Anatomical Imaging Techniques Research Articles

Prostate Cancer: Multiparametric MR Imaging for Detection, Localization, and Staging

This review presents the current state of the art regarding multiparametric magnetic resonance (MR) imaging of prostate cancer. Technical requirements and clinical indications for the use of multiparametric MR imaging in detection, localization, characterization, staging, biopsy guidance, and active surveillance of prostate cancer are discussed. Although reported accuracies of the separate and combined multiparametric MR imaging techniques vary for diverse clinical prostate cancer indications, multiparametric MR imaging of the prostate has shown promising results and may be of additional value in prostate cancer localization and local staging. Consensus on which technical approaches (field strengths, sequences, use of an endorectal coil) and combination of multiparametric MR imaging techniques should be used for specific clinical indications remains a challenge. Because guidelines are currently lacking, suggestions for a general minimal protocol for multiparametric MR imaging of the prostate based on the literature and the authors' experience are presented. Computer programs that allow evaluation of the various components of a multiparametric MR imaging examination in one view should be developed. In this way, an integrated interpretation of anatomic and functional MR imaging techniques in a multiparametric MR imaging examination is possible. Education and experience of specialist radiologists are essential for correct interpretation of multiparametric prostate MR imaging findings. Supportive techniques, such as computer-aided diagnosis are needed to obtain a fast, cost-effective, easy, and more reproducible prostate cancer diagnosis out of more and more complex multiparametric MR imaging data.

Newer CT applications and their alternatives: what is appropriate in children?

Innovations in image acquisition and reconstruction technologies have greatly expanded the range of CT applications available in the routine clinical setting. CT images of sub-millimeter resolution can now be acquired of entire body regions in a few seconds or even sub-second time, allowing depiction of fine anatomical detail uncompromised by motion artifact. With sophisticated visualization software, image data can be processed into multiplanar, volume-rendered, cine and other formats to better display anatomical abnormalities and facilitate newer applications such as CT angiography, enterography, urography, tracheobronchography and cardiac CT. Newer applications including dual-energy material decomposition CT are furthering the transition of CT from a purely morphological to a combined anatomical, functional and metabolic imaging technique. These newer applications have largely been pioneered in adult populations, and heightened concern of the risk of carcinogenesis from ionizing radiation tempers dissemination of their use in children. Similar information can often be gleaned from alternative imaging modalities without ionizing radiation exposure, such as MRI and US, and what is most appropriate in children will depend on relative diagnostic efficacy, cost, availability and local expertise.

Imaging Studies in Hypercalcemia

Hypercalcemia is a relatively common clinical problem, mainly (>90%) related to primary hyperparathyroidism (HPT) and malignancies. The anatomical and functional imaging techniques available for locating enlarged parathyroid glands include ultrasound (US), computed tomography (CT), magnetic resonance imaging (MRI), and nuclear medicine imaging techniques. The most commonly employed are US and parathyroid scintigraphy, while CT, MRI, positron emission tomography (PET)/CT, and selective venous sampling are generally used in patients with persistent or recurrent HPT, or when findings of non-invasive studies are negative or conflicting. The reported accuracy is 57-93%, 54-93%, and up to 95% for US, (99m)Tc-sestamibi scintigraphy, and the two modalities combined, respectively. A multimodality approach (x-ray, whole-body scintigraphy, CT, MRI, and PET) is usually recommended for whole body assessment in cases of cancer-induced hypercalcemia (CIH). Imaging studies should evaluate each organ (i.e. breast, kidney, prostate, parathyroid) potentially involved in the pathogenesis of hypercalcemia in patients with CIH. In cases of skeletal metastases, when findings on plain x-ray or bone scans are uncertain, any unexplained region of abnormal uptake should be examined by MRI and/or ¹⁸F-fluoro-2- deoxyglucose (FDG)-PET/CT, which has proved more accurate than classical bone scintigraphy, especially for dealing with hematologic malignancies. A number of radionuclide tracers, other than ¹⁸F-FDG, are available for use in selected cases to locate specific tumors (i.e. ⁶⁸Ga for neuroendocrine tumors). This is a review of recently published information on the imaging techniques currently available for patients with hypercalcemia.

