DOI: 10.1148/rg.254045155
RadioGraphics 2005;25:1031-1043
© RSNA, 2005
Imaging of Pelvic Malignancies with In-Line FDG PET–CT: Case Examples and Common Pitfalls of FDG PET1
Naveen Subhas, MD,
Pavni V. Patel, MD,
Harpreet K. Pannu, MD,
Heather A. Jacene, MD,
Elliot K. Fishman, MD and
Richard L. Wahl, MD
1 From the Russell H. Morgan Department of Radiology & Radiological Science, Johns Hopkins University, 601 N Caroline St, Rm 3223, Baltimore, MD 21287-0817. Presented as an education exhibit at the 2003 RSNA Annual Meeting. Received August 3, 2004; revision requested October 25; final revision received January 21, 2005; accepted March 7. R.L.W. received honoraria from GE Medical Systems, Philips, Cardinal Health, and GSK; received grant support from GE Medical Systems; is a consultant of NMP and a consultant and stockholder of Threshold Pharmaceuticals; and holds licensed technology and patents from GSK. All other authors have no financial relationships to disclose.
Address correspondence to R.L.W. (e-mail: rwahl{at}jhmi.edu).
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Abstract
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The role of 2-[fluorine 18]fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET) in combination with computed tomography (CT) in the evaluation of pelvic malignancies has been rapidly growing in recent years. FDG PET has proved to be valuable in the evaluation of a variety of pelvic malignancies, including colorectal cancer, uterine cervical cancer, ovarian cancer, endometrial cancer, and non-Hodgkin lymphoma. However, a number of pitfalls are commonly encountered at FDG PET, including normal physiologic activity in bowel, ovaries, endometrium, and blood vessels and focal retained activity in ureters, bladder diverticula, pelvic kidneys, and urinary diversions. The use of an in-line FDG PET–CT system, with special attention given to proper patient preparation and scanning protocol, often provides valuable information to help localize and define disease and avoid potential diagnostic pitfalls.
© RSNA, 2005
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Introduction
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Positron emission tomography (PET) with 2-[fluorine 18]fluoro-2-deoxy-D-glucose (FDG) is increasingly being used in combination with computed tomography (CT) to evaluate abdominopelvic malignancies. In this article, we present our technique for PET-CT of the pelvis, with special emphasis on patient preparation and scanning protocol, and discuss normal FDG activity. We also discuss and illustrate the use of FDG PET and in-line PET-CT in the evaluation of various pelvic malignancies, including colorectal cancer, uterine cervical cancer, endometrial cancer, ovarian cancer, and non-Hodgkin lymphoma. In addition, we describe some common pitfalls of FDG PET caused by normal FDG activity and focal FDG retention and ways in which PET-CT can help avoid diagnostic errors in such cases.
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Technique for Pelvic PET-CT
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Proper patient preparation and scanning protocol are needed for optimal diagnostic accuracy. Considerations that are unique to in-line FDG PET–CT systems include bowel preparation techniques, reduction of FDG activity in the urinary bladder, and data 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 (1). At our institution, bowel-cleansing regimens are not used. 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. At our institution, this is typically accomplished by having the patient void completely immediately prior to the start of scanning and by imaging the pelvis early in the study. Occasionally, if there is concern for disease in a region of the renal pelvis that is not well seen due to urinary FDG activity, delayed postvoiding imaging (2–3-hour delay) with or without administration of a diuretic is used to decrease activity in excreted urine. Although only infrequently needed, bladder catheterization can be performed to reduce bladder activity, particularly in patients who cannot void well.
Metallic prostheses can cause foci of apparent increased FDG uptake due to attenuation correction (2). 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 data (2). At our institution, an ordered subset expectation maximum iterative reconstruction algorithm with two iterations and 28 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 of the pelvis is described in the following paragraphs and summarized in Table 1.
Patient Preparation
The patient is asked to take nothing by mouth for at least 4 hours 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 (eg, lymph node resection) to ensure proper distribution of radio-tracer. The patient’s blood glucose level 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, although no standardized level has been established in the literature. One hour prior to imaging, the FDG dose is injected and 900 mL of low-density barium (Readicat 1.3% weight/volume barium sulfate suspension; E-Z-EM, Westbury, 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. An additional 100 mL of oral contrast material is given approximately 30 minutes prior to imaging. Just prior to the start of scanning, the patient is asked to void completely to minimize bladder activity.
