Myocardial perfusion imaging with a correlated X-ray CT and SPECT system: an animal study

Abstract

A bstractWe have performed a quantitative SPECT study in a porcine model of myocardial perfusion with the correlated X-ray CT traiismission and SPECT emission (ETCT) system developed at UCSF. Pixel values in the reconstructed SPECT images were calibrated in units of activity concentration and compared with the activity concentration determined from corresponding excised myocardial tissue samples. An object specific attenuation map was obtained by linear scaling from the X-ray CT. Attenuation maps with lower spatial resolution and higher signal to noise ratio were also derived from the X-ray CT image. The pixel Values and intensity distribution in reconstructed myocardial SPECT image was not sensitive to spatial resolution or noise in the transmission map for the given examples. An MLEM algorithm with regularization was used to determine mean and maximum pixel values for ROIs in the myocardial SPECT images. The use of the maximum pixel value did not sufficiently compensate for contrast degradation due to partial volume errors. A separate measurement of the myocardial wall thickness was used to adequately correct for partial volume errors.

Dual-Modality Imaging: More Than the Sum of its Components

“…Phantom experiments with this first prototype led to the development of a second prototype (Figure 3) having a 20-cm reconstruction diameter that could record emission and transmission data from stationary animal or object using a single HPGe detector array. Kalki et al 59,60 used this second prototype in animal studies both to demonstrate the capability of the system to facilitate image correlation and to test the feasibility of correcting the Figure 2. Schematic of data acquisition of combined emission-transmission imaging system developed at UCSF using single high-purity germanium detector array with fast pulse-counting electronics for simultaneous emission-transmission imaging.…”

“…Several methods have been described in the literature combining SPECT and MRI 91 and PET and MRI 92,93 for brain imaging, and SPECT and CT for cardiac and oncologic imaging. 21,59,69 Several approaches were developed specifically for quantitation using planar imaging 65,94,95 and are described in chapter 13 of this book. One technique called ''template projection'' 42,90 can be used to quantify radioactivity in planar images.…”

“…38,39,41,61 The major use of SPECT/ CT has been in reducing attenuation artefacts and improving the quality of myocardial perfusion imaging with 99m Tc-sestamibi. 21,59,[62][63][64] SPECT/CT also has demonstrated advantages for oncologic imaging with single-photon agents. 12,25,40,41,[65][66][67][68][69][70] Both SPECT/CT and PET/CT have demonstrated their ability to facilitate attenuation correction using an x-ray based patientspecific attenuation map that can be produced faster and more accurately than attenuation maps generated with external radionuclide sources.…”

“…108 SPECT/CT systems with a small segmented high-purity germanium detector operated in pulse-counting mode for simultaneous x-ray and radionuclide imaging. 23,26,57,59 A clinical prototype SPECT/CT system ( Figure 4) also was configured at UCSF by installing a GE X/RT SPECT camera and GE 9800 CT scanner in tandem with a common patient table, 21,22,42,69 and was used for studies on both large animals and patients. The first dual-modality imaging system designed for routine clinical use was the Millennium VG ( Figure 10) introduced by General Electric Healthcare Technologies (Waukesha, WI) in 1999.…”

Multi-modality imaging on track

“…The recognition of this problem led to the introduction of combined molecular and structural imaging devices: PET/ CT [4,5] and SPECT/CT [6,7]. SPECT/CT, originally suggested by Hasegawa and co-workers, predated PET/CT as an attempt to improve on the low-cost transmission scanning that was developed for cardiac attenuation correction (whose commercial implementation proved to be problematic [see 8]).…”