Advantages Of Positron Emission Tomography Research Articles

Improved Performance of PET Myocardial Perfusion Imaging Compared to SPECT in the Evaluation of Suspected CAD.

Myocardial perfusion imaging (MPI) with single photon emission computed tomography (SPECT) has played a central role in the non-invasive evaluation of patients with obstructive coronary artery disease (CAD) for decades. In this review, we discuss the key differences and advantages of positron emission tomography (PET) MPI over SPECT MPI as it relates to the diagnosis, prognosis, as well as clinical decision-making in patients with suspected CAD. Stress-induced perfusion abnormalities on SPECT help estimate presence, extent, and location of ischemia and flow-limiting obstructive CAD, help with risk stratification, and serve as a gatekeeper to identify patients who will benefit from downstream revascularization versus medical management. Some of the major limitations of SPECT include soft-tissue attenuation artifacts, underestimation of ischemia due to reliance on relative perfusion assessment, and longer protocols with higher radiation dose when performed with traditional equipment. PET MPI addresses most of these limitations and offers better quality images, higher diagnostic accuracy along with shorter protocols and lower radiation dose to the patient. A special advantage of PET scanning lies in the ability to quantify absolute myocardial blood flow and assess true extent of epicardial involvement along with identifying non-obstructive phenotypes of CAD such as diffuse atherosclerosis and microvascular dysfunction. In addition, stress acquisition at/near peak stress with PET allows us to measure left ventricular ejection fraction reserve and myocardial blood flow reserve, which help with identifying patients at a higher risk of future cardiac events and optimally select candidates for revascularization. The several technical advantages of PET MPI position as a superior method to diagnose obstructive and non-obstructive phenotypes of ischemic heart disease affecting the entirety of the coronary circulation offer incremental value for risk stratification and guide post-test management strategy for patients with suspected CAD.

The Role of Positron Emission Tomography/ Computed Tomography (PET/CT) in Staging of Lung Cancer

Background Lung cancer is the leading cause of cancer-related death. The accurate staging of lung cancer is important in determining the optimal treatment strategy and predicting the prognosis. Positron emission tomography (PET)/computed tomography (CT), which has the advantages of PET and CT and minimizes their limitations, is a potential tool for the staging of lung cancer. Objective This study aimed to evaluate the role of PET/CT in the staging of lung cancer. Patients and methods This study was carried out on 40 patients with pathologically confirmed lung cancer referred to the Nuclear Medicine Unit affiliated to the Department of Radiodiagnosis at Sharq El Madina Hospital, Ministry of Health, Alexandria, between November 2017 and December 2019 for initial staging of lung cancer with PET/CT or restaging after therapy. Combined PET/CT imaging was performed using the Siemens biograph 64 PET/CT scanner. Results (a) Initial staging: PET/CT was able to assess the stage of ten patients (25%), whose stage could not be assessed by CECT. Both PET/CT and CECT disagreed in the staging of six patients. PET/CT staged 10 (25%) patients that could not be assessed by contrast enhanced computed tomography (CECT) and they disagreed in staging of six patients (15%). T staging was predicted by PET/CT in the 40 patients (100%) and by CECT in 30 patients (75%), with disagreement in two patients (5%). PET/CT disagreed with CECT in N staging of 10 patients (25%). PET/CT detected distant metastasis (M) in 18 patients (45%), while CECT detected it in 14 patients (35%). (b) Restaging after neoadjuvant therapy: staging was concordant in six out of eight patients (75%) and dissimilar in two patients (25%). Conclusion PET/CT is an essential component in the initial staging of lung cancer for its better locoregional and distant staging abilities. It is also more reliable in restaging after neoadjuvant therapy, being more related to the functional activity of the residual tumor rather than its size.