Functional Imaging ofSDHx-Related Head and Neck Paragangliomas: Comparison of18F-Fluorodihydroxyphenylalanine,18F-Fluorodopamine,18F-Fluoro-2-Deoxy-d-Glucose PET,123I-Metaiodobenzylguanidine Scintigraphy, and111In-Pentetreotide Scintigraphy

Accurate diagnosis of head and neck paragangliomas is often complicated by biochemical silence and lack of catecholamine-associated symptoms, making accurate anatomical and functional imaging techniques essential to the diagnostic process. Ten patients (seven SDHD, three SDHB), with a total of 26 head and neck paragangliomas, were evaluated with anatomical and functional imaging. This study compares five different functional imaging techniques [(18)F-fluorodihydroxyphenylalanine ((18)F-FDOPA) positron emission tomography (PET), (18)F-fluorodopamine ((18)F-FDA) PET/computed tomography (CT), (18)F-fluoro-2-deoxy-D-glucose ((18)F-FDG) PET/CT, (123)I-metaiodobenzylguanidine ((123)I-MIBG) scintigraphy, and (111)In-pentetreotide scintigraphy] in the localization of head and neck paragangliomas. Prospectively (18)F-FDOPA PET localized 26 of 26 lesions in the 10 patients, CT/magnetic resonance imaging localized 21 of 26 lesions, (18)F-FDG PET/CT localized 20 of 26 lesions, (111)In-pentetreotide scintigraphy localized 16 of 25 lesions, (18)F-FDA PET/CT localized 12 of 26 lesions, and (123)I-MIBG scintigraphy localized eight of 26 lesions. Differences in imaging efficacy related to genetic phenotype, even in the present small sample size, included the negativity of (18)F-FDA PET/CT and (123)I-MIBG scintigraphy in patients with SDHB mutations and the accuracy of (18)F-FDG PET/CT in all patients with SDHD mutations, as compared with the accuracy of (18)F-FDG PET/CT in only one patient with an SDHB mutation. Overall, (18)F-FDOPA PET proved to be the most efficacious functional imaging modality in the localization of SDHx-related head and neck paragangliomas and may be a potential first-line functional imaging agent for the localization of these tumors.

Advances in imaging in differentiated thyroid cancer: focus on SPECT/CT and PET/CT

Thyroid cancer is the most common cancer of the endocrine system and has exhibited a steady rise in incidence over the last 30 years. The management of thyroid cancer requires a multidisciplinary approach and imaging is important for diagnosis, staging, surveillance and risk stratification. Anatomical imaging techniques, such as ultrasound, computed tomography (CT) and MRI, are used for the detection and characterization of thyroid nodules, assessment of nodal disease and to evaluate for extrathyroidal spread of disease prior to surgery. Functional imaging using 123I and 131I studies provide important prognostic information, confirm radioiodine avidity of tumor in preparation for 131I therapy and detect metastatic disease, thereby directing further management. Hybrid imaging combines the individual strengths of the anatomical and functional imaging modalities, providing the clinician with a powerful management tool. In this article, we look at the role of imaging, with a particular focus on the emerging role of hybrid imaging modalities, such as single photon emission computed tomography/CT and positron emission tomography/CT, in the management of differentiated thyroid cancer.

Validation of Imaging With Pathology in Laryngeal Cancer: Accuracy of the Registration Methodology

To investigate the feasibility and accuracy of an automated method to validate gross tumor volume (GTV) delineations with pathology in laryngeal and hypopharyngeal cancer. High-resolution computed tomography (CT(HR)), magnetic resonance imaging (MRI), and positron emission tomography (PET) scans were obtained from 10 patients before total laryngectomy. The GTV was delineated separately in each imaging modality. The laryngectomy specimen was sliced transversely in 3-mm-thick slices, and whole-mount hematoxylin-eosin stained (H&E) sections were obtained. A pathologist delineated tumor tissue in the H&E sections (GTV(PATH)). An automatic three-dimensional (3D) reconstruction of the specimen was performed, and the CT(HR), MRI, and PET were semiautomatically and rigidly registered to the 3D specimen. The accuracy of the pathology-imaging registration and the specimen deformation and shrinkage were assessed. The tumor delineation inaccuracies were compared with the registration errors. Good agreement was observed between anatomical landmarks in the 3D specimen and in the invivo images. Limited deformations and shrinkage (3% ± 1%) were found inside the cartilage skeleton. The root mean squared error of the registration between the 3D specimen and the CT, MRI, and PET was on average 1.5, 3.0, and 3.3 mm, respectively, in the cartilage skeleton. The GTV(PATH) volume was 7.2 mL, on average. The GTVs based on CT, MRI, and PET generated a mean volume of 14.9, 18.3, and 9.8 mL and covered the GTV(PATH) by 85%, 88%, and 77%, respectively. The tumor delineation inaccuracies exceeded the registration error in all the imaging modalities. Validation of GTV delineations with pathology is feasible with an average overall accuracy below 3.5 mm inside the laryngeal skeleton. The tumor delineation inaccuracies were larger than the registration error. Therefore, an accurate histological validation of anatomical and functional imaging techniques for GTV delineation is possible in laryngeal cancer patients.