Scanning Protocol
For scanning, the patient is positioned supine and headfirst on an in-line 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 four-section multidetector Discovery LS PET/CT system (GE Medical Systems) is used with the following parameters: detector row configuration of 4 x 5 mm, 140 kVp, weight-adjusted milliamperage-seconds (mean, 80 mAs; range, 60–120 mAs), gantry rotation speed of 0.8 seconds per revolution, pitch of 6:1 (high-speed mode), and table feed of 22.5 mm/sec. A topogram is used to adjust the FOV so that it extends from the skull base to the midthigh level. The images are reconstructed on a 512 x 512 matrix with a 50-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. Five-minute emission acquisitions per FOV are obtained in two-dimensional mode. Thirty-five transverse PET scans are obtained per FOV, with a section thickness of 4.25 mm. Five to seven table positions are usually needed, with each position allowing coverage of 14.6 cm. The PET scans are reconstructed on a 128 x 128 matrix, with an ordered subset expectation maximum iterative reconstruction algorithm (two iterations, 28 subsets), an 8-mm Gaussian filter, and a 50-cm FOV.
The CT transmission map is used for attenuation correction. Attenuation correction accounts for differences in activity due to location within the body (ie, 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.
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Normal FDG Activity
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FDG, an analog of glucose, is distributed via the bloodstream after being intravenously injected and is taken up by glycolytically active tissues. Imaging is typically started at least 60 minutes 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 in question. Activity within the blood pool, particularly in the mediastinum, can also be seen (3). Other less frequent sites of uptake include the endometrium, breast, major and minor salivary glands, and brown fat in the supraclavicular and paraspinal regions (3–6). Because FDG is excreted by the kidneys, intense activity is normally seen in the renal collecting system, ureters, and bladder (3).
Increased FDG uptake can also be seen in many benign processes. Increased uptake has been reported in healing fractures, granulomatous diseases, inflammatory and degenerative joint diseases, infectious processes (including pneumonia, sinusitis, and abscess), inflammatory processes such as pancreatitis, and foci of wound healing and repair such as ostomy sites (3).
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FDG PET and In-Line FDG PET–CT in Pelvic Malignancies
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The usefulness of FDG PET in evaluating pelvic malignancies has been well established (7). FDG PET has been shown to be very sensitive and specific in many pelvic malignancies, including colorectal cancer, uterine cervical and endometrial cancer, ovarian cancer, and non-Hodgkin lymphoma (Table 2). However, the usefulness of FDG PET in urothelial and prostate cancer is limited due to specific challenges. In urothelial malignancies, intense radiotracer activity in excreted urine is a major pitfall, whereas in prostate cancer, poor sensitivity for osseous metastases is a significant drawback (8,9). These two malignancies will not be discussed further in this article. In recent years, with the advent of dedicated in-line PET-CT systems, combined FDG PET–CT has begun rapidly replacing FDG PET alone in the evaluation of pelvic tumors (10). Moreover, evidence to support the usefulness of combined FDG PET–CT in further applications is rapidly emerging.
Numerous studies have shown FDG PET to be useful in the detection of colorectal cancer. A meta-analysis of 11 studies showed that FDG PET had an overall sensitivity and specificity of 97% and 76%, respectively, in detecting recurrent colorectal carcinoma (11). Comparison of FDG PET with CT has shown FDG PET to be more accurate than pelvic CT (95% vs 65%) in detecting local disease in recurrent colorectal cancer (12). A recent study directly comparing in-line FDG PET–CT with FDG PET alone showed that the former allows greater accuracy in the staging of colorectal cancer (89% vs 78%) and allows a greater number of lesions to be characterized as definitely normal or abnormal, thereby decreasing the number of equivocal and probable lesions (Fig 1) (13).
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Figure 1a. Primary rectal carcinoma with lymph node metastasis. (a) FDG PET scan shows metabolically active foci in the rectum and right inguinal region. (b) CT scan shows an enlarged right inguinal lymph node (arrow) and a normal-appearing rectum. (c) PET-CT scan shows increased uptake localized to the enlarged right inguinal lymph node and rectum, findings that confirm rectal carcinoma with lymph node metastasis.
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Figure 1b. Primary rectal carcinoma with lymph node metastasis. (a) FDG PET scan shows metabolically active foci in the rectum and right inguinal region. (b) CT scan shows an enlarged right inguinal lymph node (arrow) and a normal-appearing rectum. (c) PET-CT scan shows increased uptake localized to the enlarged right inguinal lymph node and rectum, findings that confirm rectal carcinoma with lymph node metastasis.
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Figure 1c. Primary rectal carcinoma with lymph node metastasis. (a) FDG PET scan shows metabolically active foci in the rectum and right inguinal region. (b) CT scan shows an enlarged right inguinal lymph node (arrow) and a normal-appearing rectum. (c) PET-CT scan shows increased uptake localized to the enlarged right inguinal lymph node and rectum, findings that confirm rectal carcinoma with lymph node metastasis.
