Coincidence Imaging Research Articles

Septa design for a prostate specific PET camera

The recent development of new prostate tracers has motivated us to build a low cost PET camera optimized to image the prostate. Coincidence imaging of positron emitters is achieved using a pair of curved detector banks. The bottom bank is fixed below the patient bed, and the top bank (which is above the patient) moves upward for patient access and downward for maximum sensitivity. In this paper, we study the design of septa for the prostate camera using Monte Carlo simulations. The system performance is measured by the detectability of a prostate tumor and by the conventional noise equivalent count (NEC). We have studied 27 septa configurations. The results show that septa design has a large impact on the lesion detection at a given activity concentration. At the background activity level of 0.1 /spl mu/Ci/cc, sparse septa with 8-crystal spacing outperforms the traditional two-dimension (inter-plane septa) and three-dimension (septaless) designs in terms of both the lesion detection and NEC. Significant differences are observed between the lesion detectability and NEC performance, indicating that the NEC may not be suitable for this lesion detection task.

Two- and three-body photodissociation of gas phase I(3) (-).

The photodissociation dynamics of I3- from 390 to 290 nm (3.18 to 4.28 eV) have been investigated using fast beam photofragment translational spectroscopy in which the products are detected and analyzed with coincidence imaging. At photon energies < or = 3.87 eV, two-body dissociation that generates I- + I2(A 3Pi1) and vibrationally excited I2- (X 2Sigmau+) + I(2P(3/2)) is observed, while at energies > or = 3.87 eV, I*(2P(1/2)) + I2- (X 2Sigmau+) is the primary two-body dissociation channel. In addition, three-body dissociation yielding I- +2I(2P(3/2)) photofragments is seen throughout the energy range probed; this is the dominant channel at all but the lowest photon energy. Analysis of the three-body dissociation events indicates that this channel results primarily from a synchronous concerted decay mechanism.

Femtosecond coincidence imaging of multichannel multiphoton dynamics.

The novel technique of femtosecond time-resolved photoelectron-photoion coincidence imaging is applied to unravel dissociative ionization processes in a polyatomic molecule. Femtosecond coincidence imaging of CF3I photodynamics illustrates how competing multiphoton dissociation pathways can be distinguished, which would be impossible using photoelectron or ion imaging alone. Ion-electron energy correlations and photoelectron angular distributions reveal competing processes for the channel producing (e(-)+CF+3+I). The molecular-frame photoelectron angular distributions of the two major pathways are strikingly different.

Incoherent coincidence imaging and its applicability in X-ray diffraction.

Entangled-photon coincidence imaging is a method to nonlocally image an object by transmitting a pair of entangled photons through the object and a reference optical system, respectively. The image of the object can be extracted from the coincidence rate of these two photons. From a classical perspective, the image is proportional to the fourth-order correlation function of the wave field. Using classical statistical optics, we study a particular aspect of coincidence imaging with incoherent sources. As an application, we give a proposal to realize lensless Fourier-transform imaging, and discuss its applicability in x-ray diffraction.

