CT and SPECT image registration and fusion by using the external fiducial markers allow precise anatomical location of sentinel lymph nodes in breast cancer

Objectives Lymph node status is a major factor in determining the stage in patients with breast cancer. It is therefore of clinical importance to accurately identify all sentinel nodes (SNs) before surgery. Therefore, the fusion of Chest CT and SPECT images can provide more precise anatomical information than planar images. The purpose of this study was to confirm the feasibility of CT and SPECT image registration by using external fiducials for visualization of SNs in breast cancer without expensive hybrid SPECT/CT.

Methods Pre-operative lymphoscintigraphy using Tc-99m phytate colloid was performed in 70 consecutive patients with breast cancer (mean age 55.3±11.8). Continually, SPECT and low dose chest CT was performed by using an Am-241 contained button as the external fiducial marker which is attached to the skin surface of the patients’ chest wall. The acquired SPECT and CT images were rescaled, interpolated, reformatted and followed by point-to-point registration on a workstation.

Results SPECT can detect sites of SNs including level I (n=86), level II (n=10) and internal mammary (n=7). On the fused images, the precise overlap of hot spots on the correspond lymph nodes of CT images could be realized in all but two cases. In the cases that have axillar lesions, rendering fused images into 3D volumes with accentuated pectoralis minor muscle can add helpful for the difference diagnosis of SNs location between level I and II. After surgery, 14 metastatic nodes are confirmed by histological examination and all nodes could be depicted as “hot nodes” by fused images.

Conclusions External fiducials based co-registration between lymphoscintigraphy SPECT and CT can depict the precise location of the SNs drainage and give useful information for pre-operative planning without hybrid SPECT/CT.