Pitfalls in the lateral imaging of the thyroid with pinhole collimators

Imaging of the thyroid gland with pinhole collimators in the lateral projection is associated with the problem of count rate contribution from the contralateral lobe. In a series of experiments conducted using a thyroid-simulating phantom, the contribution of this nature was calculated. Radioisotopes of different energies such as 99mTc and 131I were used to see the effect of energy on this contribution. It was observed that the count rate contribution from the contralateral lobe to the lobe proximal to the collimator can be as high as 70% at a distance of 6 cm from the collimator. At distances more than 6 cm these contributions from the contralateral lobe are much more than this.