Benefit of [18F]-FDG PET/CT for treatment-na\xefve nasopharyngeal carcinoma

BackgroundTo test the advantages of positron emission tomography and computed tomography (PET/CT) for diagnosing lymph nodes and staging nasopharyngeal carcinoma and to investigate its benefits for survival and treatment decisions.MethodsThe performance of PET/CT and magnetic resonance imaging (MRI) in diagnosis was compared based on 460 biopsied lymph nodes. Using the propensity matching method, survival differences of T3N1M0 patients with (n = 1093) and without (n = 1377) PET/CT were compared in diverse manners. A radiologic score model was developed and tested in a subset of T3N1M0 patients.ResultsPET/CT performed better than MRI with higher sensitivity, accuracy, and area under the receiver operating characteristic curve (96.7% vs. 88.5%, p < 0.001; 88.0% vs. 81.1%, p < 0.001; 0.863 vs. 0.796, p < 0.05) in diagnosing lymph nodes. Accordingly, MRI-staged T3N0-3M0 patients showed nondifferent survival rates, as they were the same T3N1M0 if staged by PET/CT. In addition, patients staged by PET/CT and MRI showed higher survival rates than those staged by MRI alone (p < 0.05), regardless of the Epstein-Barr virus DNA load. Interestingly, SUVmax-N, nodal necrosis, and extranodal extension were highly predictive of survival. The radiologic score model based on these factors performed well in risk stratification with a C-index of 0.72. Finally, induction chemotherapy showed an added benefit (p = 0.006) for the high-risk patients selected by the model but not for those without risk stratification (p = 0.78).ConclusionPET/CT showed advantages in staging nasopharyngeal carcinoma due to a more accurate diagnosis of lymph nodes and this contributed to a survival benefit. PET/CT combined with MRI provided prognostic factors that could identify high-risk patients and guide individualized treatment.

In Vivo Imaging of Folate Receptor Positive Tumor Xenografts Using Novel 68Ga-NODAGA-Folate Conjugates

The overexpression of the folate receptor (FR) in a variety of malignant tumors, along with its limited expression in healthy tissues, makes it an attractive tumor-specific molecular target. Noninvasive imaging of FR using radiolabeled folate derivatives is therefore highly desirable. Given the advantages of positron emission tomography (PET) and the convenience of (68)Ga production, the aim of our study was to develop a new (68)Ga-folate-based radiotracer for clinical application. The chelator 1,4,7-triazacyclononane,1-glutaric acid-4,7-acetic acid (NODAGA) was conjugated to folic acid and to 5,8-dideazafolic acid using 1,2-diaminoethane as a spacer, resulting in two novel conjugates, namely, P3246 and P3238, respectively. Both conjugates were labeled with (68/67)Ga. In vitro internalization, efflux, and saturation binding studies were performed using the FR-positive KB cell line. Biodistribution and small-animal PET imaging studies were performed in nude mice bearing subcutaneous KB xenografts. Both conjugates were labeled with (68)Ga at room temperature within 10 min in labeling yields >95% and specific activity ~30 GBq/μmol. The K(d) values of (68/67)Ga-P3246 (5.61 ± 0.96 nM) and (68/67)Ga-P3238 (7.21 ± 2.46 nM) showed high affinity for the FR. (68/67)Ga-P3246 showed higher cell-associated uptake in vitro than (68/67)Ga-P3238 (approximately 72 and 60% at 4 h, respectively, P < 0.01), while both radiotracers exhibited similar cellular retention up to 4 h (approximately 76 and 71%, respectively). Their biodistribution profile is characterized by high tumor uptake, fast blood clearance, low hepatobiliary excretion, and almost negligible background. Tumor uptake was already high at 1 h for both (68)Ga-P3246 and (68)Ga-P3238 (16.56 ± 3.67 and 10.95 ± 2.12% IA/g, respectively, P > 0.05) and remained at about the same level up to 4 h. Radioactivity also accumulated in the FR-positive organs, such as kidneys (91.52 ± 21.05 and 62.26 ± 14.32% IA/g, respectively, 1 h pi) and salivary glands (9.05 ± 2.03 and 10.39 ± 1.19% IA/g, respectively, 1 h pi). The specificity of the radiotracers for the FR was confirmed by blocking experiments where tumor uptake was reduced by more than 85%, while the uptake in the kidneys and the salivary glands was reduced by more than 90%. Reduction of the kidney uptake was achieved by administration of the antifolate pemetrexed 1 h prior to the injection of the radiotracers, which resulted in an improvement of tumor-to-kidney ratios by more than a factor of 3. In line with the biodistribution results, small-animal PET images showed high uptake in the kidneys, clear visualization of the tumor, accumulation of radioactivity in the salivary glands, and no uptake in the gastrointestinal tract. (68)Ga-P3246 and (68)Ga-P3238 showed very high tumor-to-background contrast in PET images; however, the tumor-to-kidney ratio remained low. The new radiotracers, especially (68)Ga-P3246, are promising as PET imaging probes for clinical application due to their facile preparation and improved in vivo profile as compared to the other folate-based PET radiotracers.

