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Reconstructed 3D ultrasound of prostate gland finds application in several medical areas such as image guided biopsy,
therapy planning and dose delivery. In our application, we use an end-fire probe rotated about its axis to acquire a
sequence of rotational slices to reconstruct 3D TRUS (Transrectal Ultrasound) image. The image acquisition system
consists of an ultrasound transducer situated on a cradle directly attached to a rotational sensor. However, due to system
tolerances, axis of probe does not align exactly with the designed axis of rotation resulting in artifacts in the 3D
reconstructed ultrasound volume.
We present a rigid registration based automatic probe calibration approach. The method uses a sequence of phantom
images, each pair acquired at angular separation of 180 degrees and registers corresponding image pairs to compute the
deviation from designed axis. A modified shadow removal algorithm is applied for preprocessing. An attribute vector is
constructed from image intensity and a speckle-insensitive information-theoretic feature. We compare registration
between the presented method and expert-corrected images in 16 prostate phantom scans. Images were acquired at
multiple resolutions, and different misalignment settings from two ultrasound machines. Screenshots from 3D
reconstruction are shown before and after misalignment correction. Registration parameters from automatic and manual
correction were found to be in good agreement. Average absolute differences of translation and rotation between
automatic and manual methods were 0.27 mm and 0.65 degree, respectively. The registration parameters also showed
lower variability for automatic registration (pooled standard deviation σtranslation = 0.50 mm, σrotation = 0.52 degree)
compared to the manual approach (pooled standard deviation σtranslation = 0.62 mm, σrotation = 0.78 degree).
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