Dual-Head gamma camera coincidence imaging in pancreatic cancer

To assess the usefulness of dualhead camera imaging with 2-[fluorine-18]fluoro-2-deoxy- D-glucose (FDG) in the identification of malignant pancreatic lesions. Fifteen (15) patients with pancreatic masses (7 females and 8 males, mean age 52 ± 10 years) have been studied prospectively. After a 12-hour fasting patients received 120 MBq of FDG and were imaged in a dual-head camera equipped with coincidence detection. The final diagnosis was obtained by histology (biopsy or surgery in 13 patients) or follow-up (in 2 patients). Nine patients showed FDG uptake, all had pancreatic cancer proven on histological examination. Six patients had no tracer uptake: two had chronic pancreatitis, 1 had insulinoma, 1 had gastrinoma and two had pancreatic adenocarcinoma. Overall sensitivity was 69 %, specificity was 100 % and accuracy was 73%. Dual-head camera FDG images seem potentially useful in the characterization of the nature of pancreatic lesions. However, a negative study does not rule out malignancy in this patient population. Evaluar la utilidad de la realización de imagen con, 2-flúor-2 desoxi-D-glucosa-18F (FDG) em gammacámara de doble cabezal en la identificación de lesiones pancreáticas malignas. Hemos estudiado en carácter prospectivo 15 pacientes con masas pancreáticas (7 mujeres y 8 hombres, edad promedio 52 ± 10 años). Después de un ayuno de 12 horas los pacientes recibieron 120 MBq de FDG y equipada con detección por coincidencia. El diagnóstico final se obtuvo por histología (biopsia o cirugía en 13 pacientes) o por seguimiento (en 2 pacientes). Nueve pacientes mostraron captación de FDG, todos tuvieron cáncer pancreático probado con base en examen histológico. Seis pacientes no tuvieron captación del radiofármaco: dos pancreatitis crónicas, 1 insulinoma, 1 gastrinoma y dos adenocarcinomas pancreáticos. La sensibilidad global fue del 69 %, la especificidad fue 100 % y la exactitud fue del 73%. Las imágenes realizadas com FDG en cámara de doble cabezal equipada com detección por coincidencia parecen potencialmente útiles en la caracterización de lesiones pancreáticas, mientras que un estudio negativo no descarta totalmente malignidad.

Publisher’s Note: Quantum and Classical Coincidence Imaging [Phys. Rev. Lett.92, 033601 (2004)

Publisher’s Note: Quantum and Classical Coincidence Imaging [Phys. Rev. Lett.<b>92</b>, 033601 (2004)

VEGF-C induces collateral formation in ischaemic porcine heart model

VEGF-C has previously been shown to promote lympangiogenesis and mild angiogenesis. The aim of ths study was to investigate angiogenic potential of VEGF-C in ischaemic porcine heart model. Fifteen lanrace piglets were subjected to ameroid-induced gradual occlusion of the left circumflex artery. All animal treatment were performed conforming the 1991 revision of “Guiding Principles in the Care and Use of Animals”(American Physiological association). Three weeks after ameroid placement, 99Tc-sestamibi gated SPECT during rest and stress, in vivo angiography and gamma camera mounted dual head coincidence detection imaging were performed and the pigs were randomized to receive adeno (ad) VEGF-C (n = 6) or control adLacZ (n = 5). Four weeks later the examinations were repeated. At that time, in vivo angiography showed significantly greater collateral development in the (ad) VEGF-C group localized in the treatment area (p < 0,05) compared to the control group. Histology revealed more capillary vessels in the (ad) VEGF-C group versus control animals (p < 0,03).Coincidence detection imaging of 18F-FDG metabolism suggested improved myocardial viability in the treatment group compared to control animals (p = 0,054). SPECT perfusion imaging showed no difference between the groups. VEGF-C induces subtle, but statistically significant collateral formation in the ischaemic porcine heart model. The results suggest also better recognition of minor ischaemic changes in the myocardium using PET coincidence imaging versus SPECT.

Quantum and classical coincidence imaging.

Coincidence, or ghost, imaging is a technique that uses two correlated optical fields to form an image of an object. In this work we identify aspects of coincidence imaging which can be performed with classically correlated light sources and aspects which require quantum entanglement. We find that entangled photons allow high-contrast, high-resolution imaging to be performed at any distance from the light source. We demonstrate this fact by forming ghost images in the near and far fields of an entangled photon source, noting that the product of the resolutions of these images is a factor of 3 better than that which is allowed by classical diffraction theory.

The clinical impact of camera-based positron emission tomography imaging in patients with recurrent colorectal cancer.

