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Everything you need to know about Computed Tomography (CT) & CT Scanning

Positron Emission Tomography/Computed Tomography (PET/CT) in Ovarian Cancer

Harpreet K. Pannu, M.D., Robert Bristow, M.D., Frederick J. Montz, M.D., Richard L. Wahl, M.D., Elliot K. Fishman, M.D.


  • Accurate detection of metastatic disease is important for staging and surgically treating ovarian cancer
  • Peritoneal metastases are most common –
  • Can be difficult to detect on bowel/diaphragmatic/pelvic viscera surfaces by CT
  • Can be difficult to distinguish from physiologic uptake in abdomen/pelvis by PET
  • Combined morphologic and functional imaging may –
  • Increase sensitivity for detection of disease
  • Increase confidence in diagnosing lesions as malignant on CT
  • Improve specificity of PET by distinguishing pathologic from physiologic activity
  • Improve localization of pathologic activity on PET


Ovarian cancer

  • fifth most common malignancy in women
  • most common gynecologic malignancy to cause death
  • usually affects women over the age of 60 years.

Stage of disease

  • usually advanced (Stage III or IV) at presentation
  • Stage I: tumor limited to the ovaries
  • Stage II: extension into the pelvic tissues
  • Stage III: implants beyond the pelvis
  • Stage IV: distant or parenchymal liver metastases

Routes of spread

  • peritoneal fluid, lymphatics, and blood
  • peritoneal route is most common
  • common sites of implants are the pelvis, right hemidiaphragm, liver, right paracolic gutter, bowel and omentum
  • nodes involved are the iliac, retroperitoneal and inguinal nodes

Role of imaging

  • to determine extent of disease at presentation
  • to monitor for recurrence

Imaging of ovarian cancer:

Anatomic imaging

Computed tomography (CT)

  • overall sensitivity for peritoneal metastases 85-93%
  • sensitivity for subcentimeter lesions 25-50%
  • rapid study, easily available, well tolerated

Magnetic resonance (MR)

  • equivalent to CT for detecting peritoneal metastases
  • sensitivity 91% for detecting recurrent or residual disease

Metabolic imaging

Positron emission tomography (PET)

  • complementary test to CT/MR in patients with negative scans and rising tumor markers
  • variable sensitivities reported for detecting disease
  • subcentimeter lesions difficult to distinguish from bowel activity

Anatometabolic imaging


  • combined imaging has the potential to improve detection of metastases

Principles of FDG PET imaging:

  • Increased glucose (18FDG:fluorine-18-fluorodeoxyglucose) uptake by cancer cells
  • FDG trapped inside cancer cells – 18FDG phosphorylated but not metabolized further
  • Decay of 18FDG molecule (t1/2 =110 minutes) – positron emitted and annihilates by colliding with an electron – 2 photons emitted at 180 degrees from each other and detected by opposing detectors to form an image
  • High tumor to background ratio on image
  • Lesions greater than 5-10 mm detected with dedicated PET scanner

18FDG uptake by cancer cells

  • increased with viable cells and adequate tumor perfusion
  • increased with acute chemotherapy and radiation inflammation
  • decreased with necrosis
  • decreased after effective chemotherapy and chronic radiation change
  • decreased in hyperglycemia due to competing unlabeled glucose molecules

18FDG uptake by non-cancer cells

  • increased in inflammatory cells
  • increased in normal brain, heart, exercising skeletal muscle

Technology and advantages of PET/CT:

Both PET and CT gantries in same physical location

  • PET scan immediately follows CT scan
  • similar stomach/colon/bladder content on both scans for accurate fusion of abdominal images

Common table for both scans

  • patient position similar for both acquisitions
  • no significant shift internal organs/change in body curvature
  • no need for external markers/extensive computer fusion algorithms
  • calibration of imaging coordinates of both scanners

Automated intermodality registration

  • improved alignment of data to within few millimeters in 3 translation dimensions
  • improved alignment of data to within few degrees in 3 rotation dimensions
  • more precise anatomic localization
  • increased reader confidence in lesion diagnosis

Use of CT for transmission scan

  • decreased study time

Technique for PET/CT:

Patient preparation

  • fast 4 hours prior to scan – to lower insulin and blood sugar levels
  • avoid strenuous activity 1 day prior – to decrease skeletal muscle uptake
  • drink water for hydration – to enhance urinary excretion

Patient interview

  • recent surgery/biopsy – can increase uptake at surgical site
  • prior chemotherapy or radiation – can affect uptake
  • recent colony stimulating factors – can increase marrow uptake

Study technique

  • administer 750 mL ionic oral contrast 1 hour prior to imaging – to opacify bowel on CT
  • inject 10-15 mCi 18FDG intravenously 1 hour prior to imaging – injection 1 hour prior to scanning improves tumor to background ratio
  • patient voids prior to imaging – to decrease bladder activity
  • patient positioned supine on table with arms up
  • iodinated intravenous contrast not administered as it may adversely affect attenuation correction map from transmission CT scan
  • scans acquired from skull base to mid thigh level during quiet respiration
  • CT performed with 4.25 mm thick contiguous slices, --- mAs, 140 kVp
  • PET performed with 5-10 minute acquisition per imaging level

Interpretation of PET/CT images

Normal activity on PET

  • most common sites – brain, myocardium, bladder [7]
  • abdominal sites – liver, spleen, kidneys, bowel, stomach
  • other sites – marrow, tonsils, thyroid, breast

View larger image

Qualitative interpretation

  • most common method
  • workstation review of axial, coronal, sagittal images with varying gray scale, rotating views, and maximum intensity projection images [7]
  • review of CT, PET, and fused PET/CT images
  • qualitative determination of areas of pathologically increased uptake

Quantitative interpretation

  • calculation of standardized uptake value (SUV) of lesions [7]
  • SUV = [(mCi/mL in tissue) / mCi injected dose] X patient weight in gms
  • higher SUV (>3.25) suggestive of malignancy
  • rising SUV suggestive of tumor recurrence
  • SUV higher in obese patients and with smaller regions of interest (ROI)

Pelvic Disease

Figure 1
59 year old woman with recurrent ovarian cancer. (a) Increased activity right and left pelvis greater than surrounding bowel on PET. (b) Small nodules in sigmoid mesocolon on CT but no definite mass right pelvis. (c) Fused image shows activity in sigmoid nodules and over cecum. Tumor found at both sites at surgery.