PET without cyclotron

Positron emission tomography (PET) has been well established noninvasive imaging technique for diagnosis, staging/ restaging and monitoring of therapy response in oncology. Molecular imaging using positron emitting radionuclides kinetics provides quantitative in vivo assessment of biological and physiological processes involved in the earlier stages of disease progression. Because of the short life time (hours) of many of the PET radioisotopes, a cyclotron and radiocompound synthesis facility is required. One of the most widely recognized advantages of PET is the use of the positron emitting biologic radiotracers, e.g., C (T = 20 min), N (T = 10 min), O (T = 2 min), and most important F (T = 110 min) that mimic natural substrate. However, due to relatively short half-lives, they are unable to be transported to sites at great distances from the production facility. The production of radioisotopes using a cyclotron/accelerator demands a knowledge of excitation functions (reaction cross section), development of high current targets, radiochemical separations at no-carrier added level, recovery of enriched target materials in most of the cases, remote control and highly trained manpower for running, repair and maintenance. Cyclotrons are generally used for production of short-lived radioisotopes; however, long-lived isotopes are also produced which can be used at distant places. Fast and high resolution imaging method, such as single photon emission computed tomography (SPECT) is now commonly available for diagnostic studies in developing countries, whereas PET facility is rarely employed for patient management due to non-availability of cyclotron in these countries. Positron emission tomography has two major advantages over SPECT, namely, better spatial resolution and greater sensitivity. The number of positron emitting radionuclides is large. However, most of the PET studies are performed near to cyclotron production facility with short-lived positron emitters (C, O, N, and F). A tabulation of 157 positron emitting radionuclides which have the physical characteristics deemed appropriate for radiopharmaceutical use is provided by Lambrecht [1]. Some cyclotron produced generator radionuclides have also been listed by Qaim [2]. Table 1 presents the generator produced positron emitters, which can be utilized far from production site for PET studies. Production route of parent in a cyclotron and separation of daughter is discussed elsewhere [3]. Antibody-PET imaging might be of value for the selection of radioimmunotherapy (RIT) candidates to confirm tumor targeting and to estimate radiation doses to tumor and normal tissues. One of the requirements to be set for such a scouting procedure is that the biodistributions of the diagnostic and therapeutic radioimmunoconjugates should be similar. The potential of the positron emitters zirconium-89 (Zr) and iodine-124 (I) for this approach, as these radionuclides have a relatively long half-life that matches with the kinetics of MAbs in vivo (T1/2 3.27 and 4.18 days, respectively), were evaluated [4]. Other long-lived positron emitters, which may be used at distant places are, V (T = 16 d), Mn (T = 5.59 days), As (T = 17.78 days), and Au (T = 39.5 h). Through the supply of a long-lived parent radionuclide, from which a short-lived daughter radionuclide can be milked off periodically at hospitals, it has become possible A. Mushtaq (&) Isotope Production Division, Pakistan Institute of Nuclear Science and Technology, P.O. Nilore, Islamabad, Pakistan e-mail: mushtaqa@pinstech.org.pk

Is PET always an advantage versus planar and SPECT imaging?