Pediatric oncology and the future of oncological imaging

The future of pediatric oncology will be influenced by changes in drug design and treatment strategy, with genomic medicine and molecular-based diagnostics and therapeutics playing increasingly important roles. The role of imaging as a means of measuring response to therapy has also evolved, with the development of new technologies and higher sensitivity means of detecting tumors. Conventional anatomical imaging techniques are being increasingly supplemented with functional techniques, including FDG-PET imaging and diffusion-weighted MR imaging. The risk-adapted treatment regimens of the past, which led to improved event-free and overall survival in many pediatric cancers, have paved the way for new response-based treatment paradigms. Response-based approaches seek to identify patients with a high likelihood of cure, treating them less aggressively, while those not responding to therapy are identified early and redirected into more aggressive therapeutic regimens. These advances will require concurrent development of imaging biomarkers as surrogates of early response to therapy. Incorporating these techniques into new response-directed treatment algorithms will be crucial as personalized medicine and molecular-targeted, tumor-specific therapies gain acceptance for the treatment of children with cancer.

Imaging of osteomyelitis: the key is in the combination

An accurate diagnosis of osteomyelitis requires the combination of anatomical and functional imaging techniques. Conventional radiography is the first imaging modality to begin with, as it provides an overview of both the anatomy and the pathologic conditions of the bone. Sonography is most useful in the diagnosis of fluid collections, periosteal involvement and soft tissue abnormalities, and may provide guidance for diagnostic or therapeutic interventions. MRI highlights sites with tissue edema and increased regional perfusion, and provides accurate information of the extent of the infectious process and the tissues involved. To detect osteomyelitis before anatomical changes are present, functional imaging could have some advantages over anatomical imaging. Fluorine-18 fluorodeoxyglucose-PET has the highest diagnostic accuracy for confirming or excluding the diagnosis of chronic osteomyelitis. For both SPECT and PET, specificity improves considerably when the scintigraphic images are fused with computed ...

Clinical applications of positron emission tomography in sarcoma management

Positron emission tomography (PET) with the fluorine-18-labeled glucose analog FDG is a technique that noninvasively visualizes glucose metabolism in the human body. In oncology, the addition of FDG-PET to the conventional anatomical imaging techniques provides very useful clinical information in diagnosis, staging, treatment response monitoring and follow-up. In the heterogeneous group of patients with sarcoma, FDG-PET has been shown to be of great value in improving patient care. In this article we will discuss the current role of FDG-PET in the management of patients with sarcoma and its value in assessing tumor grade, guiding biopsy, staging, monitoring treatment response, restaging and prognostication. Our future expectation is that the value of PET will only augment owing to the implementation of FDG-PET in clinical guidelines, the increasing availability worldwide, and the development of new tracers and new hybrid imaging techniques.

MRI of the prostate: Clinical relevance and emerging applications

MRI of the prostate can aid in many aspects of prostate cancer management, from initial detection to treatment planning and follow-up. This review describes the current strengths and limitations of conventional anatomic and molecular MR imaging techniques (including MR spectroscopic imaging and dynamic contrast-enhanced imaging) for aiding prostate cancer management. It also describes promising emerging approaches for acquiring, analyzing, and applying MR imaging data, and the major research and educational efforts that will be required to realize the potential of prostate MR imaging in routine clinical practice.

