SPECT low-field MRI system for small-animal imaging.
Localization of regions with increased uptake of radiotracer in small-animal SPECT is greatly facilitated when using coregistration with anatomic images of the same animal. As MRI has several advantages compared with CT (soft-tissue contrast and lack of ionizing radiation) we developed a SPECT/low-field MRI hybrid device for small-animal imaging.


METHODS
A small-animal single-pinhole gamma-camera (pinhole, 1.5 mm in diameter and 12 cm in focal length) adjacent to a dedicated low-field (0.1 T) small MR imager (imaging volume, 10 x 10 x 6 cm(3)) was used. The animal was placed in a warmed nonmagnetic polymethyl methacrylate imaging cell for MR acquisition, which was followed immediately by SPECT after translation of the imaging cell from one modality to the other. 3-Dimensional T1-weighted sequences were used for MRI. Phantom studies enabled verification of a low attenuation (10%) for (99m)Tc and (201)Tl and a very slight increase in Compton scattering due to the radiofrequency coil and polymethyl methacrylate imaging cell.


RESULTS
SPECT/MRI data acquisition and image coregistration of selected examples using different radiotracers for lungs, kidneys, and brain were obtained in 3 nude mice with isotropic spatial resolutions of 0.5 x 0.5 x 0.5 mm(3) for MRI and 1 x 1 x 1 mm(3) for SPECT. The total acquisition time for combined SPECT and MRI lasted 1 h 45 min.


CONCLUSIONS
A low-magnetic-field strength of 0.1 T is a simple and useful solution for a small-animal dual-imaging device combining pinhole SPECT with the adjacent MR imager.
Goetz
Christian
C
Service de Biophysique et Médecine Nucléaire, Hôpital de Hautepierre, Strasbourg, France.
Breton
Elodie
E
Choquet
Philippe
P
Israel-Jost
Vincent
V
Constantinesco
André
A
D000818:Animals; D001921:Brain / Q000000981:diagnostic imaging*; D007668:Kidney / Q000000981:diagnostic imaging*; D008168:Lung / Q000000981:diagnostic imaging*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods; D051379:Mice; D008819:Mice, Nude; D019047:Phantoms, Imaging; D013667:Technetium; D013794:Thallium Radioisotopes; D015899:Tomography, Emission-Computed, Single-Photon / Q000295:instrumentation* / Q000379:methods; D051598:Whole Body Imaging / Q000295:instrumentation / Q000379:methods
D013794:Thallium Radioisotopes; D013667:Technetium