Introduction
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Uniformity test is important and performed every morning in the nuclear medicine department on gamma camera.
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This test can be performed either by intrinsic or extrinsic method.
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There are multiple methods of performing uniformity test.
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Extrinsic Uniformity is performed without removing the collimator, which ensures the system performance including collimator performance.
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Most of the centres perform daily uniformity test by this method.
Phatoms available:
- Two options are currently available to perform daily extrinsic uniformity-
- 99m Tc fillable flood field phantom
- 57 Co Sheet phantom
141 Ce Phatom
- Indigeneously developed 141 Ce fillable phantom is an alternative.
- It also negates the dependency on imported solid 57 Cobalt sheet source phantom.
- Charging of 141 Ce phantom requires once in 50 days and exposure to the professional during the charging of phantom is around 9 microSv.
- It saves professional effort and radiation exposure to the professional.
- Beta emissions by 141 Ce is soft beta and hets attenuated by perspex of the phantom.
99m Tc flood field phantom
- 99m Tc is the workhouse isotope to perform various diagnostic procedures on gamma camera.
- 99m Tc flood field phantom is the most suitable phantom to perform quality control on a gamma camera.
- Other than the process being cumbersome and tediuos, this phantom also poses extra radiation burden to the radiation professional involved.
57 Co Phantom
- It is widely used because of its closest photopeak energy (122kev) with that of 99m Tc (140kev), its long half life of 271 days and its availability in the form of readt to use sheet phantoms.
Advantages of 141 Ce Phantom
- Photopeak of 141 Ce (145kev) is closest to that of 99m Tc and hence may be a suitable replacment of 57 Co phatom.
- The integral uniformity of 141 Ce filled phantom is comparabel with that of 57 Co flood field phantom.
- The average radiation exposure rate at surface and one meter from 141 Ce flood field phantom is also found to be comparable to that of 57 Co flood field phantom.
- Cost wise it is comparable to Co 57 phantom.
Diadvantage of 141 Ce Phantom
- Despite all positive points and encouraging results, production and periodic supply of 141 Ce isotope needs to be assured by the suppliers for the use of nuclear medicine department.
- Production of 141 Ce isotope is a cumbersome process and demanding and requires lots of efforts and technical expertise.
- Extra radiation safety precautions need to be taken to avoid any major spillage of 141 Ce isotope during phantom preparation.
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References
A novel Cerium-141 based flood field uniformity phantom: Assessment of its suitability to perform daily uniformity test in a clinical nuclear medicine department - Journal of Nuclear Medicine Technology Apr 2017, jnmt.116.189340