Preliminary Assessment of Turbo Spectroscopic Imaging for Targeting in Brain Biopsy
Alastair J. Martina,
Haiying Liu
,a,
Walter A. Halla and
Charles L. Truwita
a From the Departments of Radiology (A.J.M., H.L., W.A.H., C.L.T.), Neurosurgery (W.A.H.), Radiation Oncology (W.A.H.), Neurology (C.L.T.), and Pediatrics (C.L.T.), University of Minnesota School of Medicine, Minneapolis; and Philips Medical Systems, Best, the Netherlands (A.J.M.).
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FIG 1.
A, Diagram shows the TSI pulse sequence. The initial 90° excitation pulse is followed by two 180° refocusing pulses, and each of these pulses is slice-selective in orthogonal directions. The signal from this selected volume is then phase-encoded and acquired (echo1). The phase encoding is rewound and the signal is then refocused, phase-encoded, and acquired again (echo2).
B, The third echo is acquired in an analogous way. K-space is filled in such that the first echoes fill in the inner third of k-space while the second echoes fill out the middle third, and the third echo fills out the outer third. Phase-encoding must be performed in two orthogonal directions (Kx, Ky), and thus a full signal acquisition occurs at each point on this Kx-Ky grid. Kx-Ky points lying outside the largest circle are not acquired to reduce imaging time
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FIG 2.
TSI findings in a 64-year-old man with a previously treated right parietal glioblastoma multiforme who presented with a rim-enhancing lesion.
A, Three representative spectra are shown from the locations indicated by the yellow stars on the corresponding images.
B and C, The spectroscopic volume is indicated (green line) on a coronal turbo-FLAIR image (B) and in-plane anatomic features are shown on an axial inversion-recovery scan (C).
D–G, Images reconstructed by integrating the area under the Cho (D), Cr (E), NAA (F), and lipid (G) peaks are shown with anatomic overlay contours extracted from the inversion-recovery image. The rim of the lesion exhibits enhanced Cho with corresponding reductions in Cr and NAA as compared with the reference spectrum (A). This is indicative of active tumor growth. The core of this lesion, however, reveals only a pronounced lipid peak, consistent with necrosis
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FIG 3.
37-year-old-man with a history of oligodendroglioma who had previously had a resection and received radiation therapy. He presented with three separate enhancing lesions and extensive surrounding edema.
A, Spectra were extracted that corresponded to the most posterior lesion (bottom spectrum), the middle lesion (middle spectrum), and the relatively normal contralateral hemisphere (top spectrum).
B–D, The reconstructed Cho (B) and lipid (C) maps are shown with anatomic contours extracted from an inversion-recovery image (D). Both lesions showed elevated Cho with reduced Cr and NAA. The most posterior lesion is likely more necrotic, as evidenced by lipid both on its spectra and in the corresponding region of the lipid image.
E–H, Immediately after preoperative imaging, a burrhole was created and trajectory alignment was accomplished. A contrast agent was administered, and T1-weighted imaging was performed during the alignment and biopsy processes. The central region of enhancement was selected for biopsy and an appropriately aligned trajectory guide was visible in oblique sagittal (E) and coronal (F) planes. These image planes were then monitored during the insertion of the biopsy needle to assure it reached the intended target (G and H)
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FIG 4. After appropriate positioning of the biopsy needle within the specified target, the patient was moved out the back end of the scanner and tissue samples were obtained. In this case, the biopsy needle was inserted through one of the two circular coils that constitute the interventional head coil (visible under the sterile drape). The in-room LCD displays used for aligning the trajectory guide and monitoring the needle insertion are visible in the background
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FIG 5.
TSI findings in a 38-year-old man in whom radiation injury was established on biopsy samples.
A–C, The location of an SVS volume is indicated on an axial inversion-recovery image (A) and a coronal T1-weighted image (B). The locations from which spectra were extracted from the TSI data are also shown on an inversion-recovery image (C).
D, The spectra (top, SVS results; middle, TSI of lesion; bottom, TSI from contralateral hemisphere for reference) show very low levels of Cho, Cr, and NAA, and indicate the presence of lactate within the lesion. Correspondence between the SVS and TSI data was considered to be very good. The lactate peak on TSI was substantially larger than on SVS, which was a common finding. The lactate peak appears as an inverted doublet on SVS and an unresolved positive peak on TSI as a result of differences in echo time and limitations in the TSI spectral resolution.
E–H, The spectral images obtained by integrating the area under the Cho (E), Cr (F), NAA (G), and lactate (H) peaks are also shown. Anatomic contours obtained from the inversion-recovery image (C) are overlaid
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FIG 6.
TSI findings in a 46-year-old woman with a large right parietal mass later confirmed to be an oligodendroglioma.
A–E, An inversion-recovery anatomic reference scan (A) shows the extent of the lesion. The intended site of the burrhole is indicated by an MR-visible surface marker (arrow, A). The Cho (B), Cr (C), NAA (D), and lipid (E) images are shown with anatomic contours extracted from the inversion-recovery image superimposed on them. Cho is enhanced and NAA is reduced throughout the lesion. Cr remains largely isointense throughout the brain and no appreciable levels or lipid are evident
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FIG 7.
A–E, SVS (A) and TSI (B) findings in a patient with a pathologically determined diagnosis of recurrent glioblastoma multiforme. An axial turbo-FLAIR image (C) shows the location from which the SVS data were acquired. The location from which the TSI data were extracted is shown on the reconstructed Cho image (D). Overlaid on the Cho image are contours extracted from an inversion-recovery image (E) acquired at the same spatial location. The patient had prominent lipid resonance and otherwise reduced metabolic levels on both SVS and TSI. While a modest degree of Cho elevation is evident on both spectra, it is difficult to definitively infer the presence of tumor
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