Editorial

Purpose: Dynamic myocardial perfusion (MP) PET imaging followed by tracer kinetic modeling allows quantification of myocardial blood flow, thus enabling computation of the coronary flow reserve, with considerable clinical potentials. Nonetheless, utilization of short dynamic frames can lead to noisy flow estimates, an issue that is further amplified in parametric imaging at the voxel level. Our purpose is to utilize an enhanced image reconstruction framework to better address this issue.
Methods: We implemented a novel 4D reconstruction scheme to directly estimate MP parametric images from the measured dynamic datasets. This included formulation of a 4D log-likelihood objective function relating the kinetic parameters to the projection datasets, and implementing numerical methods to optimize the objective function. We also utilized the technique of optimization transfer to enable more convenient and reliable parametric imaging. We simulated MP Rb-82 PET projection datasets based on the XCAT phantom utilizing patient-based time activity curves for the various organs and clinically realistic noise levels, followed by noise vs. bias analysis.
Results: The proposed direct 4D methodology was shown to outperform conventional indirect parametric imaging, reducing noise by over 50% (matched bias), with further reductions of15% in noise and a factor of five speed-up when optimization transfer was additionally utilized.
Conclusion: Direct 4D PET image reconstruction is a viable and very promising approach towards robust parametric MP PET imaging at the individual voxel level.

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 A(adm)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 A(adm)for a wide range of scanner and patient parametersemployed 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 A(adm).
Results: A wide plateau is observed in NECR A(adm)curves particularly for large patients,admsuggesting that 90-95% of peak NECR can still be obtained with considerably less A(adm) Moreover, for default scanner configurations and cardiac beds, an optimal A(adm)range of 55-65MBq for HR+ and 300-450 MBq for Biograph scanners, with the maximum NECR beingconsiderably higher for the latter.
Conclusions: The generalized NECR A(adm) model can be utilized to predict for each individual patient scan an optimal range of A(adm) 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.

Purpose: Integrin α β is a promising imaging target of angiogenic activity which is up-regulated on activated but not on quiescent endothelial cells. Molecular imaging of α β 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 artery, 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 α β 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 3 rd   and 9 th   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.

Purpose: Robotic camera holders have provided new prospects for more successful endoscopic surgeries. In this study we aimed to assess the operational subjective and objective outcomes of a newly developed camera holder, RoboLens, in comparison with a human camera holder, during laparoscopic ovarian cystectomy.
Methods: The study was performed as a randomized, single-blind, placebo-controlled, parallel-group trial. Forty patients with single ovarian cyst were randomized to laparoscopic ovarian cystectomy with robotic (RoboLens) or human camera holder.
Results: Results indicated that the surgeons felt less fatigue (P=0.047) and surgeries concluded sooner (P=0.001) in robotic assisted groups. Also, the image quality during operation with robotic camera holder was either superior or equal to what obtained with human assistant. However, mastery of the difficult situations, which were defined after the commencement of study, was significantly poorer in robotic group (P=0.001).
Conclusion: It was concluded that RoboLens, as a low cost robotic camera holder, is a safe, time and energy saving system which helps to obtain an improved vision from the surgery site.

Purpose: Glioblastoma Multiforme (GBM) brain tumor is heterogeneous in nature; so, its quantification depends on how to accurately segment different parts of the tumor, i.e. active tumor, edema and necrosis. This procedure becomes more effective when physiological information like diffusion-weighted-imaging (DWI) and perfusion-weighted-imaging (PWI) are incorporated with the anatomical MRI. In this preliminary tumor quantification work, the idea is to characterize different regions of the GBM tumors in an MRI-based multi-parametric approach to achieve more accurate characterization of pathological regions, which cannot be obtained by using individual modalities.
Methods: For this purpose, three MR sequences, namely T2-weighted imaging (anatomical MR imaging), PWI and DWI of five GBM patients were acquired. To enhance the delineation of the boundaries of each pathological region (peri-tumoral edema, tumor and necrosis), the spatial fuzzy C-means (FCM) algorithm is combined with the region growing (RG) method.
Results: The results show that exploiting the multi-parametric approach along with the proposed segmentation method can improve characterization of tumor cells, edema and necrosis in comparison to mono-parametric imaging approach.
Conclusion: The proposed MRI-based multi-parametric segmentation approach has the potential to accurately segment tumorous regions, leading to an efficient design of the treatment planning, e.g. in radiotherapy.

Purpose: Many of the available brachytherapy treatment planning systems in developing countries are not equipped with CT (or MRI) simulator; therefore, 3D treatment planning cannot be performed. In this project a new procedure has been introduced for utilizing the 2D digitally reconstructed radiograph from MRI images in brachytherapy treatment planning. This procedure enables us to localize the tumor volume and delineate the extent of critical structures in vicinity of tumor volume.
Methods: Pelvic lymph node chain position was delineated from transverse MRI images, and transferred into Digitally Reconstructed Radiograph (DRR) and then onto the X-ray images obtained from conventional simulator unit. These images were then imported to Brachytherapy treatment planning system to evaluate the dose to be applied to these organs in cervix Brachytherapy. The accuracy of the matching process was evaluated by phantom study, having known 3D geometric information and landmark assertion.
Results: The statistical variations obtained from distance mismatch in phantom and patient studies were in the range of clinically applicable error of registration (< 2mm). The results showed a large variation of the nodal dose when dose calculation is performed based on point B dose which is the geometrical reference point for calculating the dose to the pelvic lymphatic system. The result also shows that the dose to point B is usually underestimated to represent external iliac maximum dose, and overestimated for representation of external iliac minimum dose.
Conclusion: The results indicated that the DRR images can produce comparable accuracies in tumor localization reported in 3D MRI or CT based treatment planning procedures. Therefore, this technique could be used as a feasible approach where a 3D treatment planning is not available.

Purpose: In this work we present a handheld, solid-state detector based gamma camera system. We validated the camera physically and demonstrated the usefulness of the device for intra-operative detection of radiolabeled tissue.
Methods: We measured the intrinsic uniformity, the intrinsic energy resolution, the system uniformity, the spatial resolution without scatter, the system planar uniformity, the detector shielding and the peak deviation according to the NEMA NU1-2001 standard.
Results: The gamma camera can be used for isotopes with an energy range between 50-250 keV. A standard laptop is used to control of the camera and to visualize Preliminary clinical data show that the devices can be used successfully for a number of clinical applications.
Conclusion: The performance evaluation of a novel handheld gamma camera shows good spatial resolution, sensitivity and energy resolution. Due to the small size and weight the portable device can be used for untraoperative acquisitions.