Proper patient preparation and scanning protocol are needed for optimal diagnostic accuracy. Considerations that are unique to FDG-PET/CT systems include bowel preparation techniques, reduction of FDG activity in the urinary bladder, and reconstruction techniques to minimize metallic artifacts.

Bowel definition can be enhanced by using low-density barium for oral contrast material at CT, which does not cause significant artifacts at FDG-PET [11]. Oral hydration is recommended as long as the fluids do not contain glucose.

It is also important to reduce FDG accumulation within the urinary bladder. The patient is asked to void completely immediately prior to the start of scanning and by imaging the pelvis early in the study.

Metallic prostheses can cause foci of apparent increased FDG uptake due to attenuation correction [12]. This artifact can be reduced by minimizing patient motion. When CT is used for attenuation correction, an attenuation-weighted iterative reconstruction technique can also be used to minimize this artifact, although more studies are needed to optimize reconstruction factors such as segmentation, number of iterative steps, and preprocessing of attenuation date [12]. At our institution, an ordered subset expectation maximum iterative reconstruction algorithm with three iterations and 21 subsets is used. Examination of non-attenuation-corrected images is also very helpful in avoiding this pitfall.

Imaging technique at our institution for FDG-PET/CT is described in the following paragraphs and summarized in Table 1.

The patient is asked to take nothing by mouth for at least 4 h prior to examination. Upon the patient’s arrival at the radiology department, his or her weight and height are obtained and a weight-based (0.22 mCi/kg [8.1 MBq/kg]) dose of FDG is prepared. A 22- or 24-gauge intravenous line is placed, usually in the upper extremity contralateral to any prior surgery (e.g., lymph node resection) to ensure proper distribution of radiotracer. The patient’s blood glucose is determined to ensure that he or she is not hyperglycemic. At our institution, a serum glucose level of 200 mg/dL is used as a maximum cutoff point. One hour prior to imaging, the FDG dose is injected and 450 mL of low-density barium (Read-Cat 2.1 % weight/volume barium sulfate suspension; E-Z EM, Lake Success, NY) is administered orally for the patient to drink as a glucose-free solution. The patient is then placed in a quiet, dimly lit room for the remainder of the uptake phase. To minimize skeletal muscle uptake during this period, the patient is instructed not to talk and to keep the arms at the sides and the legs uncrossed. Just prior to the start of scanning, the patient is asked to void completely to minimize bladder activity.

For scanning, the patient is positioned supine and head first on a PET/CT system with a single gantry and table. The arms are raised above the head (if the patient can tolerate this position), and he or she is allowed to breathe quietly. CT is performed first. At our institution, a 64-section multidetector Siemens Biography PET/CT system is used with the following parameters: detector row configuration of 2 × 2 mm, 120 kVp, weight-adjusted milliampere-second mean 200 mAs, gantry rotation speed of 0.5 s per revolution, and pitch of 1.75. A tomogram is used to adjust the FOV so that it extends from the skull base to the midthigh. The images are reconstructed on a 512 × 512 matrix with a 70-cm FOV.

After CT is completed, the table is moved into the PET scanner. The images are acquired in a caudal-to-cranial direction from the midthigh to the skull base to minimize bladder filling. Three-minute emission acquisitions per FOV are obtained in three-dimensional mode. Transverse PET scans are obtained per FOV, with a section thickness of 2 mm. Five to seven table positions are usually needed, with each position allowing coverage of 17.0 cm. The PET scans are reconstructed on 168 × 168 matrix, with an ordered subset expectation maximum iterative reconstruction algorithm (three iterations, 21 subsets), a 5-mm Gaussian filter, and a 70-cm FOV.

The CT transmission map is used for attenuation correction. Attenuation correction accounts for differences in activity due to location within the body (i.e., photons from deep sites are attenuated to a greater degree than photons from superficial sites). Attenuation-corrected and uncorrected PET scans, along with the CT and PET/CT scans, are reviewed on a workstation.

