Tumor lesion detection: when is integrated positron emission tomography/computed tomography more accurate than side-by-side interpretation of positron emission tomography and computed tomography?

OBJECTIVES: To determine if there is added value to oncology studies performed with a dedicated in-line positron emission tomography (PET)/computed tomography (CT) scanner as compared with PET read side by side with diagnostic CT (DCT). METHODS: Forty-one consecutive oncology patients referred for PET/CT who had contemporary DCT scans for review were enrolled. Body regions assessed on a DCT scan were assessed on PET/CT and by side-by-side reading of PET and DCT (SBS PET/DCT). Lesions identified on DCT, the CT portion of PET/CT, SBS PET/DCT, and the reading of fused PET/CT images were scored as benign or malignant. The PET portion of the PET/CT study was read by 2 teams: the first read the SBS PET/DCT scan and the other read the complete fused PET/CT scan. For discordant lesions, the final diagnosis was determined by pathologic findings (n = 6) or imaging follow-up (n = 21). RESULTS: Twenty-seven (16.1%) of the 168 lesions were discordant when comparing analysis of fused PET/CT and SBS PET/DCT. Sixteen (9.5%) were fundamentally discordant, and 11(6.6%) were discordant in degree of confidence. For all discordant lesions only, the sensitivity, specificity, negative predictive value, positive predictive value, and accuracy for PET/CT were 100%, 33%, 100%, 94%, and 78%, respectively, and for SBS PET/DCT, they were 38%, 50%, 19%, 73%, and 30%, respectively (P < 0.001 for sensitivity, P = not specific for specificity). The 2 main causes for misclassification on SBS PET/DCT were incorrect localization (n = 12) and changes occurring in the time gap between DCT and PET/CT (n = 4). CONCLUSIONS: In-line PET/CT offers better lesion localization in comparison to the visual fusion of PET and CT, especially for small lymph nodes, lesions adjacent to mobile organs, or lesions adjacent to the chest or abdominal wall.     

A novel phantom design for emission tomography enabling scatter- and attenuation-”free” single-photon emission tomography imaging

A newly designed technique for experimental single-photon emission tomography (SPET) and positron emission tomography (PET) data acquisition with minor disturbing effects from scatter and attenuation has been developed. In principle, the method is based on discrete sampling of the radioactivity distribution in 3D objects by means of equidistant 2D planes. The starting point is a set of digitised 2D sections representing the radioactivity distribution of the 3D object. Having a radioactivity-related grey scale, the 2D images are printed on paper sheets using radioactive ink. The radioactive sheets can be shaped to the outline of the object and stacked into a 3D structure with air or some arbitrary dense material in between. For this work, equidistantly spaced transverse images of a uniform cylindrical phantom and of the digitised Hoffman rCBF phantom were selected and printed out on paper sheets. The uniform radioactivity sheets were imaged on the surface of a low-energy ultra-high-resolution collimator (4 mm full-width at half-maximum) of a three-headed SPET camera. The reproducibility was 0.7% and the uniformity was 1.2%. Each rCBF sheet, containing between 8.3 and 80 MBq of ^99mTcO₄ ^– depending on size, was first imaged on the collimator and then stacked into a 3D structure with constant 12 mm air spacing between the slices. SPET was performed with the sheets perpendicular to the central axis of the camera. The total weight of the stacked rCBF phantom in air was 63 g, giving a scatter contribution comparable to that of a point source in air. The overall attenuation losses were <20%. A second SPET study was performed with 12-mm polystyrene plates in between the radioactive sheets. With polystyrene plates, the total phantom weight was 2300 g, giving a scatter and attenuation magnitude similar to that of a patient study. With the proposed technique, it is possible to obtain ”ideal” experimental images (essentially built up by primary photons) for comparison with ”real” images degraded by photon scattering and attenuation losses. The method can serve as a tool for experimental validation and intercomparison of attenuation and scatter correction methods. Moreover, the large flexibility of this phantom design will allow investigations of arbitrary activity distributions and autoradiography or other imaging techniques such as PET, x-ray computed tomography or magnetic resonance imaging. Received 8 August and in revised form 21 September 1999     

FDG positron emission tomography/computed tomography studies of Wilms’ tumor

Purpose  

The purpose of this analysis was to evaluate the utility of FDG PET/CT scanning in patients with Wilms’ tumors.     

