Power of PET/CT
The power of PET/CT lies in its fused hybrid nature: the ability to combine a functional exam, relatively specific and sensitive for malignancy, with an anatomic exam, permitting precise localization of a functional abnormality.
Quick Whole Body Assessment of the Extent of Disease:
This single, whole-body exam readily permits both an anatomic assessment of the entire body and a relatively sensitive and specific whole-body functional assessment of any potential sites of metabolically active malignancy.
Often just a brief glance at the whole body MIP images readily illustrates its tremendous diagnostic potential in an oncologic work-up.
The “You’re Kidding Me!” Effect:
This not infrequent phenomenon of unintentional vocalization by the radiologist occurs after he or she ignores an unassuming solitary 5.0-mm lymph node while reading the CT portion of the exam – a node no CT radiologist would ever mention in a CT report – only to find that it lights up like sun on the PET portion of the exam (frequently, the utterance is a bit more “colorful”…).
Would you have questioned this metastatic left internal mammary lymph node if this had only been a CT scan?
PET/CT will regularly reveal active malignancy in extremely small lymph nodes, millimetric lesions in solid organs, or multiple skeletal lesions that would simply not be detected with conventional CT imaging alone. [Fig. 1] [Fig. 2] [Fig. 3]
Post-Therapeutic Scar vs. Active Malignancy:
PET/CT is unsurpassed in its nearly unique ability to determine whether residual soft tissue density after therapy represents persistent active malignancy or simply benign scar tissue/fibrosis (addressed in detail, here).
Post-treatment scan of this lymphoma patient (images above) demonstrates resolution of the patient’s prevascular lymph node and a decrease in size of the large right mediastinal node. We know there has been improvement, but does this remaining soft tissue represent residual active disease or scar tissue? Does the patient need more chemotherapy or is this patient is now cancer free?
To answer this critical question, we must turn to the PET portion of the exam:
The remaining soft tissue is now non-avid (uptake less than adjacent mediastinal blood pool in this case), consistent with post-therapeutic scarring. There is no evidence of active disease at this time.