The article by Abass Alavi and Sandip Basu in this issue of the European Journal of Nuclear Medicine and Molecular Imaging vividly embodies, in a scenario that seems to be easy to reach, the expectations that imaging through positron emission tomography (PET) has raised in the nuclear medicine community at large. In Alavi’s view, this scenario resolutely points to soon-to-come wide availability of a complete armamentarium of PET radiopharmaceuticals capable of substituting virtually all of the single photon agents currently employed. Therefore, the most likely horizon that the author depicts for the future of diagnostic nuclear medicine is PET imaging, with dismal chances for both planar imaging and single photon computed tomography (SPECT) to even survive in the daily clinical routine [1]. For envisaging the inescapable evolution from single photon to PET imaging, Alavi presents an exciting compendium of the many routes followed to achieve the long-pursued “dream come true” for nuclear medicine, i.e., functional imaging combined with the highest possible anatomic definition, thus directly translating molecular/ metabolic information into an immediate clinical impact for the widest possibile range of disease states. Two examples are especially poignant to illustrate Alavi’s view on what he considers to be an irreversibile trend for nuclear medicine imaging: (1) agents other than F-fluoro-deoxy-glucose ([F]FDG) based on fluorine-18, and (2) peptides labeled with gallium-68. To the former group belong F-fluoride for exploring bone turnover in place of bone scintigraphy with Tc-phosphonates (possibly the diagnostic procedure most commonly performed in clinical nuclear medicine) and F-Fluoro-DOPA for exploring neuroendocrine tumors [2]. To Alavi’s list we would also add PET with F-Fluoro-DOPA [3, 4] in place of SPECT with either I-FP-CIT or Tc-Trodat-1 for investigating movement disorders (one of the fastest growing applications in conventional nuclear medicine imaging). The advantages of PET with Ga-labeled somatostatin analogs over SPECT with In-peptides for localizing neuroendocrine tumors are also obvious [5], considering the possibility of supplying nuclear medicine centers with Ge/Ga generators at a relatively low cost. Nevertheless, although we certainly share many of the issues and expectations raised by Alavi in support of his view on the future prospects of radionuclide imaging, we do not totally share his optimistic view on the soon-to-come large-scale availability of several PET radiopharmaceuticals and his conclusion on the impending obsolescence of single photon planar and tomographic imaging. Our position is based on several considerations dealing with a wide range of issues including physical quality of the emissions of radionuclides, continuing clinical impact of imaging that can only be based on single-photon emission, regulation of approval for new agents, and finally local socioeconomic factors worldwide. Eur J Nucl Med Mol Imaging (2008) 35:1560–1565 DOI 10.1007/s00259-008-0814-1

Characteristics of Advantages of Positron Emission Tomography over Computed Tomography for N-staging in Lung Cancer Patients

We analyzed the characteristics of advantages of positron emission tomography (PET) over computed tomography (CT) for N-staging in lung cancer patients. Preoperative PET and CT scans were performed for 2057 lymph node stations in 205 patients with peripheral-type lung cancer. The advantages of PET over CT for N-staging were analyzed among lymph node locations and histological subtypes. The pathological N-stages were N0 in 143 patients, N1 in 31, N2 in 24 and N3 in 7. PET was able to diagnose N0, N2 and N3 diseases more accurately than CT (P=0.03, 0.01 and 0.02, respectively), but there was no significant difference between the two modalities for N1 disease. In the upper mediastinal lymph node stations, both false-negative and false-positive were significantly less frequent with PET than with CT (P=0.001). In the lower mediastinal and supra clavicle lymph nodes, PET showed a lower frequency of false-negative than CT (P=0.04 and 0.003, respectively), but there was no significant difference in the frequency of false-positive between the two modalities. Among histological types, PET could stage adenocarcinoma with less frequent false-negative and squamous cell carcinoma with less frequent false-positive than CT (P=0.02 and 0.005, respectively). For N-staging, PET was superior to CT for the following: (1) more accurate for N0, N2 and N3 diseases but not for N1; (2) lower frequency of false-positive in the upper mediastinal nodes; and (3) lower frequencies of false-negative in adenocarcinoma and false-positive in squamous cell carcinoma. Recognizing these advantages of PET could make the N-staging of lung cancer more accurate.