The Non-Random Brain: Efficiency, Economy, and Complex Dynamics

Modern anatomical tracing and imaging techniques are beginning to reveal the structural anatomy of neural circuits at small and large scales in unprecedented detail. When examined with analytic tools from graph theory and network science, neural connectivity exhibits highly non-random features, including high clustering and short path length, as well as modules and highly central hub nodes. These characteristic topological features of neural connections shape non-random dynamic interactions that occur during spontaneous activity or in response to external stimulation. Disturbances of connectivity and thus of neural dynamics are thought to underlie a number of disease states of the brain, and some evidence suggests that degraded functional performance of brain networks may be the outcome of a process of randomization affecting their nodes and edges. This article provides a survey of the non-random structure of neural connectivity, primarily at the large scale of regions and pathways in the mammalian cerebral cortex. In addition, we will discuss how non-random connections can give rise to differentiated and complex patterns of dynamics and information flow. Finally, we will explore the idea that at least some disorders of the nervous system are associated with increased randomness of neural connections.

Role of 18F-fluoro-2-deoxyglucose Positron Emission Tomography in Gastric GIST: Predicting Malignant Potential Pre-operatively

PurposeIt is difficult to obtain biopsies from gastrointestinal stromal tumors (GISTs) prior to surgery because GISTs are submucoal tumors, despite being the most common nonepithelial neoplasms of the gastrointestinal tract. Unlike anatomic imaging techniques, PET-CT, which is a molecular imaging tool, can be a useful technique for assessing tumor activity and predicting the malignant potential of certain tumors. Thus, we aimed to evaluate the usefulness of PET-CT as a pre-operative prognostic factor for GISTs by analyzing the correlation between the existing post-operative prognostic factors and the maximum SUV uptake (SUVmax) of pre-operative 18F-fluoro-2-deoxyglucose (FDG) PET-CT.Materials and MethodsThe study was conducted on 26 patients who were diagnosed with gastric GISTs and underwent surgery after being examined with pre-operative FDG PET-CT. An analysis of the correlation bewteen (i) NIH risk classfication and the Ki-67 proliferation index, which are post-operative prognostic factors, and (ii) the SUVmax of PET-CT, which is a pre-operative prognostic factor, was performed.ResultsThere were significant correlations between (i) SUVmax and (ii) Ki-67 index, tumor size, mitotic count, and NIH risk group (r=0.854, 0.888, 0.791, and 0.756, respectively). The optimal cut-off value for SUVmax was 3.94 between "low-risk malignancy" and "high-risk malignancy" groups. The sensitivity and specificity of SUVmax for predicting the risk of malignancy were 85.7% and 94.7%, respectively.ConclusionsThe SUVmax of PET-CT is associated with Ki-67 index, tumor size, mitotic count, and NIH classification. Therefore, it is believed that PET-CT is a relatively safe, non-invasive diagnostic tool for assessing malignant potential pre-operatively.

Pathways of Lymphatic Spread in Male Urogenital Pelvic Malignancies

Regional lymph node involvement in urogenital malignancies (category N in the TNM classification system) is a significant radiologic finding, with important implications for treatment and prognosis. Male urogenital pelvic cancers commonly spread to iliopelvic or retroperitoneal lymph nodes by following pathways of normal lymphatic drainage from the pelvic organs. The most likely pathway of nodal spread (superficial inguinal, pelvic, or paraaortic) depends on the tumor location in the prostate, penis, testis, or bladder and whether surgery or other therapy has disrupted normal lymphatic drainage from the tumor site; knowledge of both factors is needed for accurate disease staging. At present, lymph node status is most often assessed with standard anatomic imaging techniques such as multidetector computed tomography or magnetic resonance (MR) imaging. However, the detection of nodal disease with these techniques is reliant on lymph node size and morphologic characteristics, criteria that provide limited diagnostic specificity. Functional imaging techniques, such as diffusion-weighted MR imaging performed with or without a lymphotropic contrast agent and positron emission tomography, may allow a more accurate nodal assessment based on molecular or physiologic activity.

Imaging of Abdominal Aortic Aneurysm: The Present and the Future

Abdominal Aortic Aneurysm (AAA) is a common, progressive, and potentially lethal vascular disease. A major obstacle in AAA research, as well as patient care, is the lack of technology that enables non-invasive acquisition of molecular/cellular information in the developing AAA. In this review we will briefly summarize the current techniques (e.g. ultrasound, computed tomography, and magnetic resonance imaging) for anatomical imaging of AAA. We also discuss the various functional imaging techniques that have been explored for AAA imaging. In many cases, these anatomical and functional imaging techniques are not sufficient for providing surgeons/clinicians enough information about each individual AAA (e.g. rupture risk) to optimize patient management. Recently, molecular imaging techniques (e.g. optical and radionuclide-based) have been employed to visualize the molecular alterations associated with AAA, which are discussed in this review. Lastly, we try to provide a glance into the future and point out the challenges for AAA imaging. We believe that the future of AAA imaging lies in the combination of anatomical and molecular imaging techniques, which are largely complementary rather than competitive. Ultimately, with the right molecular imaging probe, clinicians will be able to monitor AAA growth and evaluate the risk of rupture accurately, so that the life-saving surgery can be provided to the right patients at the right time. Equally important, the right imaging probe will also allow scientists/clinicians to acquire critical data during AAA development and to more accurately evaluate the efficacy of potential treatments.

