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Lung Mass Evaluation with F18FDG
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Amanda Brautigan, CNMT, RT(N)
Senior Student NMT, Medical College of Georgia


Rufus Poole, CNMT, Chief Technologist
Emory Univeristy Hospital, Department of Nuclear Medicine


Mary Anne Owen, MHE, RT(N)
Program Director, Nuclear Medicine Technology
Medical College of Georgia



Discussion (click to view)

The standard uptake value (SUV) is a way of quantifying FDG uptake on a PET scan. The SUV is calculated with a mathematical equation that divides the mean activity within a region of interest (in mCi/mL) by the injected dose (in mCi/kg).


Any value calculated at greater than 2.5 is considered to be very sensitive and specific for malignancy. Therefore SUVs of 4 all the way up to 10 are very unfortunate for this patient’s diagnosis.


This quantification method gives confidence to the radiologist when reading by assigning a number to compare to normal, much the same as with a CCK HIDA of left ventricular ejection fraction.


Even with the use of SUVs there can still be false positives when it comes to lung cancer. Some pathologies that may cause false positives include: infectious and inflammatory lesions and aggressive neurofibromas. One very important false negative is bronchioalveolar carcinoma. This carcinoma is on the low end of metabolic activity.



Patient History


59 year old white female, smoker for 30 years two packs a day…quit 6 years ago. She has been coughing up blood with a persistent cough and difficulty breathing. A mass appeared in her lung on CT, but she has had two negative bronchial washes.



Findings


With no CT available from the hospital for comparison, the exact location of the increased areas of increased uptake are unknown at the time of dictation.

Instructor's Comments:
Q: What steps could be taken to prevent this shortfall in the future?

 

There are several areas of intense focal F18 FDG uptake in the left superior mediastinum and left posterior hilum. Standard uptake values (SUV) were calculated and reported at 4 for some areas and others were as high as 10. These uptake values are most definitely associated with malignancy.

Instructor's Comments:

Q: What are the significant ranges or values for SUV?



Radiopharmacy


10.6 mCi of F18 FDG were injected intravenously and the patient then rested quietly in a room alone for 45 minutes.

Instructor's Comments:
Q: Why Rest?



Procedure


At 45 minutes the patient was asked to empty her bladder to minimize her dose and shine from the increased activity on her PET scan…and with hopes of getting a clear image of her pelvic area.



Positioning


The patient was laid down on the table and positioned with her arms above her head for a whole body scan.


Instructor's Comments:

Q: Did the patient lay down in a supine or prone position?

Q: How is the posiitoning different from SPECT imaging, if at all?



Instrumentation


In the computer, whe was set up for 4 beds meaning the scanner would move to 4 different positions to acquire counts from her nose to below her pelvis. This is a length sufficient to provide diagnostic information.


The acquisition was performed with the septa out to increase the resolution and acquire as many true counts as possible. There are upper and lower level discriminators built into the software at 250 and 650 keV to account for the 511 keV of the positron annihilation reaction and enough scatter to provide a desirable target to background ratio.


Instructor's Comments:
Q: What does it mean when there are upper and lower level discriminators?

Processing


Instructor's Comments:
Q: How are these studies processed?


May 2002