Performance evaluation of prototype thyroid uptake probe made by Bhabha Atomic Research Centre

The thyroid uptake probe is an integral part of a nuclear medicine department that investigates thyroid disorders. It is used to estimate the radioiodine uptake in the neck following the administration of a small amount of radioactive iodine-131. The probe comprises of - a flat field collimator, NaI (Tl) crystal, photomultiplier tube, preamplifier, amplifier and a counter/scalar unit. Performance of the thyroid uptake probe is evaluated by carrying out – counting statistics and χ2-test, detector shielding test, sensitivity test, stability test, linearity of response, energy resolution etc. These tests were applied to the prototype thyroid probe made at Bhabha Atomic Research Centre, to check its suitability for routine use. Aims: To evaluate the Bhabha Atomic Research Centre thyroid probe by carrying out the various performance tests prior to its use for routine uptake studies. The Electronics Division, Bhabha Atomic Research Centre, developed a thyroid uptake probe with interface electronics and required software to use it with a standard PC. This stand-alone machine was evaluated for its performance at RMC. Its counting statistics and χ2-test of observed and expected counts was carried out with a suitably placed 25mCi ¹³¹I capsule,. Detector shielding test was performed by placing a ¹³¹I source in various positions viz., front, sides, back, close left, close right etc. Sensitivity of the probe was calculated using known ¹³¹I and ¹³⁷Cs sources. Linearity of radioactivity response was compared using ~0.5mCi/100μl of ^99mTc and taking counts at different time intervals. Energy resolution was by plotting energy spectrums using ⁵⁷Co, ¹³⁷Cs, ¹³¹I and ^99mTc sources. Linearity of energy response was also performed. I response curve was drawn using ⁵⁷Co by keeping the source at different locations in front of the uptake probe. An old thyroid probe (still in use at RMC) manufactured by Nuclear Chicago, USA, about 30 years ago and, which is an industry standard was also evaluated for comparison. Results: The thyroid uptake probe made in Bhabha Atomic Research Centre was found to have acceptable performance parameters. Moreover, the fabricated probe showed better sensitivity and percent energy resolution than the old uptake probe. Conclusions: The Bhabha Atomic Research Centre made thyroid uptake probe had acceptable performance parameters and is suitable for patient use. The computer interface and software enabled user-friendliness and patient through-put. (author)