Nuclear Medicine Gamma Camera Research Articles

SU-C-9A-02: Structured Noise Index as An Automated Quality Control for Nuclear Medicine: A Two Year Experience

Purpose: Flood-field uniformity evaluation is an essential element in the assessment of nuclear medicine (NM) gamma cameras. It serves as the central element of the quality control (QC) program, acquired and analyzed on a daily basis prior to clinical imaging. Uniformity images are traditionally analyzed using pixel value-based metrics which often fail to capture subtle structure and patterns caused by changes in gamma camera performance requiring additional visual inspection which is subjective and time demanding. The goal of this project was to develop and implement a robust QC metrology for NM that is effective in identifying non-uniformity issues, reporting issues in a timely manner for efficient correction prior to clinical involvement, all incorporated into an automated effortless workflow, and to characterize the program over a two year period. Methods: A new quantitative uniformity analysis metric was developed based on 2D noise power spectrum metrology and confirmed based on expert observer visual analysis. The metric, termed Structured Noise Index (SNI) was then integrated into an automated program to analyze, archive, and report on daily NM QC uniformity images. The effectiveness of the program was evaluated over a period of 2 years. Results: The SNI metric successfully identified visually apparent non-uniformities overlooked by the pixel valuebased analysis methods. Implementation of the program has resulted in nonuniformity identification in about 12% of daily flood images. In addition, due to the vigilance of staff response, the percentage of days exceeding trigger value shows a decline over time. Conclusion: The SNI provides a robust quantification of the NM performance of gamma camera uniformity. It operates seamlessly across a fleet of multiple camera models. The automated process provides effective workflow within the NM spectra between physicist, technologist, and clinical engineer. The reliability of this process has made it the preferred platform for NM uniformity analysis.

Radiation Exposure to Staff Using PET/CT Facility

Positron emission tomography (PET)combined with computed tomography (CT)has been playing key role in importantclinical decision-making in many areasever since its inception in the field ofmedical imaging. Most of the hospitals areenthusiastic for including PET/CT in theirimaging services because of its increasingapplication particularly in oncology.However, the occupational workers areapprehensive about the risk of higherradiation exposure in a PET/CT facilityeven more than that in conventional nuclearmedicine Gamma camera. There is a needtherefore to make the staff aware of theradiation doses they may likely get whileworking using this facility. We haveestimated the radiation exposure to thephysicians & technologists working in ourPET/CT facility based on the dose ratemeasurement with regularly calibratedpocket dosimeter and thermo-luminescentdetector (TLD); for cumulative doseconfirmation. The mean dose measured atthe chest level per PET/CT procedure was4 μSv and 4.75μSv for the physicians andtechnologists respectively. The mean doseto the physicians per MBq of 18F-FDGinjected was 10 nSv/MBq and 35 nSv/MBqat the chest and wrist levels respectively;whereas it was 12 and 25 nSv/MBq fortechnicians respectively

Suitability of nuclear medicine gamma cameras as gamma spectrometers in the event of a radiological emergency

Nuclear medicine gamma cameras are large area NaI(Tl) scintillation detectors that measure both the position and energy of incident gamma rays. A typical, commercial, large field-of-view (LFOV), gamma camera has about 2000 cm 3 of useful detector volume with an entrance window of 50×40 cm 2 by 1 cm thickness. A 3″×3″ NaI(Tl) detector, by comparison, has 17.4% of the volume and 2.3% of the area of the LFOV gamma camera. A 2002 survey reported 11,700 gamma cameras as being installed in hospitals and clinics in the US. In the event of a radiological emergency, the ability to utilize some of this installed detector capacity would be desirable. This work investigates the feasibility of using the gamma camera as a large area gamma spectrometer for detecting and quantifying isotopes likely to be involved in a radiological emergency caused by dispersion of radioactivity by a so called “dirty bomb.” Monte Carlo modeling was used to analyze detection sensitivity as a function of energy for the camera vs. the 3″×3″ cylinder. For a point source positioned 100 cm from the face of the detector, the ratio of total extrinsic efficiency of the camera to that of the 3″×3″ cylinder varied from 40.3 at 140 keV to 7.3 at 5 MeV. Ratios for extrinsic efficiency of peaks (including the full energy peak, single escape, and double escape peaks) varied from 41.1 at 140 keV to 5.5 at 5 MeV. Modifications that will be required to enable the cameras to function as spectrometers over a wide energy range are described and discussed. Given the large sensitivity advantage, the fact that the camera is shielded on three sides, and that cameras are already present at many locations to where victims of a disaster would be transported, it is desirable that such system capabilities be investigated.

An example of technological transfer to industry: the “IMI” project

Several INFN Sections and Departments of Physics of Italian Universities have spent many man-years in the attempt to adapt detector and read-out technologies, originally developed in the field of High Energy Physics, to the domain of biomedical apparatuses. The research covered such areas as the exploitation of crystals for the production of monochromatic X-ray beams, the development of devices for efficient X-ray detection, the design of advanced VLSI electronics, the improvement of Position Sensitive Photomultiplier Tubes and crystals for Nuclear Medicine gamma-cameras. These studies have been integrated in the Integrated Mammographic Imaging (IMI) project, funded by the Italian Government through the law 46/82 (art.10) and is carried on by five high-technology industries in Italy, namely LABEN, CAEN, AMS, GILARDONI and POL.HI.TECH. We report on the status of this technological transfer project.