Positron Emission Tomography: A Promising Diagnostic Modality for Head and Neck Pathology

The purpose of this study is to discuss the advantages of positron emission tomography (PET) imaging in the diagnosis of head and neck lesions. To illustrate this diagnostic method, we describe the nuclear medicine basic technique, present 5 cases for comparison of the results between computed tomography (CT) scan and PET, and review the literature. The 5 cases show that PET allows assessment of lesions earlier and more definitively than other diagnostic images. PET, a nuclear medicine modality, is a promising tool for diagnosis and follow-up of head and neck lesions. PET allows assessment of changes in the tissue before they would be shown by other diagnostic images. This modality permits differentiation between malignant and benign tumors. It also has the capability to distinguish between scar tissue, necrosis, tumor recurrence, and metastatic disease. It allows the assessment of the patient's progress during therapy, making possible an early identification of nonresponders to therapy.

Application of PET/CT in children

Positron Emission Tomography (PET) can dynamically image trace amounts of radiopharmaceuticals in vivo. By applying appropriate tracer kinetic models, tracer concentrations can be determined quantitatively. In addition to superior spatial resolution and quantitative potential, PET also offers much greater sensitivity (i.e., number of y-rays detected per unit injected dose) than single photon emission computed tomography (SPECT). Furthermore, the biologic ubiquity of the elements that are positron emitters gives PET unprecedented power to image the distribution and kinetics of natural and analog biologic tracers. Because of the exquisite sensitivity of detection systems to y-ray emission, these biologic probes can be introduced in trace amounts (nanoor even picomolar concentrations) that do not disturb the biologic process under investigation. By combining a tracer that is selective for a specific biochemical pathway, an accurate tracer kinetic model, and a dynamic sequence of quantitative images from the PET scanner, it is possible to estimate the absolute rates of biologic processes in that pathway. Examples of such processes that have been successfully measured with PET include regional cerebral and myocardial blood flow, rates of glucose utilization, rates of protein synthesis, cerebral and myocardial oxygen consumption, synthesis of neurotransmitters, enzyme assays, and receptor assays. In summary, some of the distinctive advantages of PET are its exquisite sensitivity, the flexible chemistry, and the better imaging characteristics of PET isotopes. Thus PET provides access to biological processes that is well beyond the scope of current MR technology. The radioactive decay of many radioisotopes generates penetrating photons capable of escaping outside the matter in which the isotopes are located. From this radiation it is possible to image the spatial distribution of such isotopes inside an object. When imaging humans, it is necessary to use photons capable of escaping undeflected from a few

Advantages of Positron Emission Tomography over Computed Tomography in Mediastinal Staging of Non-Small Cell Lung Cancer

