Elevated uptake of F-18 FDG in PET scans in nonmalignant disease

FDG-PET/CT in the Postoperative Period: Utility, Expected Findings, Complications, and Pitfalls

FDG-PET/CT as a modality is increasingly used for detection of recurrence and for restaging in patients with clinical suspicion of malignancy, as well as in patients with elevated tumor markers. However, there are many pitfalls in the interpretation of these scans when the studies are performed after some treatment. Some of these are attributed to normal physiological distribution and are compounded when there are inflammatory changes occurring after surgery. The body's inherent response to the surgical insult results in this inflammation. In addition, there are also complications that can happen following surgery, causing increased FDG uptake. Despite various fallacies, FDG-PET/CT provides valuable information in evaluation of residual and recurrent malignant disease. In this article, we aim to describe some of these postsurgical changes secondary to inflammation, common surgical complications, and finally, the utility of FDG-PET/CT in these patients to detect recurrent disease, even in the background of postsurgical changes.

18F-FDG PET/CT imaging in oncology

Accurate diagnosis and staging are essential for the optimal management of cancer patients. Positron emission tomography with 2-deoxy-2-[fluorine-18]fluoro-D-glucose integrated with computed tomography (18F-FDG PET/CT) has emerged as a powerful imaging tool for the detection of various cancers. The combined acquisition of PET and CT has synergistic advantages over PET or CT alone and minimizes their individual limitations. It is a valuable tool for staging and restaging of some tumors and has an important role in the detection of recurrence in asymptomatic patients with rising tumor marker levels and patients with negative or equivocal findings on conventional imaging techniques. It also allows for monitoring response to therapy and permitting timely modification of therapeutic regimens. In about 27% of the patients, the course of management is changed. This review provides guidance for oncologists/radiotherapists and clinical and surgical specialists on the use of 18F-FDG PET/CT in oncology.

Correcting tumour SUV for enhanced bone marrow uptake: retrospective 18F-FDG PET/CT studies

PURPOSE

The concentration of F-FDG in the bone marrow is usually low. One common cause of high uptake is due to bone marrow stimulating drugs administered in conjunction with chemotherapy or radiation therapy. It has been hypothesized that the sequestration of F-FDG to the bone marrow may reduce the standardized uptake value (SUV) of a tumour. We tested this hypothesis by quantifying total F-FDG uptake in the bone marrow of patients with visibly enhanced bone marrow uptake and computing its effect on tumour SUV.

METHODS

Total F-FDG in bone marrow was measured in two groups of PET/CT studies: one (n=19) with visibly enhanced bone marrow, the other (n=5), a baseline group with 'normal' levels of uptake. To measure the F-FDG in bone marrow, the entire skeleton in the CT was segmented from surrounding tissue, and the resulting volume applied to the PET image. Using kinetic analysis we show that the predicted correction factor to tumour SUV is given by (1-q0/Q)/(1-q/Q), where Q is the injected dose, and q and q0 are enhanced and baseline bone marrow uptake (MBq).

RESULTS

The enhanced bone marrow uptake averaged 8.9+/-3.2% of injected dose (15.2% max) vs. 4.2+/-0.4% (4.6% max) at baseline. This resulted in a predicted artificial decrease in tumour SUV of up to 11.5% (4.9+/-4.3%, on average).

CONCLUSION

Enhanced bone marrow uptake is predicted to reduce tumour SUVs by as much as 11.5% in our patient group and is a potential confounding factor in using SUV for monitoring tumour response to therapy.

18F-FDG PET/CT in the evaluation of recurrent ovarian cancer: a prospective study on forty-one patients

AIM

Many patients with ovarian cancer are at high risk of recurrence especially in the 2 years following first-line therapy. CA125 serum levels measurement associated to computed tomography (CT), ultrasound (US) and magnetic resonance imaging (MRI) are currently used during follow-up to detect recurrent disease. Unfortunately, in a relevant percentage of cases all of these traditional imaging techniques provide a significant number of doubtful/equivocal results or turn out negative even in presence of elevated Ca125 levels. Aim of our study was to evaluate sensitivity, specificity and accuracy of (18)F-FDG PET/CT in a group of patients with suspicion of ovarian cancer recurrence.

METHODS

We prospectively evaluated 41 patients with a mean age of 59.4 years who had been previously treated for ovarian cancer with surgery and radio-chemotherapy or radio-chemotherapy alone. Following the performance of traditional radiologic imaging (US, CT, MRI) and Ca125 measurement, all patients underwent additional (18)F-FDG PET/CT. PET/CT results were compared with histologic findings or clinical, laboratory and repeated traditional imaging techniques during subsequent follow-up data.

RESULTS

Of 41 patients 32 had a positive PET-CT (30 true positive, two false positive) whereas nine a negative PET/CT (five true negative, four false negative). Overall, in our experience (18)F-FDG PET/CT provided a good sensitivity (88.2%), specificity (71.4%) and accuracy (85.4%), superior to that reported in literature for traditional radiologic imaging.

CONCLUSIONS

It can be concluded that (18)F-FDG PET/CT appears to be a useful and accurate tool in disclosing early recurrent ovarian cancer.

Clinical applications of PET in oncology

Positron emission tomography (PET) provides metabolic information that has been documented to be useful in patient care. The properties of positron decay permit accurate imaging of the distribution of positron-emitting radiopharmaceuticals. The wide array of positron-emitting radiopharmaceuticals has been used to characterize multiple physiologic and pathologic states. PET is used for characterizing brain disorders such as Alzheimer disease and epilepsy and cardiac disorders such as coronary artery disease and myocardial viability. The neurologic and cardiac applications of PET are not covered in this review. The major utilization of PET clinically is in oncology and consists of imaging the distribution of fluorine 18 fluorodeoxyglucose (FDG). FDG, an analogue of glucose, accumulates in most tumors in a greater amount than it does in normal tissue. FDG PET is being used in diagnosis and follow-up of several malignancies, and the list of articles supporting its use continues to grow. In this review, the physics and instrumentation aspects of PET are described. Many of the clinical applications in oncology are mature and readily covered by third-party payers. Other applications are being used clinically but have not been as carefully evaluated in the literature, and these applications may not be covered by third-party payers. The developing applications of PET are included in this review.

Diffuse Bone Marrow Uptake on Whole-Body F-18 Fluorodeoxyglucose Positron Emission Tomography in a Patient Taking Recombinant Erythropoietin

F-18 fluorodeoxyglucose (FDG)-positron emission tomography (PET) is used extensively in oncology to diagnose, stage, and restage patients with various malignancies. Many patients treated for malignancies develop neutropenia secondary to marrow suppressive chemotherapy and are subsequently treated with synthetic hematopoietic growth factors (HGF), both granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte-colony-stimulating factor (G-CSF). Patients taking HGF can present a diagnostic challenge for those interpreting PET because they can demonstrate diffuse marrow uptake on FDG-PET scans, mimicking diffuse bone marrow metastases. It has not been reported whether bone marrow uptake is affected on PET scans in patients taking erythropoietin, the erythroid-specific cell-line stimulator. We report a case of extensive diffuse bone marrow uptake in a 77-year-old man with a history of colon cancer who began taking erythropoietin 3 weeks before his PET scan. This case demonstrates the need to consider erythropoietin in the differential diagnosis of possible etiologies causing diffuse bone marrow uptake on PET scans.