Molekulare Bildgebung in der Tumortherapie

Targeted drugs that modulate the function of specific molecules in diseased tissues hold great promise for the treatment of many diseases, including malignant tumors. However, there are several challenges for the efficient evaluation of these drugs in clinical trials as well as for the use in clinical practice. These include (i) the selection of patients likely to benefit from treatment with a specific targeted drug, (ii) finding the right dose and dose schedule, (iii) monitoring target inhibition, and (iv) assessing tumor response to therapy. Standard anatomic imaging continues to play an important role for addressing these challenges, but molecular imaging provides several new opportunities to make the use of targeted drugs more efficient. Using molecular imaging, the expression of drug targets can be assessed noninvasively, the concentration of drugs can be measured in the tumor tissue, target inhibition can be monitored, and tumor response to therapy can be evaluated earlier than with anatomic imaging techniques. Therefore, it is expected that molecular imaging will play an increasing role for guiding molecularly defined therapeutic interventions.

Functional Magnetic Resonance Imaging of Mild Traumatic Brain Injury

Mild traumatic brain injury (MTBI) is a serious health problem that has been difficult to study because of the relative insensitivity of established anatomical imaging techniques for detecting the associated neural damage and dysfunction. Functional magnetic resonance imaging (fMRI) offers potential for understanding the neural and functional basis of MTBI and the relationship to behavioral and somatic symptoms. This article reviews the recent fMRI literature relevant to the study of MTBI. The pathophysiology of MTBI and the neural basis of the blood oxygen level-dependent fMRI response are also considered with particular focus on important issues for using fMRI to investigate MTBI.

Functional imaging of the pediatric brain and new technics

Most disorders affecting the pediatric brain are discovered because of functional deficits. Until recently most functional deficits were approached by anatomical imaging techniques rather than by functional techniques. This is even more striking taking into accounts that treatment options should preferably restore or optimize brain function rather than brain anatomy. Frequently the anatomical lesions are only the tip of the iceberg. Early, sensitive and specific identification of pathology is even more important in the pediatric population because functional brain plasticity is more outspoken in children compared to adults. Moreover, a functional deficit may interfere with or prevent normal development of the pediatric brain. Currently, many functional MRI techniques are being developed and give complementary information to anatomical MRI techniques. In the current review we will discuss different MRI applications that can be routinely applied in pediatric neuroradiology that render different functional information including multitensor diffusion tensor imaging, perfusion weighted imaging, 1H and 31P magnetic resonance spectroscopy, pH-weighted MRI, and susceptibility weighted MRI. We will discuss in particular how these different functional approaches serve as complementary techniques in solving the mystery of pediatric neurological diseases.

Accurate 3D Registration of Pathology with Imaging for Target Delineation in Laryngeal Cancer Patients

