Clinical Experience with a Commercially Available Negative Oral Contrast Medium in PET/CT

Variations in clinical PET/CT operations: results of an international survey of active PET/CT users

This study gathered information about clinical PET/CT operations worldwide to help guide discussions on the use and standardization of clinical PET/CT.

METHODS

A Web-based survey of PET/CT users was initiated in November 2009 through e-mail advertising using Academy of Molecular Imaging databases. Recipients were asked 58 questions related to demographics (e.g., location, number of PET/CT systems, and staffing), PET/CT operations and use, and variations in (18)F-FDG oncology imaging protocols.

RESULTS

The responders were from centers in the Americas (71%), Europe (22%), Asia-Pacific (6%), and Middle East (1%), with most responding sites representing public health care institutions (60%). PET/CT systems were most frequently installed in nuclear medicine departments (59%). Of the sites operating a PET/CT system, 16% had 10 y or more of stand-alone PET experience. About 40% of all sites operated at least 2 PET/CT systems. PET/CT was most frequently used for applications in torso or whole-body oncology (87%), radiation therapy planning (4%), cardiology (4%), and neurology (5%). The average interval of fasting before an (18)F-FDG PET/CT examination was 7 ± 3 h (range, 4-12 h). Blood glucose levels were measured at 99% of sites, but acceptable maximal glucose levels varied substantially (an upper limit of 200 mg/dL was applied at >50% of the institutions). A weight-based radioactivity dose injection was performed at 44% of sites. The mean (18)F-FDG activity injected was 390 MBq (range, 110-585 MBq) for 3-dimensional PET of a 75-kg patient. The mean uptake time was 64 ± 14 min (range, 20-90 min). Split protocols involving patient repositioning and adapted imaging parameters were used at 51% of sites. Only 41% used patient positioning aids. Intravenous or oral CT contrast material was used at 52% of sites in up to 25% of patients. Most sites (90%) measured maximum standardized uptake value as an index of tissue glucose use. Only 62% of sites provided a fully integrated PET/CT report.

CONCLUSION

An international survey among clinical PET/CT users revealed significant variations in standard (18)F-FDG PET/CT protocols. This finding illustrates the need for continuous training and ongoing standardization in an effort to optimize PET/CT in oncology.

PET/CT (and CT) instrumentation, image reconstruction and data transfer for radiotherapy planning

The positron emission tomography in combination with CT in hybrid, cross-modality imaging systems (PET/CT) gains more and more importance as a part of the treatment-planning procedure in radiotherapy. Positron emission tomography (PET), as a integral part of nuclear medicine imaging and non-invasive imaging technique, offers the visualization and quantification of pre-selected tracer metabolism. In combination with the structural information from CT, this molecular imaging technique has great potential to support and improve the outcome of the treatment-planning procedure prior to radiotherapy. By the choice of the PET-Tracer, a variety of different metabolic processes can be visualized. First and foremost, this is the glucose metabolism of a tissue as well as for instance hypoxia or cell proliferation. This paper comprises the system characteristics of hybrid PET/CT systems. Acquisition and processing protocols are described in general and modifications to cope with the special needs in radiooncology. This starts with the different position of the patient on a special table top, continues with the use of the same fixation material as used for positioning of the patient in radiooncology while simulation and irradiation and leads to special processing protocols that include the delineation of the volumes that are subject to treatment planning and irradiation (PTV, GTV, CTV, etc.). General CT acquisition and processing parameters as well as the use of contrast enhancement of the CT are described. The possible risks and pitfalls the investigator could face during the hybrid-imaging procedure are explained and listed. The interdisciplinary use of different imaging modalities implies a increase of the volume of data created. These data need to be stored and communicated fast, safe and correct. Therefore, the DICOM-Standard provides objects and classes for this purpose (DICOM RT). Furthermore, the standard DICOM objects and classes for nuclear medicine (NM, PT) and computed tomography (CT) are used to communicate the actual image data created by the modalities. Care must be taken for data security, especially when transferring data across the (network-) borders of different hospitals. Overall, the most important precondition for successful integration of functional imaging in RT treatment planning is the goal orientated as well as close and thorough communication between nuclear medicine and radiotherapy departments on all levels of interaction (personnel, imaging protocols, GTV delineation, and selection of the data transfer method).

Evaluation of low-density neutral oral contrast material in PET/CT for tumor imaging: results of a randomized clinical trial

OBJECTIVE

The objective of this study was to determine the impact on image quality and risks in terms of artifacts and side effects of a low-density barium-based suspension as oral contrast material for CT during PET/CT examinations of an oncologic patient population.

