To assess the most appropriate device in PET/CT for the evaluation of patients with breast cancer in prone position.
PET/CT Philips Gemini TF Big Bore has been used for acquisitions scan. A second acquisition of the thorax for the study of the breast in prone position 2 p.i. was added to the classical 18F –FDG PET/CT protocol in supine position at one hour.
The CT parameters used for the second acquisition were:
120 kV, 80 mAs pitch 0.813 , 16×1.5mm collimation , FOV 600.
The PET parameters in PET were: 2 min for bed position, FOV 576 mm , 2.5 MBq / kg of 18F- FDG.
The images in prone position were acquired using three different immobilization devices of the breast. At the beginning for the first 3 patients we used a pressure mattress in which we created cavities to accommodate the breasts. Subsequently, for the next 2 patients a Magnetic Resonance Mammography (MRM) coil was utilized. Finally, we opted for an MRM coil without its metallic circuits in 100 consecutive patients.
It was evident that images in prone position enhanced the evaluation of the breast lesions respect to studies in supine position. The first two devices had some important limitations.
The pressure mattress was affected by the weight of the patients and tended to squash the breast and consequently the images showed a less elongation of the breast with respect to the images obtained with the MR coils.
The integral MR coil allowed a complete separation of the breast structures independently of the weight and size (limit of pressure mattress), but the quality of the images were affected by the presence of artifacts due to the electronic circuits.
Therefore the evaluation of PET images was carried out without attenuation correction (NAC) .
The emptied MR coil solved these problems both with a comprehensive volumetric representation of the breast and the elimination of beam hardening artifacts . In all one hundred patients we had high quality images without any artifacts.
The use of emptied MR breast coil is the best compromise for high quality PET/CT images in prone position. The use of the same type of coil in PET/CT and MRM could make image fusion easier and more accurate and it might compensate for the absence of a hybrid PET/MR.