Axillary lymph node status in breast cancer: Pinhole collimator single-photon emission computed tomography

This chapter demonstrates the clinical value of pinhole-single photon emission computerized tomography (SPECT) in breast cancer patients for axillary lymph node status evaluation, with 99mTc-tetrofosmin as radiotracer. In each patient, after obtaining written informed consent, 740 MBq of 99mTc-tetrofosmin is injected in the controlateral arm of the suspect mammary lesion, and when bilateral disease is suspected, the radiotracer is injected in a pedal vein. Axillary pinhole-SPECT images are acquired immediately after conventional planar and 360° SPECT scintimammography with parallel-hole collimators, the former acquisition beginning 10 min after tracer injection. Pinhole-SPECT images are acquired over 180° (in clockwise rotation with the step and shoot method) with the patient in a supine anterior position, the arm corresponding to the involved axilla raised over the head. A radioactive 99mTechnetium marker is used to ensure that the axillary region is always at the center of the collimator's field of view. Particular care is given to positioning of the patient to obtain the minimum distance between the center of rotation and the collimator, in all cases within 15 cm. The final position thus obtained determines the starting angle for each individual patient. The images are acquired using a matrix size of 128 × 128 and a zoom factor of 2 as fixed by the software acquisition protocol, an angular step of 3°, and an acquisition time per frame/angular step of 30 sec. Pinhole-SPECT projections are preprocessed by a cone beam algorithm and then processed by the backprojection filter (BPF) method using a Metz filter to obtain 2-pixelwide transaxial slices.