Figure 1.
Figure 2.
Imaging P.E.T./CT Scan in Nuclear Medicine P.E.T./CT Hodgkins Lymphoma Staging & Re-staging
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Patient History
The patient is a 42 year-old female. She had a benign left biopsy in1982, she now complains of a palpable mass in the left axilla. After a standard mammogram( 11/22/02) of both breasts it was stated that she had multiple large masses in the left axilla that needed further investigation. The patient then had a CT with contrast of the thorax (01/24/03), which demonstrated lymphadenopathy in the left axilla. A whole body P.E.T./CT was performed (01/16/03) for staging of the lymphoma. This scan showed multiple enlarged nodes in the left axilla with a maximum SUV of 11.1, which is consistent with malignancy, there were no other areas of increased tracer activity. Following chemotherapy another whole body P.E.T./CT was performed for re-staging of the lymphoma. The results of this scan stated that the lymphoma that was detected on the previous P.E.T./CT was undetectable, there were no focal areas of increased FDG uptake
Patient Preparation:
The patient was instructed to fast 6 hours prior to the scan, except water. Is fasting required for all PET scans? Why, or why not? Upon arrival the procedure was explained to the patient. An IV was inserted to administer the FDG and then immediately removed.
Radiopharmacy:
The patient’s first dose for the staging was 12.3 mCi and the second for the re-staging was 12.0 mCi. What is the standard dose range for F-18 FDG? After the injection of FDG the patient was instructed to sit quietly for 45 minutes to 1-hour. Why is this necessary?
Imaging and Positoning:
The patient was instructed to void urine and remove all metal objects from her person to avoid creating artifacts on the images. She was positioned on the table supine/head first and covered with a blanket. Her arms were extended over the head so that they were not overlying the area of interest (the axilla). The patient was instructed to remain still and breathe normally
Instrumentation and Processing:
The instrument used for this scan was a General Electric discovery LS and light speed CT. The 8 slice, spiral CT was acquired in continuous mode at 120 mA and 140 keV with a rotation of 0.8 s and pitch of 1:1. The PET portion of the scanner has a BGO crystal, which has excellent spatial resolution and about the same decay time as the LSO crystal. 2D collimation was used for this scan, this means that the septa are in. What’s the advantage of 2D collimation? The advantage of placing the septa between the detectors is to promote higher spatial resolution. The CT portion of the scan was performed first seconds, and then the PET scan was acquired for approximately 20-30 minuets. Does it matter whether the CT or PET scan is performed first, or is it alright to do either one first? The importance of performing the CT scan prior to the PET acquisition is not only to provide anatomical information, but also to create a transmission map to be used in attenuation correction for the PET images. This map allows for the fusion of the CT and PET images to be precisely aligned within the same perimeters.
Findings:
In this case the diagnostic value of P.E.T./CT is very well demonstrated. The first scan was for staging of the lymphoma and the second scan was for re-staging to evaluate the impact of the treatment. After the mass was located on the mammogram and followed up by chest CT with contrast, the P.E.T./CT proved to be a valuable tool in deciding a course of treatment. With the first scan the physicians learned that this was a case of malignancy, they were then able to decide how to treat the patient. The decision was to proceed with a course of chemotherapy. The second scan was performed after the treatment, which showed no areas of focal uptake.
The pre and post treatment P.E.T./CT images were valuable in the success of this patient’s treatment. The pre-treatment images allowed the physicians to determine how far progressed the disease was and if it was treatable. Once it was determined that this was the only area of cancerous tissue, it was decided that chemotherapy would be the best course of action to cure the patient.
The post treatment images were valuable in showing that the chemotherapy was successful in curing (what is the definition of cure?) the Hodgkin’s lymphoma.