Pathology is the gold standard to define the gross target volume (GTV) and the clinical target volume (CTV) in radiotherapy. The purpose of this study is to investigate the feasibility and estimate the accuracy of a 3D reconstruction of histopathology and of its registration with pretreatment imaging, in laryngeal cancer. High resolution CT, dynamic contrast enhanced CT, FDG-PET, and MRI (T1w, T2w, GdT1w and diffusion weighted) scans were obtained before total laryngectomy (TLE) from 6 patients positioned using the radiotherapy mask. After fixation of the TLE specimen with formalin, three carbon rods were introduced as an internal reference. To avoid deformations during slicing, the specimen was evolved in a block of Agar, on which also carbon rods were introduced. The specimen in the block was sliced transversally in 3 mm thick sections, which were photographed from both the caudal and cranial side. Subsequently, hematoxylin-eosin (H&E) sections were obtained. The carbon rods in the Agar, as well as anatomical cartilage landmarks were used to reconstruct the specimen using a manual point-based rigid registration. The contrast of the cartilage was manually enhanced, allowing a rigid registration using mutual information (MI) between the 3D specimen and the CT. Rigid registration using MI was applied to register the CT with the images of the other modalities. The H&E sections were manually registered to the 3D specimen using the carbon rods and anatomical landmarks in the cartilage. Using in-house developed software all registered images were viewed simultaneously and excellent agreement was observed between anatomical landmarks in the 3D specimen and those in the in-vivo images. The accuracy of the reconstruction of the specimen was assessed to be within 1 mm. The registration error in the transversal plane was, on average, 1.5 mm (95% within 3.0 mm) between CT and the 3D specimen and 2.5 mm (95% within 4 mm) between CT and MR. Accurate 3D registration between pathology slices and in-vivo images is feasible with an overall accuracy of approximately 2–3 mm. This will enable microscopic and macroscopic validation of anatomical and functional imaging techniques for CTV and GTV delineation in laryngeal cancer patients.

Contrast-Enhanced Anatomic Imaging as Compared to Contrast-Enhanced Tissue Characterization for Detection of Left Ventricular Thrombus

This study sought to compare contrast-enhanced anatomic imaging and contrast-enhanced tissue characterization (delayed-enhancement cardiac magnetic resonance [DE-CMR]) for left ventricular (LV) thrombus detection. Contrast echocardiography (echo) detects LV thrombus based on anatomic appearance, whereas DE-CMR imaging detects thrombus based on tissue characteristics. Although DE-CMR has been validated as an accurate technique for thrombus, its utility compared with contrast echo is unknown. Multimodality imaging was performed in 121 patients at high risk for thrombus due to myocardial infarction or heart failure. Imaging included 3 anatomic imaging techniques for thrombus detection (contrast echo, noncontrast echo, cine-CMR) and a reference of DE-CMR tissue characterization. LV structural parameters were quantified to identify markers for thrombus and predictors of additive utility of contrast-enhanced thrombus imaging. Twenty-four patients had thrombus by DE-CMR. Patients with thrombus had larger infarcts (by DE-CMR), more aneurysms, and lower LV ejection fraction (by CMR and echo) than those without thrombus. Contrast echo nearly doubled sensitivity (61% vs. 33%, p < 0.05) and yielded improved accuracy (92% vs. 82%, p < 0.01) versus noncontrast echo. Patients who derived incremental diagnostic utility from DE-CMR had lower LV ejection fraction versus those in whom noncontrast echo alone accurately assessed thrombus (35 +/- 9% vs. 42 +/- 14%, p < 0.01), with a similar trend for patients who derived incremental benefit from contrast echo (p = 0.08). Contrast echo and cine-CMR closely agreed on the diagnosis of thrombus (kappa = 0.79, p < 0.001). Thrombus prevalence was lower by contrast echo than DE-CMR (p < 0.05). Thrombus detected by DE-CMR but not by contrast echo was more likely to be mural in shape or, when apical, small in volume (p < 0.05). Echo contrast in high-risk patients markedly improves detection of LV thrombus, but does not detect a substantial number of thrombi identified by DE-CMR tissue characterization. Thrombi detected by DE-CMR but not by contrast echo are typically mural in shape or small in volume.

Update on Nuclear Medicine Imaging of Neuroendocrine Tumors

Radiolabeled tracers provide a functional imaging technique to identify neuroendocrine tumors, usually with greater sensitivity and specificity than anatomic imaging techniques such as computed tomography (CT), magnetic resonance imaging and ultrasound. Currently, there are several single-photon techniques available using either (123)I-MIBG, (111)In-DTPA-pentetreotide (Octreoscan) or (99m)Tc-EDDA/HYNIC-tyr3-octreotate. (111)In-DTPA-pentetreotide is most widely used. The best results are achieved with single-photon emission computed tomography/CT. Positron emission tomography (PET) and PET/CT are likely to provide further improvements in tumor detection, but there is, at the present time, no consensus on the choice of tracer. (18)F-FDG, (68)Ga-DOTA-TOC and (68)Ga-DOTA-NOC, (18)F-FP-Gluc-TOCA, (18)F-FDOPA and (11)C-5HTP (hydroxy tryptophan) are currently being evaluated. Early results and issues pertaining to availability are reviewed. The identification of the 'best' tracer will depend on multiple factors.