F18-fluorodeoxyglucose (FDG)-positron emission tomography (PET) studies have clinical value in suspected recurrent or metastatic colorectal cancer cases. Because this modality is not accessible for many patients, a camera-based FDG (CB-FDG) coincidence imaging was suggested as an alternative. Although inferior in resolution to a dedicated PET system, it can make FDG studies available to more patients. We assessed the clinical value of CB-FDG in patients with recurrent colorectal cancer. The disease stage and treatment approach in 83 patients were twice determined by an oncologist and a surgeon, first based on the patient's records and blind to CB-FDG findings and then with the inclusion of FDG results in the decision-making analysis. On a lesion-based analysis, the sensitivity of CB-FDG was 95% and the specificity was 81% compared with 88% and 64%, respectively, for computed tomography. Adding FDG findings led to disease-stage alteration in 47 patients (57%), upstaging in 35 (42%), and downstaging in 12 (15%). FDG localized the tumor sites in 21 of 26 patients (81%) with suspected clinical recurrence and a negative conventional imaging workup. In 8 patients, FDG ruled out viable tumor tissue suggested by other modalities. The oncologist's suggested treatment approach was altered in 54% of the patients and the surgeon altered the decision on operability in 28%. CB-FDG assessment has clinical value for both staging and selecting treatment in patients with recurrent colorectal cancer and can be considered an alternative to an nonaccessible dedicated PET system.

Non-adiabatic intramolecular and photodissociation dynamics studied by femtosecond time-resolved photoelectron and coincidence imaging spectroscopy

Time-resolved photoelectron spectroscopy (TRPES) is emerging as a useful tool for the study of non-adiabatic dynamics in isolated polyatomic molecules and clusters due to its sensitivity to both electronic and vibrational dynamics. A powerful extension of TRPES, coincidence imaging spectroscopy (CIS), based upon femtosecond time-resolved 3D momentum vector imaging of both photoions and photoelectrons in coincidence, is a new technique for the study of complex dissociative processes. Here we show how these spectroscopies can be used to study both non-adiabatic intramolecular and photodissociation dynamics in polyatomic molecules. Intramolecular dynamics in the alpha, beta-enones acrolein, crotonaldehyde and methyl vinyl ketone are studied using both TRPES and laser-induced fluorescence of HCO(X) product yields. The location of the methyl group is seen to have very dramatic effects on the relative electronic relaxation rates and the HCO(X) yield. Applying both TRPES and CIS to the 200 nm and 209 nm photodissociation of the nitric oxide dimer, (NO)2, we observe the fs time-scale evolution of the excited parent neutral via its photoelectron spectrum and the emergence of the NO(A) photofragment including its energy and angular distributions.

Dual-Head gamma camera coincidence imaging in pancreatic cancer

To assess the usefulness of dual-head camera imaging with 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) in the identification of malignant pancreatic lesions. Fifteen (15) patients with pancreatic masses (7 females and 8 males, mean age 52 10 years) have been studied prospectively. After a 12-hour fasting patients received 120 MBq of FDG and were imaged in a dual-head camera equipped with coincidence detection. The final diagnosis was obtained by histology (biopsy or surgery in 13 patients) or follow-up (in 2 patients). Nine patients showed FDG uptake, all had pancreatic cancer proven on histological examination. Six patients had no tracer uptake: two had chronic pancreatitis, 1 had insulinoma, 1 had gastrinoma and two had pancreatic adenocarcinoma. Overall sensitivity was 69%, specificity was 100% and accuracy was 73%. Dual-head camera FDG images seem potentially useful in the characterization of the nature of pancreatic lesions. However, a negative study does not rule out malignancy in this patient population.