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In uterine cervical cancer, FDG PET has been shown to be effective in disease staging, detection of early recurrence, and determining prognosis. The sensitivity and specificity of FDG PET in detecting local and distant disease have been reported as excellent in both initial staging (100% sensitivity and specificity) and restaging (82% and 100% sensitivity and 97% and 90% specificity for local and distant disease, respectively) (14). In detecting early recurrence, FDG PET has demonstrated a sensitivity of 90% and a specificity of 76% (15). Another recent study showed that persistent or new uptake of FDG in patients with uterine cervical cancer who had undergone radiation therapy and chemotherapy was the most significant factor for predicting metastasis of and death from uterine cervical cancer (16). FDG PET has also been shown to be more sensitive than magnetic resonance (MR) imaging or CT in detecting paraaortic lymph node metastases from advanced uterine cervical cancer (17, 18). Although to our knowledge no studies on the use of in-line FDG PET–CT in uterine cervical cancer have been published, this modality seems promising in reducing the frequency of occurrence of some common false-positive results (eg, focal rectal and ureteral activity) and false-negative results (eg, disease in the perivesicular region) that have been reported in studies using FDG PET alone (Fig 2) (14,15).
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Figure 2a. Advanced cervical cancer. (a) FDG PET scan shows metabolically active foci in the pelvis above the bladder (B), along the paraaortic and iliac regions, and in the left supraclavicular region. (b, c) On CT (b) and PET-CT (c) scans, the foci in a are localized to the cervix and lymph nodes (arrowheads in b), findings that confirm advanced cervical cancer. B = bladder.
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Figure 2b. Advanced cervical cancer. (a) FDG PET scan shows metabolically active foci in the pelvis above the bladder (B), along the paraaortic and iliac regions, and in the left supraclavicular region. (b, c) On CT (b) and PET-CT (c) scans, the foci in a are localized to the cervix and lymph nodes (arrowheads in b), findings that confirm advanced cervical cancer. B = bladder.
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Figure 2c. Advanced cervical cancer. (a) FDG PET scan shows metabolically active foci in the pelvis above the bladder (B), along the paraaortic and iliac regions, and in the left supraclavicular region. (b, c) On CT (b) and PET-CT (c) scans, the foci in a are localized to the cervix and lymph nodes (arrowheads in b), findings that confirm advanced cervical cancer. B = bladder.
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FDG PET has shown similar results in detecting recurrence in patients who have undergone therapy for endometrial carcinoma, with sensitivities and specificities of 96%–100% and 78%–88%, respectively (19,20). Although to our knowledge no studies of the use of in-line FDG PET–CT in endometrial carcinoma have been conducted, FDG PET in conjunction with anatomic imaging (CT–MR imaging) has been reported to be more sensitive, specific, and accurate than CT–MR imaging alone (Fig 3) (20).
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Figure 3a. Recurrent endometrial carcinoma after hysterectomy. B = bladder. (a) FDG PET scan demonstrates metabolically active foci in the left obturator region and in the paraaortic regions. (b) CT scan shows enlarged lymph nodes (arrowheads) that correspond to the foci in a. (c) PET-CT scan shows areas of increased uptake localized to the enlarged lymph nodes, findings that confirm metastatic disease. Normal physiologic uptake is seen in the bladder.
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Figure 3b. Recurrent endometrial carcinoma after hysterectomy. B = bladder. (a) FDG PET scan demonstrates metabolically active foci in the left obturator region and in the paraaortic regions. (b) CT scan shows enlarged lymph nodes (arrowheads) that correspond to the foci in a. (c) PET-CT scan shows areas of increased uptake localized to the enlarged lymph nodes, findings that confirm metastatic disease. Normal physiologic uptake is seen in the bladder.
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Figure 3c. Recurrent endometrial carcinoma after hysterectomy. B = bladder. (a) FDG PET scan demonstrates metabolically active foci in the left obturator region and in the paraaortic regions. (b) CT scan shows enlarged lymph nodes (arrowheads) that correspond to the foci in a. (c) PET-CT scan shows areas of increased uptake localized to the enlarged lymph nodes, findings that confirm metastatic disease. Normal physiologic uptake is seen in the bladder.
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Mixed results have been reported with respect to the value of FDG PET in evaluating ovarian cancer. The sensitivity and specificity of FDG PET in the detection of recurrent disease have ranged from 45% to 100% and from 40% to 99%, respectively (21–24). Direct comparison of FDG PET with CT has also yielded mixed results. Several studies have shown FDG PET to be more sensitive and accurate than CT in detecting recurrent disease, whereas others have reported no difference between the two modalities or even a higher sensitivity for CT, especially for smaller (3–7-mm) lesions (21,22,25). The data regarding combined FDG PET–CT in the evaluation of ovarian malignancy are still emerging. In a recent study of preoperative tumor staging, CT alone had an accuracy of 53%, whereas FDG PET evaluated in conjunction with CT had an accuracy of 87% (26). Two other recent studies conducted with an in-line FDG PET–CT system have been published. The first study reported an 82% sensitivity, an 83% specificity, and a 94% positive predictive value for detecting recurrent disease (lesions 
1 cm), whereas the second study showed only moderate sensitivity (72%) for detecting recurrent disease, with 100% sensitivity for malignant adenopathy but a much lower sensitivity for peritoneal lesions (13% for lesions 
1 cm and 50% for lesions >1 cm) (23,24). Similar low sensitivities for detecting peritoneal disease (57%–66%) have been reported by other authors (25,27). On the basis of these studies, it appears that very small lesions (<5 mm) in ovarian cancer can commonly escape detection at FDG PET and FDG PET–CT (Fig 4).