Evaluation of Wegener’s granulomatosis using 18F-fluorodeoxyglucose positron emission tomography/computed tomography

Objective

Wegener’s granulomatosis (WG) is a relatively rare disease characterized by granulomatous necrotizing vasculitis that primarily involves small- and medium-sized vessels. Systemic findings observed on ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) have not been well reported. The purpose of this study was to evaluate the FDG PET/CT imaging in the diagnosis and follow-up of patients with WG.

Materials and methods

Thirteen FDG PET/CT images obtained for 8 patients (2 men and 6 women) with WG were retrospectively analyzed. Of these, 6 were performed for diagnosis, 2 for restaging and follow-up, and 5 for assessment of treatment efficacy. Maximum standardized uptake values (max SUVs) and visual analyses were used to interpret the FDG PET/CT images. In addition, nonenhanced CT findings obtained during FDG PET/CT were described.

Results

WG lesions of the upper respiratory tract and lung were more clearly detected by FDG PET/CT fusion imaging than by nonenhanced CT alone, and all of the active lesions showed decreased FDG uptake after treatment. In addition, FDG PET/CT can provide complementary information to indicate biopsy site based on FDG uptakes.

Conclusions

FDG PET/CT is a feasible modality for evaluating lesion activities, therapeutic monitoring, and follow-up of WG. Furthermore, biopsy sites of WG lesions may be determined by FDG PET/CT.     

¹⁸F-Fluoro-2-deoxyglucose positron emission tomography in cardiac sarcoidosis

Cardiac sarcoidosis (CS) is a rare and potentially life-threatening disease that causes conduction disturbance, systolic dysfunction, and most notably sudden cardiac death. Accurate diagnosis of CS is thus mandatory; however, a reliable approach that enables diagnosis of CS with high sensitivity and specificity has yet to be established. Recent studies have demonstrated the promising potential of ¹⁸F-fluoro-2-deoxyglucose positron emission tomography (¹⁸F-FDG PET) in the diagnosis and assessment of CS. Indeed, ¹⁸F-FDG PET provides a wide variety of advantages over previous imaging modalities; however, there are pitfalls and limitations that should be recognized. In this review article, (1) the rationale for ¹⁸F-FDG PET application in CS, (2) suitable pretest preparations, and (3) evaluation protocols for the ¹⁸F-FDG PET images obtained will be addressed. In particular, sufficient suppression of physiological ¹⁸F-FDG uptake in the heart is essential for accurate assessment of CS. Also, (4) recent studies addressing the diagnostic role of ¹⁸F-FDG PET and (5) the clinically important differences between ¹⁸F-FDG PET and other imaging technologies will be reviewed. For example, active sarcoid lesions and their response to steroid treatment will be better detected by ¹⁸F-FDG PET, whereas fibrotic lesions might be shown more clearly by magnetic resonance imaging or other nuclear myocardial perfusion imaging. In the last decade, ¹⁸F-FDG PET has substantially enhanced detection of CS; however, CS would be better evaluated by a combination of multiple modalities. In the future, advances in ¹⁸F-FDG PET and other emerging imaging modalities are expected to enable better management of patients with sarcoidosis.     

Is contrast material needed after treatment of malignant lymphoma in positron emission tomography/computed tomography?

Purpose  

Positron emission tomography (PET)/computed tomography (CT) with ¹⁸F-fluorodeoxyglucose is widely used for post-therapeutic surveillance of malignant lymphoma. Debate still exists as to whether intravenous contrast media during the CT stage of a PET/CT scan should be used. The purpose of this study was to investigate the clinical value of contrast agent in PET/CT in patients with lymphoma following treatment.     

Radiopharmaceuticals for positron emission tomography investigations of Alzheimer’s disease

Alzheimer’s disease (AD) is a common degenerative neurological disease that is an increasing medical, economical, and social problem. There is evidence that a long “asymptomatic” phase of the disease exists where functional changes in the brain are present, but structural imaging for instance with magnetic resonance imaging remains normal. Positron emission tomography (PET) is one of the tools by which it is possible to explore changes in cerebral blood flow and metabolism and the functioning of different neurotransmitter systems. More recently, investigation of protein aggregations such as amyloid deposits or neurofibrillary tangles containing tau-protein has become possible. The purpose of this paper is to review the current knowledge on various ¹⁸F- and ¹¹C-labelled PET tracers that could be used to study the pathophysiology of AD, to be used in the early or differential diagnosis or to be used in development of treatment and in monitoring of treatment effects.     

