ABSTRACT
Purpose: The statistical quality of a PET scan can be significantly affected by the associated patient and scanner characteristics. Standard protocols could be optimized by regulating the administered activity Aadm such that the statistical quality is maximized for each individual patient for a given scan time. The objective is to model the direct relationship between the noise equivalent count rate NECR and Aadm for a wide range of scanner and patient parameters employed in clinical scans. Methods: A series of extensive and validated Monte Carlo simulations is utilized to systematically investigate, under realistic and controlled conditions, the effect of a wide set of [i] phantom sizes modeling children, slim and obese patients, [ii] bed positions, [iii] energy windows, [iv] coincidence time windows, [v] and combination of dead times and detector responses on the NECR for a range of Aadm. Results: A wide plateau is observed in NECR[Aadm] curves particularly for large patients, suggesting that 90-95% of peak NECR can still be obtained with considerably less Aadm. Moreover, for default scanner configurations and cardiac beds, an optimal Aadm range of 55-65 MBq for HR+ and 300-450 MBq for Biograph scanners, with the maximum NECR being considerably higher for the latter.Conclusions: The generalized NECR[Aadm] model can be utilized to predict for each individual Optimization, patient scan an optimal range of Aadm for which NECR is maximized, thus potentially allowing [a] for efficient utilization of the available activity in PET centers and [b] for minimization of cumulative radiation exposure
ABSTRACT
Purpose: Integrin alph beta is a promising imaging target of angiogenic activity which is up-regulated on activated but not on quiescent endothelial cells. Molecular imaging of alph beta integrin expression with the aid of a dedicated high resolution gamma camera, is a very sensitive imaging approach for the evaluation of angiogenesis in the rabbit hindlimb ischemia model. Furthermore, in order to evaluate the whole spectrum of endogenous process of collateralization after occlusion of an rtery, Digital Subtraction Angiography [DSA] was also used for the visualization of larger collaterals. Methods: The study included seven New Zealand White rabbits that underwent unilateral percutaneous endovascular embolization of the femoral artery, for the establishment of hindlimb ischemia that triggers the endogenous process of collateralization. The contralateral limb was not embolized and served as a control. The radiotracer that was employed for the angiogenesis imaging, was a 99 mTc labeled cyclic RGD peptide [[c RGDfk-His]-99mTc] that binds specifically to alph beta integrin via a three amino acid sequence [Arginine-Glycine-Aspartic acid or RGD]. Image acquisition was performed with a high resolution gamma camera and all animals underwent molecular imaging on the 3rd day and the 9th day post-embolization. In all animals DSA was performed on the 9th day post-embolization. Results: The acquired images demonstrated the retention of the radiotracer at the ischemic tissue is remarkably increased compared to the non-ischemic hindlimb [normal limb] [mean value 16020 +/- 2309 vs. 13139 +/- 2493 on day 3; p=0.0014 and 21616 +/- 2528 vs. 13362 +/- 2529 on day 9; p<0.0001, respectively. In addition, radiotracer retention in normal limbs seemeds to be increased at day 9 in normal limbs compared to day 3 [p=0.0112]. DSA demonstrated the mean vessel length detected was significantly superior in the normal compared to the ischemic limb at day 9 [mean value 3680 +/- 369.8 vs. 2772 +/- 267.7; p< 0.0001, respectively]. Conclusion: Angiogenesis was successfully detected using a 99 mTc labeled cyclic RGD peptide molecular imaging technique and was significantly more pronounced in the ischemic compared to normal limbs, both at 3rd and 9th days after embolization. The peak of the phenomenon was detected at 9?th days. Finally increased retention of radiotracer in normal limbs at day 9 indicates presence and gradual accumulation of activated endothelium in normal tissues as well
ABSTRACT
Combined PET/CT scanners now play a major role in medicine for in vivo imaging in oncology, cardiology, neurology, and psychiatry. As the performance of a scanner depends not only on the scintillating material but also on the scanner design, with regards to the advent of newer scanners, there is a need to optimize acquisition protocols as well as to compare scanner performances on an objective basis. In this study we evaluate and compare the performance of 4 Commercial GE PET/CT cameras, the [i] BGO-based Discovery ES PET/CT [DLS], [ii] the BGO-based Discovery ST PET/CT [DST], [iii] the BGO-based Discovery STE PET/CT [DSTE] and finally [iv] the EYSO-based Discovery RX PET/CT [DRX] scanner using the Geant4 Application for Tomographic Emission [GATE]. GATE is an open source Monte Carlo simulation platform developed for PET and SPECT studies and is supported by the OpenGATE collaboration. In accordance with the National Electrical Manufactures Association [NEMA] NU 2-2001 protocols, the validation of models is carried out against actual published measurements and the performance comparison is done for sensitivity, scatter fraction and count rate performance, showing very similar performance compared with published results, thus enabling investigations to better model system performance [e.g. resolution degradation] within the reconstruction task.. The simulated results demonstrate highest sensitivity performance with the DST [though with the highest scatter fraction], and highest NECR performance for the EYSO-based DRX, The results also show that DRX, DES and DSTE PET/CT cameras have nearly the same amount of scatter fraction