18F]Fluorodeoxyglucose Triple-Head Coincident Imaging as an Adjunct to 131I Scanning for Follow-Up of Papillary Thyroid Carcinoma

To evaluate the feasibility of using [(18)F]fluorodeoxyglucose ((18)FDG) triple-head coincidence imaging as a potential cost-effective alternative to positron emission tomography in the setting of suspected recurrence of papillary thyroid carcinoma. We retrospectively studied 10 patients with suspected recurrence of papillary carcinoma of the thyroid, who underwent (18)FDG coincidence imaging,(131)I scanning, and a reference anatomic scan (computed tomography, magnetic resonance imaging, or both) within 1 year in most cases. The (131)I scan detected the recurrence in five patients (62.5%) and failed to reveal recurrent cancer in three patients (37.5%); in contrast,(18)FDG imaging detected the recurrence in eight patients (100%) and was true negative in two patients in whom the scans were performed more than 1 year after effective therapy for the recurrence. The sensitivity of detection was unrelated to lesion size. The (18)FDG imaging results led to additional radiotherapy in all (131)I-negative patients, two of whom had high thyroglobulin levels and one of whom had a low thyroglobulin concentration but the presence of antithy-roglobulin antibodies. We conclude that (18)FDG triple-head coincidence imaging is useful for routine management of patients with thyroid cancer who have no abnormalities detected on (131)I scans but have high serum thyroglobulin levels. This technique, however, may not be as sensitive as a dedicated positron emission tomographic device, particularly for the assessment of small tumors.

Determination of three-dimensional voxel sensitivity for two- and three-headed coincidence imaging

Recently, SPECT and positron emission tomography imaging modalities have been hybridized so that positron coincidence detection can be accomplished with SPECT systems. Originally, only systems with two opposing camera heads were employed. Recent developments to improve sensitivity include the addition of a third camera head. Several authors have developed methods to calculate line-of-response and voxel sensitivities, known as rotational and geometric weights, respectively. These weights are important for use as normalization factors in iterative image reconstruction, as well as to provide insight into the nonuniformity of voxel sensitivity across the reconstructed field-of-view. Although their formulations use analytic expressions, the equations derived for the voxel sensitivities involve an integral which cannot be computed in closed form; that is, one must use a numerical approximation. This may affect the voxel sensitivity in that the accuracy and speed of such a discrete calculation are heavily dependent on the mesh size used. The authors' alternative approach, that does not rely on the numerical approximation, is to directly calculate the solid angle subtended by each voxel with the detectors over all detector positions. They include results for two camera heads 180/spl deg/ apart (DUAL), three camera heads 120/spl deg/ apart (TRI), and three camera heads 90/spl deg/ and 180/spl deg/ apart (C-SHAPE), with and without axial collimation.

Fast beam studies of I 2− and I 2− · Ar photodissociation

The photodissociation dynamics of bare I 2 − and I 2 − · Ar at 413 and 390 nm have been investigated using a fast beam instrument coupled with a new photofragment coincidence imaging detector. Results from the application of this technique to the dissociation of I 2 − and I 2 − · Ar yielded the dissociation energy of I 2 − ( D 0(I 2 −)=1.012±0.008 eV) and I 2 −–Ar binding energy ( D 0(I 2 −–Ar)=45±8 meV). The experiments show that at these wavelengths, I 2 − · Ar undergoes three-body dissociation to I − + I* + Ar, with very low momentum in the Ar atom and unequal momentum partitioning between the two I atoms.

Impact of technology on the utilisation of positron emission tomography in lymphoma: current and future perspectives.