Can fluorine-18-fluorodeoxyglucose positron emission tomography/computed tomography detect hepatocellular carcinoma and its extrahepatic metastases?

Aims

The point of this research is to investigate the potential role of (18-F-FDG/PET) in the identification of hepatocellular carcinoma (HCC) and its metastases.

Is hybridic positron emission tomography/computerized tomography the only option? The future of nuclear medicine and molecular imaging

As we all know, Nuclear Medicine is the medical science using nuclear radiation for diagnosis, treatment and research. Nuclear Medicine, in contrast to Radiology, makes use of unsealed sources of radiation. Nuclear Medicine a few years ago has partly offered Nuclear Cardiology, the most lucrative of all Nuclear Medicine "children" at that time, to Cardiology. Radiology, has succeeded in being recognized by the European Union Authorities as Clinical Radiology. The word "clinical" offers greater independence to Clinical Radiology and makes it difficult for such a specialty to relinquish any of its equipment i.e. the diagnostic CT scan or the newly developed fast angiography CT, to other specialties. Contrary to Clinical Radiology, Nuclear Medicine being a laboratory specialty in most countries seems to have no right to deny offering, after some period of "proper certified education", its PET camera to Clinical Radiologists. Nuclear Medicine by virtue of its unique diagnostic techniques and treatments, is and should be recognized as a "Clinical Specialty" The interference of other specialties in the fields of Nuclear Medicine is also indicated by the fact that in vitro techniques of Nuclear Medicine are often used by Endocrinologists and Oncologists in their own laboratories. Also in some hospitals the Director of the Radiology Department acts as the Director of Nuclear Medicine Laboratory. Finally at present, Radiologists wish after "proper certified education", to be on equal terms in charge of the new hybridic equipment, the PET/CT scanner. If that is followed to happen, Nuclear Medicine will be in a difficult position losing at least part of PET and consequently should ask for help from its "Overlords and Protectors" i.e. the National and the European Societies of Nuclear Medicine and the Society of Nuclear Medicine of the United States of America. Radiology as a specialty participating om equal terms with the PET camera will then include the study of: a) "open sources of radiation" b) nuclear radiation and c) molecular nuclear medicine. The "European Journal of Nuclear Medicine and Molecular Imaging" shall have to erase the three last words of its title and be renamed. As Professor Abass Alavi et al (2007), have mentioned: "Is PET/CT the only option?" In favor of PET/CT are the following: Attenuation correction (AC) and better anatomical localization of lesions visualized with PET. Also PET/CT can be used as a diagnostic CT scanner (dCT). Against using the PET/CT scanners are the following arguments: a) This equipment is not necessary because we can always ask the Radiologists for a dCT scan. Many patients have already done a dCT scan at the time they are referred for a PET scan to the Nuclear Medicine Department. b) The absolute clinical indications for PET/CT with the use of a contrast agent, are under investigation. c) Although there is at present a list of indications suggested for the PET/CT scanner, there are studies disputing some of these indications, as for example in metastatic colon cancer where a high diagnostic accuracy for PET study alone, has been reported. d) The option of AC performed by the PET/CT scanner has also been questioned. Artifacts may be up to 84%. e) The PET/CT is expensive, time consuming, space occupying, and needs additional medical and technical personnel. f) Not to mention the extra radiation dose to the patients. g) Shall we inform those young medical students who wish to become nuclear medicine physicians, to hold their decision till the content of future Nuclear Medicine is clarified? We may suggest that: Our specialty could be renamed as: "Clinical Nuclear Medicine" and include additional "proper certified education" on the PET/CT equipment. The PET/CT scanner should remain in the Nuclear Medicine Department where Radiologists could act as advisors.     

“W-shaped” volume curve with gated myocardial perfusion single photon emission computed tomography