FDG, an analog of glucose, is distributed via the bloodstream after being glycolytically active tissues. Imaging is typically started at least 60 min after injection to allow sufficient blood pool clearance, thereby improving the target-to-background ratio. Normal physiologic uptake is seen in the brain and myocardium and, to a lesser extent, in the liver, spleen, bone marrow, gastrointestinal tract, testes, and skeletal muscles. Myocardial uptake is variable in fasting patients but often intense in nonfasting individuals. Skeletal muscle uptake is dependent on recent use of the muscle group. Activity within the blood pool, particularly in the mediastinum, can also be seen [13]. Other less frequent sites of uptake include the endometrium, breast, major and minor salivary glands, and brown fat in the supraclavicular and paraspinal regions [13–16]. Because FDG is excreted by the kidneys, intense activity is normally seen in the renal collecting system, ureters, and bladder [13] (Fig. 2).

Increased FDG uptake can also be seen in many benign processes. Increased uptake has been reported in healing fractures, granulomatous diseases, inflammatory/infectious processes, and foci of wound healing and repair such as ostomy sites [13] (Figs. 3, 4, and 5).

Currently, the initial investigations of ovarian masses include physical examination, biochemical analysis of tumor markers such as CA-125, and transvaginal ultrasound (TVUS). TVUS is the preferred imaging modality for initial evaluation because of its availability, high resolution, and lack of ionizing radiation. Using ultrasound, a wide range of sensitivities (87–100 %) and specificities (57–90 %) have been reported for detection of ovarian malignancies [19, 20, 25–27]. A systemic review revealed a sensitivity of 87 % and a specificity of 90 % for ultrasound combined with color Doppler in the diagnosis of ovarian cancer [28]. Magnetic resonance imaging (MRI) is often used for further characterization of indeterminate adnexal masses, with a sensitivity and specificity of 100 and 94 %, respectively [29]. Although MRI can be helpful in cancer detection, the major contribution of MRI in adnexal mass evaluation is its ability to provide a confident diagnosis in many common benign adnexal abnormalities [30].

The role of FDG-PET in the detection of primary ovarian cancer has been evaluated for almost two decades. Ovarian cancer is typically characterized by increased glucose metabolism and therefore demonstrates increased FDG uptake, whereas benign tumors are usually negative on PET imaging. Early studies were predominantly undertaken with 1st-generation whole-body PET scanners, which had a lower sensitivity and spatial resolution compared to the latest PET/CT technology. Nevertheless, results are still comparable to more recent reports using PET/CT. In 2000 and 2002, two studies assessing women with asymptomatic adnexal masses found FDG-PET to have a sensitivity of 58 % and specificity of 76–80 % [19, 25]. Similarly, two further studies evaluated FDG-PET for characterization of a suspicious pelvic mass and found sensitivities and specificities to range from 58 to 78 % and 78 to 87 %, respectively [26, 31]. Despite the relatively low sensitivity of FDG-PET in the detection of primary ovarian cancer, all of the false negative results were either small invasive stage I tumors or lesions of low malignant potential.

Data with fusion of anatomic and functional imaging using PET/CT resulted in more precise localization of suspicious areas of increased FDG uptake and enabled a better assessment of incidental ovarian findings. In 97 patients, FDG-PET/CT demonstrated areas of abnormally increased metabolic activity in 60 patients, whereas lesions were considered benign in 37 patients [32]. The sensitivity and specificity for FDG-PET/CT were 100 % (57/57) and 92.5 % (37/40), respectively. This was higher than all other imaging modalities including US, CT, MRI, and FDG-PEt alone. The group from Bologna found in 50 consecutive patients a sensitivity, specificity, and accuracy of 87, 100, and 92 %, respectively, compared with 90, 61, and 89 %, respectively, for TVUS. The authors concluded that FDG-PET/CT provides additional information to TVUS for differentiating benign from malignant pelvic lesions as well as to CT for the staging of ovarian cancer patients. These findings were further supported by a prospective study of 133 women with suspected ovarian cancer [24]. Histopathology showed benign tumors in 25 patients, borderline tumors in 13 patients, and malignant tumors in 95 patients. The accuracy of FDG-PET/CT (0.92) was higher compared to pelvic ultrasound (0.83) and contrast-enhanced CT or pelvic MRI (0.75; p = 0.013).