Positron emission tomography (PET) has now gained a place in the management of patients with cancer, including those with Hodgkin's disease and non-Hodgkin's lymphoma. Restaging studies and those addressing the monitoring of response to treatment are especially in focus. Most of the knowledge gained has been achieved with dedicated BGO-based PET technology, but there are a number of developments that will impact on the use of this metabolic imaging technique in the investigation of patients with lymphoma. The challenges ahead are determined by the need for high-quality whole-body imaging associated with increased patient throughput and the need to investigate the role of new labelled ligands. The latter are likely to yield new insights into tumour cell characterisation, tumour behaviour and tumour outcome assessment. The study of new radiolabelled ligands will impose further demands for rapid dynamic data acquisition and accurate tracer quantification. Current and future developments in PET technology range from the use of new detector materials to different detector geometries and data acquisition modes. The search for alternatives to BGO scintillation materials for PET has led to the development of PET instruments utilising new crystals such as LSO and GSO. The use of these new detectors and the increased sensitivity achieved with 3D data acquisitions represent the most significant current developments in the field. With the increasing demands imposed on the clinical utilisation of PET, issues such as study cost and patient throughput will emerge as significant future factors. As a consequence, low-cost units are being offered by the manufacturers through the utilisation of gamma camera-based SPET systems for PET coincidence imaging. Unfortunately, clinical studies in lymphoma and other cancers have already demonstrated the limitations of this technology, with 20% of lesions <15 mm in size escaping detection. On the other hand, the recent development of combined PET/CT devices attempts to address the lack of anatomical information inherent with PET images, taking advantage of further improvement in patient throughput and hence cost-effectiveness. Preliminary studies using this multimodality imaging approach have already demonstrated the potential of the technique. Although the potential exists, certain technical issues with PET/CT require refinement of the methodology. Such issues include organ movement (such as respiratory motion), which strongly influences the image fusion of a rapidly acquired CT scan with the slower acquisition of a PET dataset, and the derivation of CT-based attenuation coefficients in the presence of contrast agents or metallic implants. The application of the technology for radiotherapy planning also poses a number of associated challenges. Finally, the development of dedicated PET systems based on planar detector arrangements with new detector components has the potential to improve clinical throughput by over 100%, but clinical trials using such systems have still to be carried out in order to establish the associated whole-body image quality.

A new pileup-prevention front-end electronic design for high-resolution PET and gamma cameras

A new method for processing signals from Anger position-sensitive detectors used in gamma cameras and positron emission tomography (PET) is proposed for very high count-rate imaging. It has a same concept as high yield pileup-event recover (HYPER) method we introduced before by using 1) dynamically integrating a present event, the integrating will stop immediately before the next event is detected; 2) estimating a weighted-value to indicate the total energy inside the scintillation detector; and 3) remnant correction to remove the residual energy of all the previous events from the weighted-value. This paper introduces two improved practical techniques to get a better weighted-value with low noise sensitivity in order to improve the final pileup-free energy resolution. One applies a low-pass filter combined with multiple sampling to a weight-sum of the instantaneous signal and integrated signal. The other one is weighting the integration value of the income signal; the weighting also includes exponential distortion compensation. This paper also describes the application of the HYPER electronics in a high resolution low cost PET camera with 12 photomultipliers (PMTs)-quadrant-sharing (PQS) detector modules that can decode 38 016 bismuth-germinate (BGO) crystal elements using 924 PMTs. Each detector module has four Anger-HYPER circuits to further increase the count-rate. To use the HYPER circuit in coincidence imaging applications, there is a serious synchronization problem between the arrival time of an event and the end time of integration that is variable from event to event. This synchronization problem is solved by a field programmable gate array (FPGA) circuit with real time remnant correction and a high-resolution trigger delay unit with a small dead-time for recovering the synchronization of data and the event-trigger.

Dynamic and static tomographic renal coincidence imaging with a gamma camera using Rb-82: a feasibility study

Rb-82, a positron emitter with a half-life of /spl sim/75 s, is a promising radionuclide that can potentially turn the concept of sequential dynamic tomographic renal imaging into reality. In this preliminary investigation, we explored several aspects of renal imaging with Rb-82 on a hybrid single photon emission computed tomography (SPECT)-positron emission tomography (PET) system, which relate to the feasibility of such imaging. First, the resolution of Rb-82 was approximated using the Deluxe ECT phantom with solid spheres (0.95 to 3.18 cm in diameter) and compared with Tc-99m. In addition, the impact of spatial resolution was assessed in-vivo in terms of the visualization of wax objects placed in the kidneys. Furthermore, the possibility of performing dynamic and static tomographic Rb-82 renal imaging was explored. A single 3-mCi Rb-82 bolus and limited angle tomography were used for dynamic imaging, while multiple bolus infusions in combination with either single- or multiple-step acquisitions were used for static imaging. Renal acquisitions were done using New Zealand White Rabbits weighing between 4 and 7 kg. Similar visualization of the cold spheres was noted in the phantom, and better visualization of the wax inserts was noted in the in vivo study for Rb-82 compared to Tc-99m. With decay and resolving time loss correction, the limited-angle dynamic tomographic studies showed the kidneys to have the highest uptake of any organ by 20-30 s. The renal uptake continued to increase up to 120-150 s when it became approximately constant. This significant and relatively constant renal uptake of Rb-82 allowed full tomographic imaging of the kidneys to be performed with multiple bolus infusions. In conclusion, we showed that it is possible to do dynamic renal imaging and due to the short half-life, acquisitions can be repeated every 7 min. This gives the clinician a powerful tool to track changes in the kidney over short intervals.