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Figure 4a. Recurrent ovarian carcinoma with peritoneal metastases. (a) FDG PET scan shows metabolically active foci in the anterior abdomen near bowel loops (arrowheads). (b) CT scan demonstrates soft-tissue implants (arrowheads) that correspond to the foci in a. (c) PET-CT scan shows areas of increased uptake localized to the soft-tissue implants (arrowheads), findings that confirm metastatic disease.
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Figure 4b. Recurrent ovarian carcinoma with peritoneal metastases. (a) FDG PET scan shows metabolically active foci in the anterior abdomen near bowel loops (arrowheads). (b) CT scan demonstrates soft-tissue implants (arrowheads) that correspond to the foci in a. (c) PET-CT scan shows areas of increased uptake localized to the soft-tissue implants (arrowheads), findings that confirm metastatic disease.
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Figure 4c. Recurrent ovarian carcinoma with peritoneal metastases. (a) FDG PET scan shows metabolically active foci in the anterior abdomen near bowel loops (arrowheads). (b) CT scan demonstrates soft-tissue implants (arrowheads) that correspond to the foci in a. (c) PET-CT scan shows areas of increased uptake localized to the soft-tissue implants (arrowheads), findings that confirm metastatic disease.
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A common systemic malignancy that involves the pelvis is non-Hodgkin lymphoma. A number of studies have shown FDG PET to be useful and, in fact, superior to CT for primary staging and evaluating disease extent in both Hodgkin disease and non-Hodgkin lymphoma, with sensitivities of 82%–99% and specificities of 99%–100% (28). Limitations of FDG PET in lymphoma have included variable FDG uptake in low-grade lymphoma; physiologic activity in muscles, bone marrow, bowel, and the urinary system; and FDG uptake in inflammatory or infectious processes, any of which may mask or mimic tumor (29). Although data regarding the use of in-line FDG PET–CT systems in evaluating lymphoma are sparse, preliminary results appear to indicate promise in helping reduce such limitations and more effectively guide biopsy when indicated (Fig 5) (30).
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Figure 5a. Mesenteric metastasis in a patient with lymphoma (reticulum cell sarcoma) of the right iliopsoas muscle. B = bladder, K = left kidney. (a) Coronal FDG PET scan demonstrates metabolically active foci in the right lower quadrant near bowel loops. (b) Axial FDG PET scan demonstrates metabolically active foci in the left midabdomen, also near bowel loops. (c) Coronal CT scan shows a soft-tissue-attenuation nodule in the right lower quadrant (arrowhead). The nodule is adjacent to a loop of small bowel that is enhanced with oral contrast material. (d) Axial CT scan shows nodularity (arrowhead) adjacent to the descending colon. (e, f) On coronal (e) and axial (f) PET-CT scans, the metabolically active foci are localized to the areas of interest in a–d. Normal physiologic FDG activity is seen in the inferior pole of the left kidney and the bladder on all six scans. These findings confirm that the areas of increased activity are not due to physiologic FDG uptake within bowel, but in fact represent mesenteric metastases adjacent to bowel loops.
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Figure 5b. Mesenteric metastasis in a patient with lymphoma (reticulum cell sarcoma) of the right iliopsoas muscle. B = bladder, K = left kidney. (a) Coronal FDG PET scan demonstrates metabolically active foci in the right lower quadrant near bowel loops. (b) Axial FDG PET scan demonstrates metabolically active foci in the left midabdomen, also near bowel loops. (c) Coronal CT scan shows a soft-tissue-attenuation nodule in the right lower quadrant (arrowhead). The nodule is adjacent to a loop of small bowel that is enhanced with oral contrast material. (d) Axial CT scan shows nodularity (arrowhead) adjacent to the descending colon. (e, f) On coronal (e) and axial (f) PET-CT scans, the metabolically active foci are localized to the areas of interest in a–d. Normal physiologic FDG activity is seen in the inferior pole of the left kidney and the bladder on all six scans. These findings confirm that the areas of increased activity are not due to physiologic FDG uptake within bowel, but in fact represent mesenteric metastases adjacent to bowel loops.
