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Tips when Reading Non-Enhanced CT images in PET/CT Studies

* Adrenal nodules on non-enhanced CT images with attenuation < 10 HU are most likely fat-containing adenomas even if focally FDG-avid.

"The presence of intracytoplasmic lipid within adenomas has been found to accurately separate adenomas from malignant lesions. On unenhanced CT, a threshold of 10 Hounsfield units (HU) or less suggests the presence of intracytoplasmic lipid, and therefore an adenoma, with a sensitivity of 71% and specificity of 98% (10). Despite the high specificity of this parameter—enabling diagnosis of lipid-rich adenomas with a high degree of certainty—approximately 30% of adenomas are lipid poor, with higher attenuation values overlapping those of other adrenal masses, including malignancies." (Metser U et al. JNM 2006.)

Common Pitfalls in FDG PET Interpretation

There can be abnormal FDG activity at sites of interest for reasons unrelated to disease.

Due to post-radiation changes, it is prudent to wait at least 6 weeks to assess a lesion treated by radiotherapy. In some cases, post-radiation changes can take up to 6 months to resolve.

Source
Lee P et al. Current concepts in F18 FDG PET/CT-based radiation therapy planning for lung cancer. Front Oncol. 2012; 2: 71.
Schuster DM. Limitations & Pitfalls of PET PET-CT in the Head and Neck. PowerPoint presentation, date not listed.

Helpful Reviews

FDG PET/CT for Oncology Imaging

Kapoor V et al. An Introduction to PET-CT Imaging. RadioGraphics 2004; 24:523–543.


Segall G. Problems and Pitfalls in the Interpretation of PET/CT. Hosted by SNMMI. Accessed 6 Nov 2014.


NaF PET/CT for Skeletal Imaging


Bastawrous S et al. Newer PET Application with an Old Tracer: Role of 18F-NaF Skeletal PET/CT in Oncologic Practice. RadioGraphics 2014; 34: 1295–1316.



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