was attached to the centre of the coil on the outer side as a marker of coil position. Yellow rectangles show voxel positions corresponding to the carrier frequency of the transmitter. White rectangles depict voxel positions corresponding to PE (A), γ‐ATP (B), α‐ATP (C), and β‐ATP (D) spectral lines.

FIGURE 2

³¹P spectra of the spleens of five healthy volunteers. A Lorentzian apodization of the FIDs corresponding to 8 Hz line broadening was applied.

FIGURE 3

Summed spectrum of all volunteers (A), fitted spectrum (B), individual components (C), and residue (D). A Lorentzian apodization of the FIDs corresponding to 8 Hz line broadening was applied.

FIGURE 4

Excitation profile of the transmitter for a distance of 60 mm between the voxel centre and surface coil. Data were fitted by third order polynomial function (R ² = 0.99).