SUBJECTS AND METHODS

Eighty-five patients (51 men and 34 women; mean age, 53 years; age range, 21-87 years) were prospectively randomized to receive either 0.1% barium sulfate oral suspension or no oral contrast material during PET/CT. Patients in the oral contrast group were given 1,350 mL over 60-75 minutes. The (18)F-FDG PET component of each examination was reviewed for the presence of artifacts by two nuclear medicine physicians and was classified as adequate (no presence of artifactual focal FDG uptake attributed to attenuation-correction errors) or inadequate (focal uptake in attenuation-correction PET images with no corresponding uptake in non-attenuation-corrected PET images). Two radiologists reviewed the CT studies and scored the degree of bowel opacification using a 5-point scale, ranging from 0 for no opacification (i.e., not possible to delineate the bowel structures from the surrounding tissues) to 4 for excellent opacification (i.e., bowel structure identifiable and bowel wall clearly visible). The attenuation values (in Hounsfield units) were recorded in the stomach, duodenum, mid jejunum, and terminal ileum for quantitative analysis. Interobserver variability was assessed using kappa coefficients.

RESULTS

None of the patients who received oral contrast material experienced side effects. All 85 PET examinations were considered adequate with no observable artifacts. The mean bowel opacification scores of the oral contrast group (2.59 and 2.93) as evaluated by radiologists 1 and 2, respectively, were significantly higher (p < 0.01) than those of the control group (1.55 and 1.59). The level of attenuation achieved in the contrast group was significantly higher than in the control group. The interobserver variability was moderate (kappa = 0.32).

CONCLUSION

The use of low-density neutral oral contrast material for CT during combined FDG PET/CT studies significantly improves visualization of the bowel structures compared with no contrast material without causing side effects or clinically detectable errors in the attenuation correction of the FDG PET study.

Bowel hot spots at PET-CT

Positron emission tomography (PET) with 2-[fluorine-18]fluoro-2-deoxy-d-glucose (FDG) has been shown to be sensitive in the detection of many bowel malignancies, but its specificity is lower because of various physiologic and pathologic patterns of bowel FDG uptake. PET-computed tomography (CT) can be useful in localizing and characterizing foci of increased FDG uptake within the bowel. As the use of PET-CT in the staging and monitoring of oncologic disease continues to expand, familiarity with these patterns of bowel FDG uptake is essential and can help determine the need for and the relative urgency of further testing. Although a variety of imaging protocols are used for PET-CT, the use of negative oral contrast agent allows improved bowel distention while eliminating potential artifacts caused by high-density oral contrast agents. In addition, correlation with the CT portion of the combined PET-CT examination can sometimes help identify the cause of focal or segmental bowel uptake. The radiologist should be aware of potential pitfalls in the evaluation of FDG-avid foci within the abdomen, including bowel motility and low-attenuation lesions mimicking bowel. Nevertheless, even though the precise role of combined PET-CT for bowel assessment has yet to be determined, the application of sound basic principles of image interpretation will help ensure the accurate interpretation of bowel findings seen with this combined modality.

Respective Roles of Thyroglobulin, Radioiodine Imaging, and Positron Emission Tomography in the Assessment of Thyroid Cancer

Depending on the iodine supply of an area, the incidence of thyroid cancer ranges between 4 and 12/100,000 per year. To detect thyroid cancer in an early stage, the assessment of thyroid nodules includes ultrasonography, ultrasonography-guided fine-needle aspiration biopsy, and conventional scintigraphic methods using (99m)Tc-pertechnetate, (99m)Tc-sestamibi or -tetrofosmin, and (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) in selected cases. After treatment of thyroid cancer, a consequent follow-up is necessary over a period of several years. For following up low-risk patients, recombinant thyroid-stimulating hormone-stimulated thyroglobulin and ultrasonography is sufficient in most cases. After total thyroidectomy and radioiodine ablation therapy, thyroid-stimulating hormone-stimulated thyroglobulin should be below the detection limit (eg, <0.5 ng/mL, R: 70-130). An increase of thyroglobulin over time is suspicious for recurrent or metastatic disease. Especially in high-risk patients, aside from the use of ultrasonography for the detection of local recurrence and cervial lymph node metastases, nuclear medicine methods such as radioiodine imaging and FDG-PET are the methods of choice for localizing metastatic disease. Radioiodine imaging detects well-differentiated recurrences and metastases with a high specificity but only moderate sensitivity. The sensitivity of radioiodine imaging depends on the activity administered. Therefore a low activity diagnostic (131)I whole-body scan (74-185 MBq) has a lower detection rate than a high activity post-therapy scan (3700-7400 MBq). In patients with low or dedifferentiated thyroid cancer and after several courses of radioiodine therapy caused by metastatic disease, iodine negative metastases may develop. In these cases, despite clearly elevated levels of thyroglobulin, radioiodine imaging is negative or demonstrates only faint iodine uptake. The method of choice to image these iodine negative metastases is FDG-PET. In recent years the combination of PET and computed tomography has been introduced. The fusion of the metabolic and morphologic information was able to increase the diagnostic accuracy, reduces pitfalls and changes therapeutic strategies in a reasonable number of patients.