OBJECTIVES: Gating errors (GEs) with ECG gated myocardial SPECT (G-SPECT) may occur irrespective of the presence or absence of arrhythmias. We evaluated the impact of GEs on both reconstructed tomograms and left ventricular ejection fraction (LVEF) derived from G-SPECT, and searched for clues to identify these errors. METHODS: We studied 2 GE patients, 10 normal subjects (NLs), and 10 atrial fibrillation patients. Stress technetium-99m sestamibi G-SPECT was performed. Left ventricular (LV) contraction was evaluated in the beating slices. LVEF was calculated with G-SPECT using QGS (Cedars-Sinai, Los Angels) and p-FAST (Sapporo Medical University, Japan), and compared with that obtained by echocardiography (ECHO). LV volume curves were created by QGS and p-FAST. The heart rates (HRs) were calculated from the acquired images, and compared with their resting HRs. The mean count density of the myocardium was measured and time-activity curves were created. RESULTS: In patients with GEs, bi-phasic LV contraction was demonstrated with fading-out towards end-diastole. G-SPECT underestimated LVEF compared to ECHO by 10% or more. The volume curves appeared "W-shaped." The HRs from the images were slower than the resting HRs. The count density decrement from frame #1 to #8 was larger than that of NLs. The time-activity curves were different in shape from those of NLs. CONCLUSIONS: G-SPECT underestimates LVEF in patients with GEs. These errors can be identified with a combination of visual inspection of beating slices, time-volume curves, and time-activity curves. Monitoring the HR is a clue for anticipating and avoiding these errors.     

Oestrogen-related tumour phenotype: positron emission tomography characterisation with ¹⁸F-FDG and ¹⁸F-FES

This article outlines the role of 16α-[(18)F]fluoro-17β-oestradiol ((18)F-FES) positron emission tomography (PET) combined with 2-[(18)F]fluoro-2-deoxy-D-glucose ((18)F-FDG) in patients with oestrogen-related tumours for evaluating tumour phenotype. (18)F-FES-PET combined with (18)F-FDG is helpful in characterising the distinct phenotypic features of oestrogen-related tumours; that is, inter- and intrapatient tumour heterogeneity, which indicates its great potential as a determinant of individualised treatment and a prognostic predictor for patients with oestrogen-related tumours.     

FDG positron emission tomography in head and neck cancer: pitfall or pathology?

PURPOSE: Fluorodeoxyglucose (FDG) positron emission tomography (PET) is a functional imaging technique used for imaging and staging malignant diseases. In many oncologic situations, however, abnormal changes seen on the PET studies are not caused by tumor, which is especially true in the head and neck region. The authors present an overview of the phenomena that may confound the interpretation of the images in head and neck cancer. MATERIALS AND METHODS: FDG PET studies were performed in patients with primary head and neck cancer and in patients in whom recurrent disease was likely. The results were correlated with clinical findings. Eight solitary cases were selected from a total of 180 patients studied. RESULTS AND CONCLUSIONS: Benign lesions and iatrogenic and physiologic changes may show increased FDG uptake. Therefore, clinical information on previous surgical interventions and optimal patient preparation are necessary for adequate interpretation. If these prerequisites can be met, benign lesions appear to be the only lesions that may interfere with the specificity of FDG PET.     

Combined single-photon emission computerized tomography and conventional computerized tomography (SPECT/CT): clinical value for the knee surgeons?

Single-photon emission computerized tomography in combination with conventional computer tomography (SPECT/CT) is an emerging technology that may hold great clinical value to the orthopaedic knee surgeon. Post-operative knee pain is a familiar condition seen in most orthopaedic clinics. Here, we present the value of SPECT/CT in three such cases of pain after surgical treatment of knee osteoarthritis (high tibial osteotomy, medial unicompartmental arthroplasty, total knee arthroplasty). In these patients with post-operative knee pain, SPECT/CT has proved to be beneficial in establishing the diagnosis and providing guidance for further treatment.     

Positron emission tomography/magnetic resonance imaging: the next generation of multimodality imaging?

Multimodal imaging is now well-established in routine clinical practice. Especially in the field of nuclear medicine, new positron emission tomography (PET) installations comprise almost exclusively combined PET/computed tomography (CT) scanners rather than PET-only systems. However, PET/CT has certain notable shortcomings, including the inability to perform simultaneous data acquisition and the significant radiation dose to the patient contributed by CT. Magnetic resonance imaging (MRI) offers, compared with CT, better contrast among soft tissues as well as functional-imaging capabilities. Therefore, the combination of PET with MRI provides many advantages that go far beyond simply combining functional PET information with structural MRI information. Many technical challenges, including possible interference between these modalities, have to be solved when combining PET and MRI, and various approaches have been adapted to resolving these issues. Here, we present an overview of current working prototypes of combined PET/MRI scanners from different groups. In addition, besides PET/MRI images of mice, the first such images of a rat acquired with the first commercial clinical PET/MRI scanner, are presented. The combination of PET and MRI is a promising tool in preclinical research and will certainly progress to clinical application.