PET imaging using a triple-head gamma camera.

Interest in clinical fluorodeoxyglucose (FDG) imaging with multiple-head gamma cameras is growing. To improve sensitivity, triple-head coincidence imaging has been proposed. We report our initial experiences with a triple-head coincidence gamma camera with 19 mm sodium iodide crystal thickness. Several positron emission tomography-image quality parameters were evaluated using a Carlson and line source phantom. The system sensitivity with two-dimensional axial shields was 830 cps kBq-1 ml-1 and maximum noise equivalent count rate 1900 cps for an 18F-activity of 50 MBq. The imaging resolution was in central axial 7.0 mm and in central transaxial 7.6 mm, respectively. The average scatter fraction in scattered media was 29%. Clinical brain, heart and whole body images studies with [18F]FDG were acquired and they show good correlation with the phantom image quality. As a conclusion, triple-head coincidence gamma camera provides relatively high-count rate imaging with good contrast and resolution.

“Two-Photon” Coincidence Imaging with a Classical Source

Coincidence imaging is a technique that extracts an image of a test system from the statistics of photons transmitted by a reference system when the two systems are illuminated by a source possessing appropriate correlations. It has recently been argued that quantum entangled sources are necessary for the implementation of this technique. We show that this technique does not require entanglement, and we provide an experimental demonstration of coincidence imaging using a classical source. We further find that any kind of coincidence imaging technique which uses a "bucket" detector in the test arm is incapable of imaging phase-only objects, whether a classical or quantum source is employed.

Triple-head gamma camera PET: system overview and performance characteristics

Positron emission tomography (PET) is currently performed using either a dedicated PET scanner or scintillation gamma camera equipped with electronic circuitry for coincidence detection of 511 keV annihilation quanta (gamma camera PET system). Although the resolution limits of these two instruments are comparable, the sensitivity and count rate performance of the gamma camera PET system are several times lower than that of the PET scanner. Most gamma camera PET systems are manufactured as dual-detector systems capable of performing dual-head coincidence imaging. One possible step towards the improvement of the sensitivity of the gamma camera PET system is to add another detector head. This work investigates the characteristics of one such triple-head gamma camera PET system capable of performing triple-head coincidence imaging. The following performance characteristics of the system were assessed: spatial resolution, sensitivity, count rate performance. The spatial resolution, expressed as the full width at half-maximum (FWHM), at 1 cm radius is 5.9 mm; at 10 cm radius, the transverse radial resolution is 5.3 mm, whilst the transverse tangential and axial resolutions are 8.9 mm and 13.3 mm, respectively. The sensitivity for a standard cylindrical phantom is 255 counts.s(-1).MBq*(-1)), using a 30% width photopeak energy window. An increase of 35% in the PET sensitivity is achievable by opening an additional 30% width energy window in the Compton region. The count rate in coincidence mode, at the upper limit of the systems optimal performance, is 45 kc.s(-1) (kc=kilocounts) using the photopeak energy window only, and increases to 60 kc.s(-1) using the photopeak + Compton windows. Sensitivity results are compared with published data for a similar dual-head detector system.