MicroSPECT/CT Unit

MicroSPECT

Single Photon Emission Computed Tomography (SPECT) is a well established clinical imaging modality. The microSPECT system for pre-clinical data acquisition is a clinical dual headed camera (e.cam, Siemens), equipped with pinhole collimators. The photons emitted by the subject enter the camera through the pinholes, available with diameters of 1 mm, 1.5 mm or 3 mm. The images are then enlarged on the detector, which enables imaging at a much higher resolution. This higher resolution has a price in terms of signal to noise ratio and field of view. These can be partially overcome by using multiple pinholes that increase the field of view with preservation of the resolution and sensitivity allowing whole body imaging. We currently use triple pinhole collimators with pinhole opening of 1 and 1.5 mm on both detector heads.

MicroCT

SPECT signals can be expressed in relative values (tumor to blood, signal to noise, etc.), however our imaging system allows for absolute image quantification (MBq) if 99mTc is used, by incorporating a triple energy window for scatter correction and co-registered CT derived attenuation maps for attenuation correction.

Co Bronnen

Image alignment between SPECT and CT is performed using fiducial markers: two acrylic circular disks containing three 3.7 MBq 57Co point sources incorporated in organic ion exchange beads of 1 mm diameter (Canberra, Zellik, Belgium). The disks measure 25 mm in diameter and 3 mm in thickness. The six beads provide reference points in both image modalities and are used as fiducial markers to generate a spatial transformation matrix.


For cardiac imaging “ECG gating” can be incorporated in the image protocol: combining the evaluation of myocardial perfusion and left ventricular function (ejection fraction, end diastolic volumes and end systolic volumes). During ECG gating, the cardiac cycle is divided into sixteen frames of the same duration, and the acquisition starts with the R wave. Images from several cycles are being stored separately in the computer and processed. During processing, all images of a particular frame are used to construct a specific phase of the cardiac cycle. Despite the challenges in imaging the small and fast contracting mouse heart, clear images can be made to automatically delineate infracted myocardial areas.


The most frequently used radio-label is 99mTc, followed by 111In and 123I. All image reconstructions are performed iteratively, based on the Ordered Subsets Expectation Maximization (OSEM) scheme including attenuation and scatter correction. Image processing is performed using A Medical Image Data Examiner (AMIDE).