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Figure 5c. Mesenteric metastasis in a patient with lymphoma (reticulum cell sarcoma) of the right iliopsoas muscle. B = bladder, K = left kidney. (a) Coronal FDG PET scan demonstrates metabolically active foci in the right lower quadrant near bowel loops. (b) Axial FDG PET scan demonstrates metabolically active foci in the left midabdomen, also near bowel loops. (c) Coronal CT scan shows a soft-tissue-attenuation nodule in the right lower quadrant (arrowhead). The nodule is adjacent to a loop of small bowel that is enhanced with oral contrast material. (d) Axial CT scan shows nodularity (arrowhead) adjacent to the descending colon. (e, f) On coronal (e) and axial (f) PET-CT scans, the metabolically active foci are localized to the areas of interest in a–d. Normal physiologic FDG activity is seen in the inferior pole of the left kidney and the bladder on all six scans. These findings confirm that the areas of increased activity are not due to physiologic FDG uptake within bowel, but in fact represent mesenteric metastases adjacent to bowel loops.
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Figure 5d. Mesenteric metastasis in a patient with lymphoma (reticulum cell sarcoma) of the right iliopsoas muscle. B = bladder, K = left kidney. (a) Coronal FDG PET scan demonstrates metabolically active foci in the right lower quadrant near bowel loops. (b) Axial FDG PET scan demonstrates metabolically active foci in the left midabdomen, also near bowel loops. (c) Coronal CT scan shows a soft-tissue-attenuation nodule in the right lower quadrant (arrowhead). The nodule is adjacent to a loop of small bowel that is enhanced with oral contrast material. (d) Axial CT scan shows nodularity (arrowhead) adjacent to the descending colon. (e, f) On coronal (e) and axial (f) PET-CT scans, the metabolically active foci are localized to the areas of interest in a–d. Normal physiologic FDG activity is seen in the inferior pole of the left kidney and the bladder on all six scans. These findings confirm that the areas of increased activity are not due to physiologic FDG uptake within bowel, but in fact represent mesenteric metastases adjacent to bowel loops.
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Figure 5e. Mesenteric metastasis in a patient with lymphoma (reticulum cell sarcoma) of the right iliopsoas muscle. B = bladder, K = left kidney. (a) Coronal FDG PET scan demonstrates metabolically active foci in the right lower quadrant near bowel loops. (b) Axial FDG PET scan demonstrates metabolically active foci in the left midabdomen, also near bowel loops. (c) Coronal CT scan shows a soft-tissue-attenuation nodule in the right lower quadrant (arrowhead). The nodule is adjacent to a loop of small bowel that is enhanced with oral contrast material. (d) Axial CT scan shows nodularity (arrowhead) adjacent to the descending colon. (e, f) On coronal (e) and axial (f) PET-CT scans, the metabolically active foci are localized to the areas of interest in a–d. Normal physiologic FDG activity is seen in the inferior pole of the left kidney and the bladder on all six scans. These findings confirm that the areas of increased activity are not due to physiologic FDG uptake within bowel, but in fact represent mesenteric metastases adjacent to bowel loops.
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Figure 5f. Mesenteric metastasis in a patient with lymphoma (reticulum cell sarcoma) of the right iliopsoas muscle. B = bladder, K = left kidney. (a) Coronal FDG PET scan demonstrates metabolically active foci in the right lower quadrant near bowel loops. (b) Axial FDG PET scan demonstrates metabolically active foci in the left midabdomen, also near bowel loops. (c) Coronal CT scan shows a soft-tissue-attenuation nodule in the right lower quadrant (arrowhead). The nodule is adjacent to a loop of small bowel that is enhanced with oral contrast material. (d) Axial CT scan shows nodularity (arrowhead) adjacent to the descending colon. (e, f) On coronal (e) and axial (f) PET-CT scans, the metabolically active foci are localized to the areas of interest in a–d. Normal physiologic FDG activity is seen in the inferior pole of the left kidney and the bladder on all six scans. These findings confirm that the areas of increased activity are not due to physiologic FDG uptake within bowel, but in fact represent mesenteric metastases adjacent to bowel loops.
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Common Pitfalls of Pelvic FDG PET
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Despite the high sensitivity of FDG PET in these pelvic malignancies, one of the inherent pitfalls of metabolic imaging has been the relatively low specificity with false-positive results due to increased FDG uptake in normal organs, inflammatory conditions, and benign processes, findings that can complicate image assessment Table 3) (31). Increased uptake at FDG PET has been reported in many benign pelvic processes, including uterine fibroids, endometriosis, and even the normal menstrual cycle (3,31,32). Inflammatory changes from recent surgery and radiation therapy have also demonstrated increased FDG uptake (33,34). In addition, increased FDG uptake has been reported in sacral fractures (35). Focal physiologic radiotracer activity in bowel loops, the urinary system, the uterus, bone marrow, and skeletal muscle can similarly lead to false-positive interpretations (3,32,36). Figures 6–8 demonstrate physiologic FDG activity in bowel loops, ovary and uterus, and blood vessels, respectively, findings that were confirmed at FDG PET–CT. Figures 9–12 demonstrate focal urinary retention of FDG in a ureter, bladder diverticulum, pelvic kidney, and surgically constructed ileal conduit, respectively, findings that are readily recognized at FDG PET–CT. Figure 13 demonstrates a false-negative result due to urinary FDG activity in the bladder at FDG PET of the perivesicular area. This finding was recognized as being a false-negative result upon examination of the CT and FDG PET–CT scans. The use of CT for attenuation correction for in-line PET-CT systems produces unique artifacts, two of which are important in imaging of the pelvis. The first artifact, which was discussed earlier, is foci of apparent increased FDG uptake around metallic prostheses such as hip replacements; this artifact can be reduced by minimizing patient motion, using iterative reconstruction of CT data, and examining non-attenuation-corrected images (2). The second artifact is misregistration of soft-tissue or fluid attenuation within the bowel due to gut motion between the FDG PET and CT scans, resulting in artifactual foci of increased or decreased uptake near the bowel on the PET scans (37). Careful correlation with the anatomic data from the CT and PET-CT scans is helpful in recognizing this pitfall (Fig 14).