C: view larger image
Figure 2
46 year old woman with recurrent ovarian cancer and elevated CA 125 to > 8000 U/mL. (a) Intense uptake in pelvis on PET. (b) Partially calcified masses on CT in left pelvis around bowel and superior to bladder. (c) Increased activity corresponds to pelvic masses compatible with tumor.

C: view larger image
Figure 3
46 year old woman with recurrent ovarian cancer. (a) Increased uptake in left pelvis on PET - bowel implant vs node. (b) Enlarged left iliac nodes on CT. (c) Activity in left iliac nodes on fused image and nodes were malignant at surgery. Misregistration of bladder activity in right pelvis.

C: view larger image

Abdominal Disease

Figure 4
46 year old woman with recurrent ovarian cancer and elevated CA 125 to > 8000 U/mL. (a) Uptake in right upper abdomen along liver surface on PET. (b) Calcified liver implant on CT. (c) Uptake corresponds to tumor mass on fused image.

C: view larger image
Figure 5
57 year old woman with recurrent ovarian cancer. (a) Curvilinear uptake in mass with cold center in right abdomen on PET. (b) Mass with cystic central and solid peripheral components on CT. (c) Solid areas demonstrate activity on fused image compatible with tumor.

C: view larger image

Chest Disease

Figure 6
59 year old with recurrent ovarian cancer. Increasing abdominal disease on CT and mediastinal adenopathy in setting of rising CA 125 likely due to metastatic disease. Increased uptake in enlarged nodes in the right paratracheal, bilateral hilar, subcarinal and prevascular regions on PET (a), CT (b), and fused (c) images.

C: view larger image

Increased sensitivity for detection of disease on fused images

Figure 7
55 year old woman with ovarian cancer and rising CA 125. (a) Minimal nodularity left paracolic gutter on CT suspicious for implants. (b) Linear slightly increased uptake in same area on PET. (c) Increased activity on PET corresponds to nodules on CT and is suggestive of tumor implants.

C: view larger image
Figure 8
59 year old woman with recurrent ovarian cancer. (a) No obvious mass adjacent to unopacified bowel on CT. (b) Small area of increased uptake midabdomen on PET. (c) Uptake localized to transverse colon on fused image. Tumor nodules involving transverse colon found at surgery.

C: view larger image
Figure 9
46 year old woman with recurrent ovarian cancer and elevated CA 125 to > 8000 U/mL. (a) Inhomogenous distribution of oral contrast on CT results in some small bowel loops being unopacified. (b) Uptake in mass in midabdomen on PET. (c) Fused image localizes mass and allows distinction of tumor from adjacent bowel loops.

C: view larger image

Distinguishing benign vs malignant lesions on CT

Figure 10
Pelvic recurrence vs postoperative collection. 75 year old woman with gross residual disease at second - look laparotomy 3 months prior to PET/CT. (a) Bilateral adnexal masses on CT. Mass on left is cystic and mass on right has near soft tissue attenuation. (b) Increased activity right pelvis on PET and photopenic area left pelvis. (c) Recurrent tumor right pelvis is hot on fused image and postoperative collection left pelvis shows no uptake.

C: view larger image

Distinguishing pathologic from physiologic activity on PET

Figure 11
73 year old woman with primary surgery for ovarian cancer 4 weeks prior to PET/CT. (a) Surgical incision path seen in abdominal wall on CT. Increased uptake in abdominal wall on PET corresponds to the scar on axial (b) and coronal (c) fused images. Increased activity is due to inflammatory change secondary to recent surgery.

C: view larger image


Figure 12
58 year old woman with recurrent ovarian cancer. (a) Cystic mass seen in left pelvis on CT. (b) Fused image shows activity right pelvis. (c) Inferior CT slice shows right pelvic activity is due to bladder. Activity seen on fused image in (b) is secondary to misregistration due to breathing. Left pelvic mass is a postoperative collection.

C: view larger image
Figure 13
57 year old woman with recurrent ovarian cancer. (a) Increased uptake in left abdomen on PET. (b) Small peritoneal implant in same area on CT. (c) Activity on fused image is over the stomach and just medial to actual location of implant. Misregistration is due to breathing.

C: view larger image

Normal Activity

Figure 14
Foci of increased activity appear larger on PET than actual size on CT. (a) Both ureters are normal in size on CT. (b) Increased activity in the ureters causes larger areas of uptake to appear on the PET image. (c) Fused image shows ureteric activity superimposed on the left psoas muscle.

C: view larger image


Anatometabolic imaging has the potential to improve the detection of metastatic ovarian cancer. Combined imaging can be used to diagnose disease with increased confidence on CT. Fusion of PET images with CT can improve localization of pathologic activity and distinction from physiologic uptake.


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© 1999-2020 Elliot K. Fishman, MD, FACR. All rights reserved.