Optimisation of the design of round-hole parallel collimators for ultra-compact nuclear medicine imaging

Hexagonal-hole parallel collimators are generally desirable over round-hole parallel collimators for most all medical imaging applications due to the optimum sensitivity offered by such a close-packed arrangement of apertures. However, such a sophisticated close-packed collimator arrangement is unlikely to adapt itself well to newly emerging, ultra-compact nuclear medicine gamma cameras. This is principally due to difficulties in machining and fabrication. In searching for alternative collimator designs, one must attempt, as far as possible, to preserve sensitivity, while optimising the spatial resolution achievable with the gamma camera. This work presents a general analysis of round-hole parallel collimator design for nuclear medicine imaging of 140 keV incident gamma-rays. Optimised designs are considered for a variety of source–collimator distances ( z=10, 20, 30, 40 mm) which represent typical sentinel node to collimator distances for our particular medical imaging application. Resolution and sensitivity characteristics are plotted as a function of collimator thickness and hole diameter. For each value of source–collimator distance, and for each collimator thickness investigated, the trade-off between sensitivity and spatial resolution is expressed as a series of characteristic curves.

A hybrid compliant vascular graft seeded with microvascular endothelial cells extracted from human omentum.

We report the development of a hybrid vascular graft using an innovative compliant poly(carbonate-urea)urethane unlike any previous polyurethane MyoLink as a permanent scaffold. The engineered graft has a hierarchical arterial structure: a monolayer of oriented microvascular endothelial cells (MVECs) and 3-D matrix (human collagen Type 4/dermatan sulfate) bonded onto MyoLink. The grafts' clinical feasibility was evaluated by determining optimal MVEC seeding density, incubation time, viability, and adhesion of these cells when exposed to arterial shear stress. MVECs from human omentum were isolated by a new centrifugation protocol, radiolabeled and seeded onto hybrid graft 2 to 18 x 105 cells/cm(2) for 24 h at 37 degrees C and for 1 to 5 h at 6 x 105 cells/cm(2), washed 3 times, and gamma counted. Qualitative assessment of seeding density/incubation was also undertaken with scanning electron microscopy (SEM) and viability tested with a modified Alamar Blue assay. A pulsatile flow phantom was used to subject the hybrid graft (200 mm length, 5 mm internal diameter) seeded with radiolabeled MVECs (6 x 105 cells/cm(2) at 2 h) to arterial shear and dynamic scintigraphy images acquired in real time using a nuclear medicine gamma camera system during 14 h of perfusion (n = 6). The optimal seeding density was 6 x 105 cells/cm(2), and qualitative SEM confirmed this. Incubating cells for 2 h produced significantly greater cell attachment than was seen for 1 h incubation (p < 0.05), and there was no significant difference in adhesion between cells incubated over the 2 h. Exposure of grafts to acute shear stress resulted in significantly higher proportions of initial cells attached to hybrid grafts compared to native MyoLink grafts (67 +/- 3% versus 55 +/- 2%, p < 0.001). As shown here, tissue engineering of native Myolink grafts significantly reduces the seeding density and incubation time to produce a monolayer onto which cells adhere to better.

Optimal Endothelialisation of a New Compliant Poly(Carbonate-Urea)Urethane Vascular Graft with Effect of Physiological Shear Stress

Objective: to define the optimal seeding conditions of a new stress free poly(carbonate-urea)urethane (CPU) graft with compliance similar to that of human artery with honeycomb structure engineered during the manufacturing process to enhance adhesion and growth of endothelial cells. Methods:111Indium-oxine radiolabeled human umbilical vein endothelial cells (HUVEC) were seeded onto CPU grafts at (a) concentrations from 2–24×105cells/cm2and (b) incubated for 0.5, 1, 2, 4 and 6 h. Following incubation, graft segments were subjected to three washing/gamma counting procedures and scanning electron microscopy (SEM). Cell viability was measured using a modified Alamar blueTMassay. To test physiological retention a pulsatile flow phantom was used to subject optimally seeded (16×105, 4 h) CPU grafts to arterial shear stress for 6 h with real time acquisition of scintigraphic images of seeded grafts using a nuclear medicine gamma camera system. Results: the seeding efficiency of 54±13% post three washes was achieved using 16×105cells/cm2. Similarly in SEM micrographs a seeding density of 16×105cells/cm2resulted in a confluent monolayer. Seeded CPU segments incubated for 4 h exhibited significantly higher resistance to wash-off than segments incubated for 30 min (p<0.05). Exposure of seeded grafts to pulsatile shear stress resulted in some cell loss with 67±3% of cells adherent following 6 h of perfusion with ongoing metabolic activity. Thus, optimal conditions were 16×105cells/cm2at 4 h. Conclusions: the optimal seeding conditions have been defined for ««tissue-engineered»» vascular graft which allow complete endothelialisation and high cell-to-substrate strength that resists hydrodynamic stress.