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Figure 6a. Physiologic FDG activity in blood vessels. R = rectum. (a) FDG PET scan shows bilateral foci of increased activity in the region of the femoral vessels (arrowheads), with greater involvement on the right side than on the left. (b) CT scan shows normal iliac vessels (arrowheads) with no pathologic process. (c) On a PET-CT scan, the foci of increased activity are localized to the iliac veins (arrows), findings that are compatible with normal physiologic FDG uptake in blood vessels. Normal physiologic activity is seen in the rectum on all three scans.
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Figure 6b. Physiologic FDG activity in blood vessels. R = rectum. (a) FDG PET scan shows bilateral foci of increased activity in the region of the femoral vessels (arrowheads), with greater involvement on the right side than on the left. (b) CT scan shows normal iliac vessels (arrowheads) with no pathologic process. (c) On a PET-CT scan, the foci of increased activity are localized to the iliac veins (arrows), findings that are compatible with normal physiologic FDG uptake in blood vessels. Normal physiologic activity is seen in the rectum on all three scans.
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Figure 6c. Physiologic FDG activity in blood vessels. R = rectum. (a) FDG PET scan shows bilateral foci of increased activity in the region of the femoral vessels (arrowheads), with greater involvement on the right side than on the left. (b) CT scan shows normal iliac vessels (arrowheads) with no pathologic process. (c) On a PET-CT scan, the foci of increased activity are localized to the iliac veins (arrows), findings that are compatible with normal physiologic FDG uptake in blood vessels. Normal physiologic activity is seen in the rectum on all three scans.
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Figure 7a. Physiologic FDG activity in bowel loops in a patient with a history of endometrial cancer. (a) FDG PET scan shows multiple foci of increased FDG activity in the right midanterior portion of the abdomen. (b) CT scan obtained at the same level demonstrates normal-appearing bowel loops containing oral contrast material. No abnormal soft-tissue nodules are seen. (c) On a PET-CT scan, the foci of increased activity are localized to bowel loops, findings that confirm normal physiologic FDG uptake (cf Figs 4, 5).
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Figure 7b. Physiologic FDG activity in bowel loops in a patient with a history of endometrial cancer. (a) FDG PET scan shows multiple foci of increased FDG activity in the right midanterior portion of the abdomen. (b) CT scan obtained at the same level demonstrates normal-appearing bowel loops containing oral contrast material. No abnormal soft-tissue nodules are seen. (c) On a PET-CT scan, the foci of increased activity are localized to bowel loops, findings that confirm normal physiologic FDG uptake (cf Figs 4, 5).
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Figure 7c. Physiologic FDG activity in bowel loops in a patient with a history of endometrial cancer. (a) FDG PET scan shows multiple foci of increased FDG activity in the right midanterior portion of the abdomen. (b) CT scan obtained at the same level demonstrates normal-appearing bowel loops containing oral contrast material. No abnormal soft-tissue nodules are seen. (c) On a PET-CT scan, the foci of increased activity are localized to bowel loops, findings that confirm normal physiologic FDG uptake (cf Figs 4, 5).
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Figure 8a. Physiologic FDG activity in the ovary and uterus in an 18-year-old woman with Hodgkin lymphoma. (a) FDG PET scan shows two foci of increased activity in the pelvis. (b) CT scan depicts a right ovarian cyst (O) and a portion of the uterus (U). (c) PET-CT scan shows two foci of increased activity localized to the right ovary and the uterus, findings that are compatible with normal physiologic FDG uptake in a functional ovarian cyst and the endometrium.
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Figure 8b. Physiologic FDG activity in the ovary and uterus in an 18-year-old woman with Hodgkin lymphoma. (a) FDG PET scan shows two foci of increased activity in the pelvis. (b) CT scan depicts a right ovarian cyst (O) and a portion of the uterus (U). (c) PET-CT scan shows two foci of increased activity localized to the right ovary and the uterus, findings that are compatible with normal physiologic FDG uptake in a functional ovarian cyst and the endometrium.