FDG-PET and FDG-PET/CT, however, do have certain limitations, which also need to be considered. FDG-PET is often not able to detect small tumor deposits (less than 5 mm in size) [20]. Ovarian cancer shows variable levels of increased FDG uptake depending on the cellular composition. Abdominal or pelvic masses containing large cystic components as well as mucinous tumors will often not be metabolically active. False negative results are also seen in borderline ovarian tumor and cystadenocarcinoma of the ovary [19, 31, 33]. In particular, differentiating benign from borderline ovarian tumors is often difficult on FDG-PET. Even though borderline ovarian tumors demonstrate low-grade malignancy, they can be associated with aggressive biologic behavior in the form of peritoneal deposits and lymphadenopathy. However, borderline ovarian tumors are often non-FDG avid or demonstrate low-grade FDG uptake due to their mucinous and serous cellular composition [32].

Although generally false-positive findings in the abdomen and pelvis are rare, early studies showed that in patients with pelvic masses a number of benign conditions can cause increased FDG uptake. These include benign cystadenomas, dermoid tumors, teratomas, schwannomas, endometriosis, and inflammatory process [19, 31, 33] (Fig. 9 – bilateral salpingitis). Increased FDG uptake in normal ovaries is found in premenopausal women; this is related to the time point of ovulation. Two studies reported increased FDG uptake in the ovary and uterine endometrium in the late follicular and early luteal phases of the menstrual cycle [34, 35].

In order to reduce errors in interpretation, specific emphasis needs to be directed towards a good technique when undertaking pelvic PET/CT imaging. Ideally, the bladder should be empty to avoid artifacts on PET images from a high concentration of radioactivity in the bladder. It is suggested that the patient is scanned in a caudal-to-cranial direction, thus imaging the pelvis at the beginning of the study. The CT portion of PET/CT is often helpful to identify bladder diverticula and focal retained activity in ureters. Pelvic imaging can be improved by intravenous injection of furosemide (20–40 mg) to reduce tracer retention in the urinary system. The CT portion of PET/CT is also helpful in identifying normal physiologic activity in bowel, endometrium, and blood vessels. Bowel preparation can be performed with oral hydration as well and some groups recommend the use of oral contrast [36]. The administration of butylscopolamine (20–40 mg) at the time FDG injection has been reported to reduce FDG uptake in the bowel [37].

The most important prognostic factor for ovarian cancer patients is the tumor stage: the 5-year survival rate is 93, 70, 37, and 25 % for stage I, stage II, stage III, and stage IV, respectively [38]. Ovarian cancer is typically staged by exploratory laparotomy at the time of primary debulking in accordance with the recommendations of the International Federation of Gynecology and Obstetrics (FIGO) [39]. Debulking surgery followed by adjuvant chemotherapy is considered the standard approach in newly diagnosed ovarian cancer. Studies have shown that when using platinum-based chemotherapy in patients with advanced ovarian disease, maximal cytoreduction, correlated to the minimal residual tumor mass after surgery, is one of the most powerful determinants of survival [40].

For preoperative staging of ovarian cancer, CT and MRI have been accepted as being the most useful imaging techniques. Studies evaluating performance of CT in preoperative staging of ovarian cancer have found sensitivities and specificities ranging from 72 to 82 % and 53 to 81 %, respectively [41, 42]. Recent studies have shown that, when used in conjunction with CT, FDG-PET is beneficial in evaluating distant metastases and equivocal lesions [20, 21, 42].

An initial study of 15 patients found that the addition of FDG-PET to CT improved the accuracy in preoperative staging of ovarian cancer from 53 to 87 % [42]. In a later study, 40 ovarian cancer patients underwent FDG-PET/CT with intravenous contrast-enhanced CT for staging prior to primary debulking surgery [21]. An increase in sensitivity, specificity, and accuracy was found for combined FDG-PET/CT compared to CT alone from 37.6 to 69.4 %, 97.1 to 97.5 %, and 89.7 to 94.0 %, respectively. FDG-PET/CT findings and the final pathological staging were in concordance in 75 % of cases.

More recent data has shown that using FDG-PET/CT can result in a stage migration in a significant number of patients. Out of 66 ovarian cancer patients, 64 were initially stage III and 2 were stage IV [43]. However, after PET/CT, 51 % (39/66) were restaged as stage III and 41 % (27/66) as stage IV (Fig. 10).