The role of preclinical SPECT in oncological and neurological research in combination with either CT or MRI

Abstract

Preclinical imaging with SPECT combined with CT or MRI is used more and more frequently and has proven to be very useful in translational research. In this article, an overview of current preclinical research applications and trends of SPECT combined with CT or MRI, mainly in tumour imaging and neuroscience imaging, is given and the advantages and disadvantages of the different approaches are described. Today SPECT and CT systems are often integrated into a single device (commonly called a SPECT/CT system), whereas at present combined SPECT and MRI is almost always carried out with separate systems and fiducial markers to combine the separately acquired images. While preclinical SPECT/CT is most widely applied in oncology research, SPECT combined with MRI (SPECT/MRI when integrated in one system) offers the potential for both neuroscience applications and oncological applications. Today CT and MRI are still mainly used to localize radiotracer binding and to improve SPECT quantification, although both CT and MRI have additional potential. Future technology developments may include fast sequential or simultaneous acquisition of (dynamic) multimodality data, spectroscopy, fMRI along with high-resolution anatomic MRI, advanced CT procedures, and combinations of more than two modalities such as combinations of SPECT, PET, MRI and CT all together. This will all strongly depend on new technologies. With further advances in biology and chemistry for imaging molecular targets and (patho)physiological processes in vivo, the introduction of new imaging procedures and promising new radiopharmaceuticals in clinical practice may be accelerated.

Fig. 1

State-of-the-art whole-body SPECT bone images acquired for 60 min with 250 MBq ^99mTc-HDP and with 0.25-mm resolution collimators (image courtesy of Oleksandra Ivashchenko, TU-Delft/MIlabs)

Fig. 2

Multimodality imaging of tumour uptake of targeted radiolabelled peptide and tumour perfusion. Rats bearing a syngeneic, somatostatin receptor overexpressing, neuroendocrine pancreatic tumour, were imaged by SPECT/CT and MRI to study tumour uptake of a ¹¹¹In-labelled somatostatin analogue ([¹¹¹In-DTPA]octreotide) and tumour perfusion by DCE-MRI respectively. Left Tumour perfusion depicted by the AUC value over the first 60 s as assessed by DCE-MRI; centre tumour uptake of radiolabelled [¹¹¹In-DTPA]octreotide of the same tumour section as imaged by MRI; right colour-coded overlay of the MR image and the SPECT image with MRI values depicted in red and SPECT values depicted in green. For correct image registration, MRI data were resampled to match the lower resolution of the SPECT/CT images (image courtesy of Joost Haeck and Karin Bol, Erasmus MC)

Fig. 3

Coronal, sagittal and transverse anatomical T1-weighted MRI scans coregistered with coloured subtraction SPECT data illustrating the changes in regional cerebral blood flow induced by deep brain stimulation (DBS). The white arrows indicate a DBS electrode artefact in the hippocampus. The corresponding sections, modified from the rat brain atlas of Paxinos and Watson [183] are shown on the right (CA1-CA3; DG dentate gyrus, Sub subiculum, Ent entorhinal cortex). The different hippocampal structures are coloured and the position of the DBS electrode is indicated (courtesy Tine Wyckhuys [131])

Fig. 4

Example of the principle of a transferable bed system. Left Schematic drawing of an animal bed with tailored interfaces for mounting into compatible cradles in SPECT and MRI scanners. Right Step-by-step photo representation of the transfer from a SPECT scanner to a MRI scanner: a at the end of SPECT/CT acquisition; b the animal bed is unplugged; c, d the animal and bed are moved towards the MRI scanner ; e, f the bed is docked and positioned inside the magnet followed by MRI acquisition (image courtesy of Philippe Choquet)

Fig. 5

Combined modality approaches. a Drawing of a SPECT/CT system in which the SPECT part can also image 511 keV photons to perform simultaneous SPECT/PET (from M.C. Goorden et al., JNM 2013). b, c Cross-sectional views of (b) a proposed SPECT/MRI system and (c) a SPECT/CT system. For b and c the SPECT system is placed in front while the MRI or CT system is placed at the back of the scanner (b, c courtesy of Mediso Medical Imaging Systems)

Fig. 6

Diagram of an integrated SPECT/CT system showing two SPECT detectors, a CT detector and an X-ray tube, all rotating on the same gantry (image courtesy of Siemens Healthcare)

Fig. 7

One of the commercial side-by-side solutions for integrating 1.5-T or 3-T MRI with SPECT and other modalities. In this example a robotic rotation/translation stage automatically transfers the animal between the systems. In this set-up the MRI system is integrated in line with the other modalities, while avoiding possible interference of the fringe magnetic field of the MRI system with the other modalities (image courtesy of MILabs B.V.)