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Figure 8c. Physiologic FDG activity in the ovary and uterus in an 18-year-old woman with Hodgkin lymphoma. (a) FDG PET scan shows two foci of increased activity in the pelvis. (b) CT scan depicts a right ovarian cyst (O) and a portion of the uterus (U). (c) PET-CT scan shows two foci of increased activity localized to the right ovary and the uterus, findings that are compatible with normal physiologic FDG uptake in a functional ovarian cyst and the endometrium.
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Figure 9a. Focal retention of FDG in a ureter. (a, b) Coronal (a) and axial (b) FDG PET scans show a focus of increased activity in the right side of the retroperitoneum. The coronal scan shows normal physiologic activity in the bladder (B). (c) CT scan shows no abnormally enlarged lymph nodes or soft-tissue masses. A normal right ureter is seen (arrowhead). (d) PET-CT scan shows increased radiotracer uptake localized to the right ureter, a finding that confirms focal retention of FDG in the ureter.
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Figure 9b. Focal retention of FDG in a ureter. (a, b) Coronal (a) and axial (b) FDG PET scans show a focus of increased activity in the right side of the retroperitoneum. The coronal scan shows normal physiologic activity in the bladder (B). (c) CT scan shows no abnormally enlarged lymph nodes or soft-tissue masses. A normal right ureter is seen (arrowhead). (d) PET-CT scan shows increased radiotracer uptake localized to the right ureter, a finding that confirms focal retention of FDG in the ureter.
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Figure 9c. Focal retention of FDG in a ureter. (a, b) Coronal (a) and axial (b) FDG PET scans show a focus of increased activity in the right side of the retroperitoneum. The coronal scan shows normal physiologic activity in the bladder (B). (c) CT scan shows no abnormally enlarged lymph nodes or soft-tissue masses. A normal right ureter is seen (arrowhead). (d) PET-CT scan shows increased radiotracer uptake localized to the right ureter, a finding that confirms focal retention of FDG in the ureter.
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Figure 9d. Focal retention of FDG in a ureter. (a, b) Coronal (a) and axial (b) FDG PET scans show a focus of increased activity in the right side of the retroperitoneum. The coronal scan shows normal physiologic activity in the bladder (B). (c) CT scan shows no abnormally enlarged lymph nodes or soft-tissue masses. A normal right ureter is seen (arrowhead). (d) PET-CT scan shows increased radiotracer uptake localized to the right ureter, a finding that confirms focal retention of FDG in the ureter.
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Figure 10a. Focal retention of FDG in a bladder diverticulum. B = bladder. (a) PET scan shows increased FDG activity (arrowhead) just posterior to and to the left of the bladder. (b) CT scan demonstrates a bladder diverticulum (arrowhead). (c) PET-CT scan shows increased radiotracer activity localized to the bladder diverticulum (arrowhead), a finding that confirms focal retention of FDG in the diverticulum.
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Figure 10b. Focal retention of FDG in a bladder diverticulum. B = bladder. (a) PET scan shows increased FDG activity (arrowhead) just posterior to and to the left of the bladder. (b) CT scan demonstrates a bladder diverticulum (arrowhead). (c) PET-CT scan shows increased radiotracer activity localized to the bladder diverticulum (arrowhead), a finding that confirms focal retention of FDG in the diverticulum.
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Figure 10c. Focal retention of FDG in a bladder diverticulum. B = bladder. (a) PET scan shows increased FDG activity (arrowhead) just posterior to and to the left of the bladder. (b) CT scan demonstrates a bladder diverticulum (arrowhead). (c) PET-CT scan shows increased radiotracer activity localized to the bladder diverticulum (arrowhead), a finding that confirms focal retention of FDG in the diverticulum.
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Figure 11a. Focal retention of FDG in a pelvic kidney. B = bladder. (a) FDG PET scan shows a focus of increased activity in the left side of the pelvis (arrowhead). Arrows indicate areas of normal physiologic FDG uptake in the right ureter. Normal uptake is also seen in the bladder. (b) CT scan shows a pelvic kidney (K). (c) On a PET-CT scan, the focus of increased activity in the left side of the pelvis is localized to the pelvic kidney (arrowhead), a finding that is compatible with focal retention of FDG in the collecting system of the pelvic kidney. Again, note the areas of normal physiologic FDG uptake in the right ureter (arrows) and bladder.
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Figure 11b. Focal retention of FDG in a pelvic kidney. B = bladder. (a) FDG PET scan shows a focus of increased activity in the left side of the pelvis (arrowhead). Arrows indicate areas of normal physiologic FDG uptake in the right ureter. Normal uptake is also seen in the bladder. (b) CT scan shows a pelvic kidney (K). (c) On a PET-CT scan, the focus of increased activity in the left side of the pelvis is localized to the pelvic kidney (arrowhead), a finding that is compatible with focal retention of FDG in the collecting system of the pelvic kidney. Again, note the areas of normal physiologic FDG uptake in the right ureter (arrows) and bladder.
