Søren Hess

The Pivotal Role of FDG-PET/CT in Modern Medicine

The technology behind positron emission tomography (PET) and the most widely used tracer, 2-deoxy-2-[18F]fluoro-D-glucose (FDG), were both conceived in the 1970s, but the latest decade has witnessed a rapid emergence of FDG-PET as an effective imaging technique. This is not least due to the emergence of hybrid scanners combining PET with computed tomography (PET/CT). Molecular imaging has enormous potential for advancing biological research and patient care, and FDG-PET/CT is currently the most widely used technology in this domain. In this review, we discuss contemporary applications of FDG-PET and FDG-PET/CT as well as novel developments in quantification and potential future indications including the emerging new modality PET/magnetic resonance imaging.

An Update on Novel Quantitative Techniques in the Context of Evolving Whole-Body PET Imaging

Since its foundation PET has established itself as one of the standard imaging modalities enabling the quantitative assessment of molecular targets in vivo. In the past two decades, quantitative PET has become a necessity in clinical oncology. Despite introduction of various measures for quantification and correction of PET parameters, there is debate on the selection of the appropriate methodology in specific diseases and conditions. In this review, we have focused on these techniques with special attention to topics such as static and dynamic whole body PET imaging, tracer kinetic modeling, global disease burden, texture analysis and radiomics, dual time point imaging and partial volume correction.

PET/CT without capacity limitations: a Danish experience from a European perspective

ObjectivesWe report the 3-year clinical experience of a large new Danish PET/CT centre without capacity limitations in relation to national and European developments.MethodsThe use of PET/CT in cancer was registered from early 2006 to early 2009 to judge the impact on patient management and to compare it with national and European trends.Results6056 PET/CT examinations were performed in 4327 patients. Activity increased by 86 examinations per month compared with the same month the year before. Referrals came primarily from oncology (23.0%), haematology (21.6%), surgery (12.6%), internal medicine (12.7%) and gynaecology (5.5%). Referral indications were diagnosis (31.3%), staging (22.3%), recurrence detection (21.2%), response evaluation (17.0%) and other (8.2%). Response from nearly 60% of users showed that PET/CT caused a change in diagnosis and/or staging and/or treatment plan in 36.0% of cases. During the study period, there was a steep increase in the national use of FDG and in the European use of PET/CT.ConclusionsWe recorded a constantly increasing use of PET/CT that caused a change in diagnosis and/or staging and/or treatment plan in 36.0% of cases. In line with national and European trends this may suggest a shift in favour of functional rather than anatomical imaging.

FDG-PET/CT in Infectious and Inflammatory Diseases

Nuclear medicine techniques have been an integral part of infection and inflammation imaging for decades; in recent years, fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) has taken over many indications. This review provides a comprehensive overview of the current and potential applications for FDG-PET/CT in infectious and inflammatory diseases (ie, systemic infections, bone infections, vascular infection and inflammation, thoracic and abdominal inflammation) and potential novel applications in both infection and inflammation.

FDG PET/CT methodology for evaluation of treatment response in lymphoma: from "graded visual analysis" and "semiquantitative SUVmax" to global disease burden assessment