Background. New treatment algorithms in early stage non-small cell lung cancer (NSCLC) involving preoperative chemotherapy require accurate clinical staging of the mediastinum. This study compares the accuracy of 2-[fluorine-18]fluoro-2-deoxy-d-glucose (FDG) positron emission tomography (PET) scanning with that of computed tomography (CT) scanning in the clinical staging of non-small cell lung cancer.Materials and methods. A retrospective review was performed on 52 patients with NSCLC who were evaluated with both CT and PET scans. All patients had their mediastinal lymph nodes sampled by mediastinoscopy or at the time of thoracotomy for pulmonary resection. Each imaging study was evaluated separately and correlated with histopathologic results.Results. For detecting mediastinal metastases the sensitivities of PET and CT scans were 67 and 50%, respectively; specificities were 91 and 65%, respectively; accuracies were 88 and 63%, respectively; positive predictive values were 50 and 16%, respectively; negative predictive values were 95 and 88%, respectively. PET scans were significantly better than CT scans at detecting mediastinal metastases (PET, 4/8; CT, 3/19) (P = 0.01).Conclusions. PET scanning is superior to CT scanning for clinical staging of the mediastinum in NSCLC. A more confident decision regarding stratification of patients into current treatment algorithms can be made when the decision is based on PET scanning rather than the current “gold standard” of CT scanning.

Advantages of Positron Emission Tomography (PET) with Respect to Computed Tomography in the Follow-up of Lymphoma Patients with Abdominal Presentation

For abdominal lymphoma patients, fluorine-18 fluorodeoxyglucose positron emission tomography (PET) provides unique information on the presence of residual active disease. We provide an update on the largest reported cohort of patients whose management following induction therapy was based on routine PET and computed tomography (CT) restaging. Fifty-nine patients with Hodgkin's disease or aggressive non-Hodgkin's lymphoma presenting abdominal involvement (35% with bulky disease) were studied with both PET and CT following combined chemotherapy/radiation treatment. After treatment, 3/3 (100%) patients who were PET+/CT- relapsed, compared with 0/7 patients in the PET-/CT- subset. Among the 49 patients who were CT+, six of the 10 (60%) who were PET+ relapsed, as compared with only two of the 39 (5%) who were PET-. The actuarial relapse-free survival (RFS) rates were 0 and 100% in the PET+/CT- and PET-/CT- subsets, respectively. In the PET+/CT+ subset, RFS was 94% at 5 years. PET restaging is very valuable for the identification of patients who would need appropriate second-line therapy because of the presence of residual active abdominal disease and should be made widely available in combination with CT.

The search for consistency in the manufacture of PET radiopharmaceuticals.

Nuclear Medicine is the specialty of medical imaging, which utilizes a variety of radionuclides incorporated into specific compounds for diagnostic imaging and therapeutic applications. During recent years, research efforts in this discipline have concentrated on the decay characteristics of particular radionuclides and the design of unique radiolabeled tracers necessary to achieve time-dependent molecular images. Various oncology applications have utilized specific PET and SPECT radiopharmaceuticals, which have allowed an extension from functional process imaging in tissue to pathologic processes and nuclide directed treatments. One of the most widely recognized advantages of positron emission tomography (PET) is its use of the attractive, positron-emitting biologic radiotracers that mimic natural substrates. However, a major disadvantage is that these substances are relatively short-lived and unable to be transported great distances. At this time, economic considerations and regulatory guidelines associated with the creation of a PET facility, as well as the operational costs of maintaining both the facility and the necessary procedural documentation, continue to create interesting strategic dilemmas. This commentary will focus on the current approach and anticipated impact of pending regulations, which relate to the manufacture and formulation of a variety of PET radiopharmaceuticals used in clinical research and patient management at Memorial Hospital.

Positron emission tomography in oncology.

The particular advantages of positron emission tomography (PET) technique are that it has higher sensitivity, higher resolution, and a higher quality of image than that found in conventional nuclear medicine. The possibility of quantification and the wide range of useful tracers have raised expectations of this new method. To date, most of the human PET cancer studies have been performed with [18F]fluorodeoxyglucose (FDG) or [11C]methionine. These are good imaging agents for tumours. However, more specific radiopharmaceuticals are required if other features of tumour metabolism are to be observed. [11C]Thymidine may prove to be a good tracer for quantitative measurements of tumour proliferation and [18F]misonidazole has been suggested for imaging of hypoxia.