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Figure 11c. Focal retention of FDG in a pelvic kidney. B = bladder. (a) FDG PET scan shows a focus of increased activity in the left side of the pelvis (arrowhead). Arrows indicate areas of normal physiologic FDG uptake in the right ureter. Normal uptake is also seen in the bladder. (b) CT scan shows a pelvic kidney (K). (c) On a PET-CT scan, the focus of increased activity in the left side of the pelvis is localized to the pelvic kidney (arrowhead), a finding that is compatible with focal retention of FDG in the collecting system of the pelvic kidney. Again, note the areas of normal physiologic FDG uptake in the right ureter (arrows) and bladder.
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Figure 12a. Focal retention of FDG in an ileal conduit. B = bowel. (a) FDG PET scan shows an intense focus of increased FDG activity in the right lower abdomen (arrowhead). There is normal physiologic activity in the bowel and an accumulation of excreted FDG in an ostomy bag (O). (b) CT scan demonstrates a focal fluid collection (arrowhead), a finding that is compatible with an ileal conduit. No pathologic process is noted. (c) On a PET-CT scan, the focus of increased activity is localized to the ileal conduit (arrowhead), a finding that is compatible with focal retention of FDG in the ileal conduit. Again, note the normal physiologic activity in the bowel and the accumulation of excreted FDG in the ostomy bag (O).
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Figure 12b. Focal retention of FDG in an ileal conduit. B = bowel. (a) FDG PET scan shows an intense focus of increased FDG activity in the right lower abdomen (arrowhead). There is normal physiologic activity in the bowel and an accumulation of excreted FDG in an ostomy bag (O). (b) CT scan demonstrates a focal fluid collection (arrowhead), a finding that is compatible with an ileal conduit. No pathologic process is noted. (c) On a PET-CT scan, the focus of increased activity is localized to the ileal conduit (arrowhead), a finding that is compatible with focal retention of FDG in the ileal conduit. Again, note the normal physiologic activity in the bowel and the accumulation of excreted FDG in the ostomy bag (O).
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Figure 12c. Focal retention of FDG in an ileal conduit. B = bowel. (a) FDG PET scan shows an intense focus of increased FDG activity in the right lower abdomen (arrowhead). There is normal physiologic activity in the bowel and an accumulation of excreted FDG in an ostomy bag (O). (b) CT scan demonstrates a focal fluid collection (arrowhead), a finding that is compatible with an ileal conduit. No pathologic process is noted. (c) On a PET-CT scan, the focus of increased activity is localized to the ileal conduit (arrowhead), a finding that is compatible with focal retention of FDG in the ileal conduit. Again, note the normal physiologic activity in the bowel and the accumulation of excreted FDG in the ostomy bag (O).
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Figure 13a. False-negative result due to FDG activity in the bladder in a patient with recurrent ovarian cancer. (a) CT scan demonstrates minimal nodularity near the bladder dome (Tumor), a finding that proved to be metastatic disease at surgery. (b, c) FDG PET (b) and PET-CT (c) scans fail to show increased metabolic activity in the tumor nodule due to accumulation of excreted FDG in the bladder (B). There is also a focus of increased metabolic activity in an enlarged right inguinal node, a finding that is compatible with metastasis.
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Figure 13b. False-negative result due to FDG activity in the bladder in a patient with recurrent ovarian cancer. (a) CT scan demonstrates minimal nodularity near the bladder dome (Tumor), a finding that proved to be metastatic disease at surgery. (b, c) FDG PET (b) and PET-CT (c) scans fail to show increased metabolic activity in the tumor nodule due to accumulation of excreted FDG in the bladder (B). There is also a focus of increased metabolic activity in an enlarged right inguinal node, a finding that is compatible with metastasis.
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Figure 13c. False-negative result due to FDG activity in the bladder in a patient with recurrent ovarian cancer. (a) CT scan demonstrates minimal nodularity near the bladder dome (Tumor), a finding that proved to be metastatic disease at surgery. (b, c) FDG PET (b) and PET-CT (c) scans fail to show increased metabolic activity in the tumor nodule due to accumulation of excreted FDG in the bladder (B). There is also a focus of increased metabolic activity in an enlarged right inguinal node, a finding that is compatible with metastasis.
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Figure 14a. Apparent increased FDG activity (attenuation correction artifact) around hip replacements (H). B = bladder. (a) CT scan shows artifact from bilateral hip replacements. (b, c) Attenuation-corrected PET (b) and PET-CT (c) scans show apparent increased FDG activity (arrowheads) around the hip replacements. (d) Non-attenuation-corrected PET scan shows no increased activity, a finding that confirms that the "increased activity" on the attenuation-corrected image is due to reconstruction artifact. Normal physiologic FDG accumulation is seen in the bladder on all four scans.
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Abstract
Introduction
