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Comprehending the PET

Almost every lung cancer survivor has a positron emission tomography (PET) scan these days. Now, a PET is often given with a computerized axial tomography (CT) scan.  The diagnostician is a radiologist; a discipline that does not write in lingua franca. What do the report words mean? Here is a summary of my August PET-CT to interpret radiology speak.

INDICATION: (Why am I getting this scan) “The patient…with non-small cell lung cancer of the right main bronchus diagnosed in 2003 status post pneumonectomy….He has undergone previous surgery for bronchopleural fistula repair…Chemotherapy last administered May 2006…Cyberknife therapy for recurrent disease in March 2007…He more recently has cough and chest discomfort.” That’s me, no doubt, but this summary is important.  Radiologists see many scans and sometimes results are misreported.

TECHNIQUE: (Test scope and method)  Note details about the accuracy of the CT.  “These images do not constitute a diagnostic-quality CT….” The CT results help to precisely map or locate the PET results but cannot generate a diagnostic grade image.

COMPARISON: (Other scans reviewed while looking at this one). “Report only (no image reviewed) from PET-CT 3/8/2013.  CT of chest and abdomen 8/22/17 (looked at image).”  A CT scan is normally performed first.  PETs follow and accuracy is enhanced if the radiologist has access to prior images. To improve access, have all your scans done at the same medical facility.

FINDINGS: (The result) “…showed no convincing PET evidence of FDG-avid (fluorodeoxyglucose — radioactive tagged glucose seeking) recurrent or metastatic disease.” This is what we want to see in the first sentence.  Then, the radiologist peels back the onion with detail.  

“There is mild heterogeneous hypermetabolism (diverse increased rate of metabolic activity)…with a few small superimposed foci (above the hypermetabolic area that is of particular interest)…more intense activity showing a maximum SUV of 3.5 (SUV — standardized uptake value)….When compared to [past reports] uptake…showed SUVs ranging from 2.6 to 2.9. This is strongly favored to be inflammatory.” Relief —this is my chronic pain site caused by 3 thoracic surgeries in the same location!  

“A somewhat retractile appearing mass (drawn back into lung tissue)…in the left upper lobe is stable in size…This shows minimal uptake…and is most compatible with the site of treated tumor.” My CyeberKnife-fried tumor scar.  I do love precision radiation!

What are concern ranges for SUV uptake? First, consider what is measured — cellular metabolic rate; more simply is demand for glucose, the fuel of metabolism.  Cells with high metabolism ingest more tagged glucose. The PET shows differences in consumption (uptake).  SUVs below 2.0 are normal.  SUVs above 2.0 are suspect but between 2.0 and 4.0, uptake could be from injury or inflammation.  Readings above 4.0 tend to be cancer but there can be other explanations. Higher than 4.0 is likely cancer, especially when paired with a CT find. Cancer demands glucose to fuel mitosis or growth by cellular division.  

Get and keep copies of all your diagnostic imaging.  Keep track of the findings.  I use a spreadsheet to record date, location and indications.  Dr. Google is a great source for medical definitions. The best possible outcome for any scan is NED (no evidence of disease).  May NED be with you.

Stay the course. 

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