Development and evaluation of an ideal flow circuit: assessing the dynamic behavior of endothelial cell seeded grafts

The objective of this study was to develop and validate a flow system capable of simulating in vitro the pulsatile-flow waveform, pressures, and degree of oxygenation of physiological arterial circulation in vivo. We used this model to accurately determine endothelial cell adhesiveness on seeded vascular grafts exposed to physiological shear stress. The system consisted of a pulsatile-flow phantom capable of reproducing physiological arterial flow-including a reverse-flow component-which was filled with a nutritive, oxygenated solution that was of the same viscosity as whole blood. Real-time monitoring of all flow variables allowed continual adjustment of parameters and maintenance of physiological shear stress. To assess cell retention, human umbilical vein endothelial cells were radiolabeled with111indium, seeded onto compliant polyurethane vascular graft segments at a density of 1.8×106 cells/cm2, mounted in series with the flow circuit, and exposed to arterial shear stress for an 8-h period (n=6). Dynamic scintigraphy images were acquired in real time using a nuclear medicine gamma camera system during the 8-h perfusion period. The perfusion medium was tested for cytotoxicity, and the viability of seeded cells was assessed by Alamar Blue assay and scanning electron microscopy. Using the model, the shear stress and flow waveforms of human femoral arterial circulation were successfully simulated. The perfusate (viscosity 0.035 poise) was determined to be noncytotoxic. Postperfusion examination by scanning electron microscopy for known morphological indicators and Alamar Blue colorimetric assay for metabolic activity demonstrated normal cell appearance and activity. This system allows complete simulation of the hemodynamic variables encountered at the luminal surface of the femoral artery, while providing a nontoxic supportive milieu. Investigation of the behavior of seeded endothelial cells can be reliably and accurately undertaken with this system.

Nuclear Medicine Gamma Camera Malfunction May Pose Injury Risk

Nuclear Medicine Gamma Camera Malfunction May Pose Injury Risk

Adaptive Neural Network for Nuclear Medicine Image Restoration

A novel adaptive neural network is proposed for image restoration using a nuclear medicine gamma camera based on the point spread function of measured system. The objective is to restore image degradation due to photon scattering and collimator photon penetration with the gamma camera and allow improved quantitative external measurements of radionuclidesin-vivo . The specific clinical model proposed is the imaging of bremsstrahlung radiation using ^32P and^90 Y because of the enhanced image degradation effects of photon scattering, photon penetration and poor signal/noise ratio in measurements of this type with the gamma camera. This algorithm model avoids the common inverse problem associated with other image restoration filters such as the Wiener filter. The relative performance of the adaptive NN for image restoration is compared to a previously reported order statistic neural network hybrid (OSNNH) filter by these investigators, a traditional Weiner filter and a modified Hopfield neural network using simulated degraded images with different noise levels. Quantitative metrics such as the change of signal to noise ratio (ΔSNR) are used to compare filter performance. The adaptive NN yields comparable results for image restoration with a slightly better performance for the images with higher noise level as often encountered in bremsstrahlung detection with the gamma camera. Experimental attenuation measurements were also performed in a water tank using two radionuclides, ^32P and ^90 Y, typically used for antibody therapy. Similar values for an effective attenuation coefficient was observed for the restored images using the OSNNH filters and adaptive NN which demonstrate that the restoration filters preserves the total counts in the image as required for quantitative in-vivo measurements. The adaptive NN was computationally more efficient by a factor 4–6 compared to the OSNNH filter. The filter architecture, in turn, is also optimum for parallel processing or VLSI implementation as required for planar and particularly for tomographic mode of detection using the gamma camera. The proposed adaptive NN method should also prove to be useful for quantitative imaging of single photon emitters for other nuclear medicine tomographic imaging applications using positron emitters and direct X-ray photon detection.

Wavelet-based neural network with fuzzy-logic adaptivity for nuclear image restoration

A novel wavelet-based neural network with fuzzy-logic adaptivity (WNNFA) is proposed for image restoration using a nuclear medicine gamma camera based on the measured system point spread function. The objective is to restore image degradation due to photon scattering and collimator photon penetration with the gamma camera and allow improved quantitative external measurements of radionuclides in vivo. The specific clinical model proposed is the imaging of bremsstrahlung radiation using /sup 32/P and /sup 90/Y. The theoretical basis for four-channel multiresolution wavelet decomposition of the nuclear image into different subimages is developed with the objective of isolating the signal from noise. A fuzzy rule is generated to train a membership function using least mean squares to obtain an optimal balance between image restoration and the stability of the neural network, while maintaining a linear response for the camera to radioactivity dose. A multichannel modified Hopfield neural network architecture is then proposed for multichannel image restoration using the dominant signal subimages.