Dear Sir, In recent years, there have been multiple endeavours by various investigators [1–4] seeking to show the importance of semiquantitative analysis of PET data using conventional metrics (e.g. ΔSUVmax) and its superiority over the international prognosis score for prediction of overall outcome and progression-free survival. We agree with these investigators that molecular imaging using FDG PET plays a pivotal role in risk stratification in treatment individualization. While these endeavours are important steps in PET/CT imaging for disease assessment and prognostication, we would like to share our views on the relevance of emerging PET metrics that have the potential to replace existing ones in the near future for optimal patient management [5]. Its use in the interim assessment of chemotherapeutic response has been one of the major strengths of FDG PET/CT, and it has been widely used for this purpose in the management of lymphoma to tailor the treatment regimen as well as to predict disease prognosis and overall outcome. This is now the standard of care in most centres where FDG PET/ CT is available. While the utility of FDG PET/CT imaging in lymphoma has been generally recognized, there has been continuing debate on the appropriate PET methodology and the most reliable parameter to interpret the therapeutic response, particularly in mid-cycle. Beyond doubt, visual analysis remains an integral component of the assessment, but there has been persistent endeavour by both oncologists and physicians interpreting PET to define an objective set of parameters, the most common ones being the Deauville criteria for interim response assessment [6]. It has recently been proposed that these criteria be extended to the end of treatment remission assessment, although still based entirely on visual and not quantitative interpretation [7]. In complete metabolic response, visual interpretation is relatively straightforward, whereas in partial response of lesser grade or even in progressive metabolic disease assessment needs more objectivity. In the recommendation of the Imaging Subcommittee of the International Harmonization Project in Lymphoma, mediastinal blood pool activity is considered as reference background activity for interpreting PET positivity for a residual mass equal to or more than 2 cm in greatest transverse diameter. For smaller lesions or for normal sized lymph nodes, uptake more than surrounding background is considered positive [8]. While these criteria have been used in different centres for response assessment, it has been increasingly felt by physicians interpreting PET that visual grading or single point SUVmax measurement is inadequate for appropriate assessment, particularly in malignancies such as lymphoma. There has been some work demonstrating that introducing quantification by measuring SUVmax leads to improvement [1], since changes in this value (ΔSUVmax) were S. Basu Radiation Medicine Centre, Bhabha Atomic Research Centre, Tata Memorial Hospital Annexe, Jerbai Wadia Road, Parel, Mumbai 400 012, India

Efficacy of FDG PET/CT imaging for venous thromboembolic disorders: preliminary results from a prospective, observational pilot study.

Purpose In recent years, several case reports have described venous thromboembolism (VTE) on FDG PET/CT. In this short communication, we present results from a proof-of-concept pilot study aimed at providing some preliminary data on the efficacy of FDG PET/CT in prospective patients with suspected VTE. Patients and Methods Fifteen patients with suspected deep venous thrombosis (DVT) and/or pulmonary embolism (PE) were included prospectively and underwent a whole-body FDG PET/CT. Patients were divided into 4 groups as follows: DVT+ (DVT proven by high clinical suspicion and positive compression ultrasound), DVT− (DVT ruled out by low clinical suspicion and negative compression ultrasound), PE+ (PE proven by high clinical suspicion and positive lung scintigraphy), and PE− (PE ruled out by low clinical suspicion and normal lung scintigraphy). Images were interpreted visually by 2 experienced nuclear medicine physicians independently and without knowledge of other imaging results. Results Seven DVT+, 6 DVT−, 6 PE+, and 1 PE− were included. Five patients were suspected of both DVT and PE. FDG PET/CT correctly diagnosed the presence or lack of DVT in all patients, whereas results are more ambiguous in PE with only 2 of 6 PE patients showing FDG avidity. The readers agreed in all cases. Conclusions Although further studies are warranted for further clarification, our preliminary data substantiate that FDG PET/CT is a viable modality for assessing VTE, at least for DVT. We believe our results add positively to the limited data on this subject and are promising enough to warrant further larger series.

The Basic Principles of FDG-PET/CT Imaging

Positron emission tomography (PET) imaging with 2-[(18)F]fluoro-2-deoxy-D-glucose (FDG) forms the basis of molecular imaging. FDG-PET imaging is a multidisciplinary undertaking that requires close interdisciplinary collaboration in a broad team comprising physicians, technologists, secretaries, radio-chemists, hospital physicists, molecular biologists, engineers, and cyclotron technicians. The aim of this review is to provide a brief overview of important basic issues and considerations pivotal to successful patient examinations, including basic physics, instrumentation, radiochemistry, molecular and cell biology, patient preparation, normal distribution of tracer, and potential interpretive pitfalls.

