George Segall, M.D.

VA Palo AltoHealth Care System

Stanford University

Problems and Pitfalls in the Interpretation of PET/CT

False Negative FDG PET

Histology

Size

Post prandial scans

Hyperglycemia

Low-grade gliomaLow-grade lymphomaBronchoalveolar lung cancerHepatomaRenal cell carcinomaProstate cancer

< 10 mm

> 150 mg/dL

57 year old man with stage IV left tonsillar scca treated with chemoradiation 21 months ago. Patient was lost to follow-up until he was referred for PET/CT. Coronal images show low FDG uptake in the brain, and high uptake in the heart and skeletal muscles.

Post Prandial Scan

• Fasting:

Euglycemia 6 hours

Diabetes12 hours

fed 04/25 fasting 05/08

Post Prandial Scan

51 year old man with colon polyps and a stricture referred for PET/CT to evaluate for possible malignancy. Fasting blood glucose level = 289 mg/dL. Coronal images show a good quality scan with normal FDG biodistribution.

Fasting Scan in a Diabetic

69 year old man with 2.3 cm RUL NSC lung cancer. FBS = 309 mg/dL. No insulin was given. Coronal images show a good quality scan with high FDG tumor uptake (max SUV 5.4)

Hyperglycemia

63 year old man with 5 cm RUL adenocarcinoma. FBS = 299 mg/dL; 90 minutes after 15u of reg insulin IV FBS = 179 mg/dL at which time FDG was injected. Coronal images show a “muscle scan” with faint tumor uptake (max SUV = 2.0)

Insulin Effect on FDG uptake

False Positive FDG PET

Physiologic

Benign Neoplasm

Inflammatory

Miscellaneous

Adenoma

Granuloma, sarcoid, rheumatoid

Prosthesis, grafts

Fractures

Physiologic Uptake

FDG subcutaneous infiltration

Physiologic Uptake

Tonsillar Hyperplasia

Talking

Nakamoto. Radiology 2005;234;879-885

Physiologic Uptake

Physiologic Uptake: Brown Fat

Brown Fat

• What is brown fat?

• Methods to reduce FDG uptake

Heat

Reassurance

Sedatives Beta blockers

74 yr old man with seizures and recent cognitive disorder

Adenoma

70 yr old man 2 months post chemoXRT for R piriform sinus cancer stage 3, T3N2M0.

Adenoma

63 y/o man 4 months post chemoXRT for R tonsil cancer T2N1M0

Adenoma

51 yr old man with colon cancer treated with rectosigmoid colectomy and adjuvant chemotherapy.

SUV adrenal 4.0SUV liver 2.2

Adenoma

Adrenal adenoma

Adenoma

82 year old man with wt loss and liver mass

Question 1

Which of the following neoplasms have been associated with focal FDG uptake in the colon?

a. Hyperplastic polyp

b. Adenomatous polyp

c. Adenocarcinoma

d. All of the above

Question 1

Gollub et al. Combined CT Colonography and 18F-FDG PET of Colon Polyps: Potential Technique for Selective Detection of Cancer and Precancerous Lesions. AJR Am J Roentgenol. 2007 Jan;188(1):130-8.

d. All of the above

The correct answer is

Friedland et al. 18-Fluorodeoxyglucose positron emission tomography has limited sensitivity for colonic adenoma and early stage colon cancer. Gastrointest Endosc. 2005 Mar;61(3):395-400.

Nodular Hyperplasia

74 y/o man with metastatic disease to neck from unknown primary, now NED after chemoXRT

Infection

68 year old man with solitary lung nodule. Biopsy: aspergillosis

Granulomatous Disease

62 year old man with hilar and mediastinal adenopathy. Biopsy: sarcoidosis

Miscellaneous Causes

Thyroiditis

Miscellaneous Causes

Rib Fracture

Problems with CT

Attenuation and scatter

Beam hardening

Volume averaging

Beam Hardening

Gollub et al. J Nucl Med 2007;48:1583-1591

Beam Hardening

Volume Averaging

Gollub et al. J Nucl Med 2007;48:1583-1591

Problems with PET/CT

Patient movement

Respiratory misregistration

Attenuation correction

• Head movement

Secure head, or use head holder

Patient Movement

• Respiratory variation

from Ben Yeh MD, UCSF

Partial expiration best:

“Breathe in, exhale, don’t breathe”

Respiratory Misregistration

Respiratory Misregistration

Sureshbabu and Mawlawi. J Nucl Med Technol 2005;33:156-161

Question 2

Respiratory misregistration in PET/CT is minimized when

a. CT is performed in end inspiration

b. CT is performed in mid expiration

c. CT is performed in end expiration

d. CT is performed during quiet breathing

Question 2

The correct answer is

b. CT is performed in mid expiration

Sureshbabu W, Mawlawi O. PET/CT Imaging Artifacts. J Nucl Med Technol 2005;33:156-161

Attenuation Correction

Sureshbabu and Mawlawi. J Nucl Med Technol 2005;33:156-161

Attenuation Correction

Sureshbabu and Mawlawi. J Nucl Med Technol 2005;33:156-161

Summary

• False negative FDG PET can be reduced by careful patient selection for appropriateness and proper preparation

• False positive FDG PET can be reduced by correlation with CT and knowledge of potential pitfalls

Summary

• CT artifacts can be avoided by optimizing technique

• PET/CT artifacts can be reduced by proper patient preparation and instructions