camera issues

 

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There are several camera issues to take into account when imaging with Kr81m.

Secondary Shield

The generator will increase the background level on the camera and this must be kept to an acceptable value.  It is important to carry out your own check of the background countrate.

Typically, a secondary shield will need to be used and a typical specification is given.

 

Collimator Issues

Can a Tc99m collimator can be used with Kr81m? Some can be used but there is no easy answer. The simplest solution is to carry out a phantom study. It is possible to obtain a guide by calculating the septal penetration from the collimator parameters.

Collimator sensitivity is another issue. A high resolution Tc99m collimator may be too insensitive. Try a medium energy collimator for both Tc99m and Kr81m lung images.

It may be necessary to specify a collimator. This could be designed for 191kev or  If it is as part of a new camera purchase then it might replace the manufacturer's general purpose Tc99m collimator.

 

Daily QA

A daily QA programme should be part of any gamma camera routine. There are a few additional QA issues which should be carried out before the Kr81m generator is used clinically.

 

Dual Energy Acquisition

It is possible to acquire the Tc99m perfusion image and the Kr81m ventilation image simultaneously using a dual energy window acquisition protocol. However there will be downscatter from the Kr81m into the Tc99m window. It is important that this does not form a significant proportion of the Tc99m images. This issue will become more significant with a more active Kr81m generator. Few cameras have separate stop conditions for each energy window and you should know how your camera operates in dual energy mode.  Therefore it is important that you assess the amount of downscatter if you want to use dual energy acquisition.

 

 

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Last modified: November 29, 2002