18F-FDG-PET/CT in fever of unknown origin: clinical value

ObjectiveFever of unknown origin continues to be a diagnostic challenge for clinicians. The aim of this study was to confirm whether 18F-fluorodeoxyglucose (18F-FDG)-PET/computed tomography (CT) is a helpful tool in patients suffering from this condition. Patients and methodsFifty-seven patients with fever of unknown origin were examined with 18F-FDG-PET/CT as part of their diagnostic workup at the clinicians’ discretion. The medical records were read retrospectively to establish the final diagnosis and evaluate the degree to which PET/CT contributed to the diagnosis. ResultsThe examination was considered helpful if it corresponded to the final diagnosis by showing uptake in an organ considered responsible for the condition, or if it was without focal findings, thereby excluding the patient from having focal infection or malignancy. It was perceived false positive if it pointed towards an organ not regarded by the clinicians as being related to the final diagnosis. It was perceived not helpful if the cause of fever was not visible on 18F-FDG-PET/CT.We found 18F-FDG-PET/CT helpful in 75% of patients, not helpful in 4%, and false positive in 21% of patients. Conclusion18F-FDG-PET/CT is a useful tool in the investigation of fever of unknown origin; it can reduce patient inconvenience and possibly costs to society if used earlier in the diagnostic process.

Tumor thrombus: ancillary findings on FDG PET/CT in an oncologic population.

Purpose Thrombosis in cancer may manifest itself as venous thromboembolic disease or tumor thrombosis (TT). We present our experience with incidentally detected TT on FDG PET/CT in 21 oncologic patients. Patients and Methods We retrospectively reviewed all FDG PET/CT examinations during a 5-year period at the Army Hospital Research and Referral in New Delhi, India, and included all oncology cases with FDG-avid thrombosis in the report. The diagnosis of TT was based on FDG-avid solid masses inside the vessels in patients with known malignancy. The SUVmax was calculated. Results Twenty-one patients were included; the most common malignancies were renal cell carcinoma (n = 6), hepatocellular carcinoma (n = 3), and lung cancer (n = 3). Indication for the scan was initial staging (n = 15) and suspected recurrence (n = 6). Several vessels were affected, the most common was the inferior vena cava (n = 14), but most other major branches of the venous vasculature was represented, and some patients had thrombi in several vessels. FDG uptake was linear in 7 patients, linear with a dilated vessel in 6 patients, and focal in 7 patients. The mean SUVmax of the primary tumors was 10.3 (range, 2.6–31.2; median, 6.9), and the mean SUVmax of the thrombi was 7.85 (range, 1.7–23.2; median, 6.1). All but 2 patients had additional FDG-avid foci besides the thrombus. Conclusions This study supports results from other smaller studies regarding the usefulness of FDG PET/CT in TT and corroborates the hypothesis that the SUVmax and the patterns of FDG uptake can be helpful for differentiating BT from TT in oncological patients.

A brief overview of novel approaches to FDG PET imaging and quantification

The widespread implementation of hybrid FDG PET/CT worldwide has brought about a paradigm shift in the use of diagnostic imaging—molecular imaging combining morphological and functional data is now at the forefront of patient management in many clinical settings, not only for initial diagnosis, staging, monitoring of response to treatment and detection of recurrence, but also for prognostication and disease characterization. Although developments have focused particularly on the qualitative visual analysis of images, FDG PET allows elaborate quantification, which should be explored much more in the future and ideally standardized worldwide. In this brief overview, we outline the state of the art of novel and quantitative approaches to FDG imaging, i.e. standard uptake value, partial volume effect and partial volume correction, multiple-time-point imaging, assessment of global disease burden and PET/MRI, all of which we expect to see evolving as powerful tools in the coming years and enhancing sensitivity and specificity in variety of clinical settings, in which FDG PET imaging has not yet shown its full potential.