Another Myocardial Display Macro

 

There are some really neat features in Pixie Show which aren't so well known (though they are all in the help file for the command). Here we will look at a useful feature which is not even exploited in any of the Odyssey's own factory macros (as far as I know).

 

Exacting slice alignment

Do you routinely have to display stress and rest cardiac images and film or lightbox them? If so you probably like to get them all lined up meticulously and orientated accurately. With standard factory macros (e.g. tomo display) you can only alter the alignment by a whole slice so if you get it wrong its back to reformatting. But there is a slice summing syntax so if you feed in files with slices say 1/5th as thick as you wish to display, you can then adjust the alignment by a fifth of a slice at a time. This is demonstrated in the macro. You can also adjust slice thickness. (To view it, click the link, to download&try, right click the link and select "Save target as", then remove the .wri extension before putting it in your /prism/site directory. Don't open it with wordpad save it and expect it to work, windows editors add invisible line feeds that trip up Pixie)

Getting orientation right

How about the orientation? Well we use Beacon all the time and the factory macros give you tiny images to prescribe slices from, also you process the stress and rest separately so you have to remember exact angles for some minutes. I feel its better to reformat both image sets together so we now do this by using 2 workbenches. We also reduce the pixel size to 3mm (options) which makes the images bigger and is one way to obtain the thin slices we need for the display macro above. We end up prescribing slice on a screen that looks like this. I like the reformat program, it is so flexible, but sadly there is one bug. When you reduce the pixel size, the program will not let you prescribe slices near the edge of the data set. To get round this we run image algebra and do a fixed x and y translate (-12 and 18 resp) on the data to get the heart approx to centre before reformatting. The x and y offset values were found empirically by inspecting 12 sets of patient data. Obviously we combined this in a very simple workbench macro for convenience (macro).

 

Final result

Looks like this (warning for narrow band users its 423kB).

Note the slice thickness and cell size annotation. This is obtained by combining some header information in the files with the magnification and slice thickness currently being used by show.