George Segall, M.D.

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Problems and Pitfalls in the Interpretation of
PET/CT
George Segall, M.D.
Stanford University
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False Negative FDG PET
Low-grade glioma Low-grade lymphoma Bronchoalveola
r lung cancer Hepatoma Renal cell
carcinoma Prostate cancer
Histology
Size
lt 10 mm
Post prandial scans
Hyperglycemia
gt 150 mg/dL
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Post Prandial Scan
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.
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Post Prandial Scan
Fasting
Euglycemia 6 hours Diabetes 12 hours
fasting 05/08
fed 04/25
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Fasting Scan in a Diabetic
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.
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Hyperglycemia
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)
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Insulin Effect on FDG uptake
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)
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False Positive FDG PET
Physiologic
Benign Neoplasm
Adenoma
Inflammatory
Granuloma, sarcoid, rheumatoid
Miscellaneous
Prosthesis, grafts
Fractures
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Physiologic Uptake
FDG subcutaneous infiltration
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Physiologic Uptake
Tonsillar Hyperplasia
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Physiologic Uptake
Talking
Nakamoto. Radiology 2005234879-885
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Physiologic Uptake Brown Fat
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Brown Fat
What is brown fat?
Methods to reduce FDG uptake

• Reassurance

• Heat

• Sedatives

• Beta blockers

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Adenoma
74 yr old man with seizures and recent cognitive
disorder
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Adenoma
70 yr old man 2 months post chemoXRT for R
piriform sinus cancer stage 3, T3N2M0.
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Adenoma
63 y/o man 4 months post chemoXRT for R tonsil
cancer T2N1M0
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Adenoma
Adrenal adenoma
SUV adrenal 4.0 SUV liver 2.2
51 yr old man with colon cancer treated with
rectosigmoid colectomy and adjuvant chemotherapy.
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Adenoma
82 year old man with wt loss and liver mass
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Question 1
Which of the following neoplasms have been
associated with focal FDG uptake in the colon?

1. Hyperplastic polyp

b. Adenomatous polyp
c. Adenocarcinoma
d. All of the above
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Question 1
The correct answer is
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
Jan188(1)130-8.
Friedland et al. 18-Fluorodeoxyglucose positron
emission tomography has limited sensitivity for
colonic adenoma and early stage colon cancer.
Gastrointest Endosc. 2005 Mar61(3)395-400.
d. All of the above
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Nodular Hyperplasia
74 y/o man with metastatic disease to neck from
unknown primary, now NED after chemoXRT
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Infection


68 year old man with solitary lung nodule.
Biopsy aspergillosis
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Granulomatous Disease
62 year old man with hilar and mediastinal
adenopathy. Biopsy sarcoidosis
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Miscellaneous Causes
Thyroiditis
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Miscellaneous Causes
Rib Fracture
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Problems with CT
Attenuation and scatter
Beam hardening
Volume averaging
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Beam Hardening
Gollub et al. J Nucl Med 2007481583-1591
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Beam Hardening
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Volume Averaging
Gollub et al. J Nucl Med 2007481583-1591
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Problems with PET/CT
Patient movement
Respiratory misregistration
Attenuation correction
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Patient Movement
Head movement
Secure head, or use head holder
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Respiratory Misregistration
Respiratory variation
Partial expiration best
Breathe in, exhale, dont breathe
from Ben Yeh MD, UCSF
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Respiratory Misregistration
Sureshbabu and Mawlawi. J Nucl Med Technol
200533156-161
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Question 2
Respiratory misregistration in PET/CT is
minimized when

1. 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
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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 200533156-161
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Attenuation Correction
Sureshbabu and Mawlawi. J Nucl Med Technol
200533156-161
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Attenuation Correction
Sureshbabu and Mawlawi. J Nucl Med Technol
200533156-161
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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
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Summary
CT artifacts can be avoided by optimizing
technique
PET/CT artifacts can be reduced by proper
patient preparation and instructions
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