First a safety note. Calibrations involve large, unshielded sources of radioactivity. Please minimize your exposure: Once each calibration is started try to stay out of the room until it is finished. Also, it is an NRC violation to leave so much radioactivity unsupervised. Please put up one of the "Do Not Enter" signs from the Control Room and lock the door whenever you leave.
Calibrations are done with Tc-99m. Since this calibration will affect every scan until the next calibration is performed, it is very important that the flood source be prepared properly. Janet strongly recommends following this procedure: Take the fillable flood source from the safe in the Hot Lab. Make sure that the air bubble is under the two fill screws. Open one fill screw and check the size of the air bubble. If the bubble extends outside of the bubble chamber, add water until the bubble is small enough to completely fit within the chamber. Then use the 60ml syringe in the Hot Lab to withdraw ~50ml of water. Add 22-25 mCi of Tc-99m (no more than that) to flood and replace the fill screw. WARNING: don't over tighten the screw or its O-ring won't seal and the flood will leak. Check for leaks. Then tilt the flood back and forth for 20 seconds, making sure that the air bubbles travel through the center as well as around the edges so the activity gets mixed well. Open the screw and replace 40ml of water, replace screw and mix again. Then replace the rest of the water. Install the LEHR-PAR collimators on the camera and mount the source on the foot support. Please use the level to make sure the source is level both left to right and head to foot. Also make sure that the flood holder is square with the gantry. Finally, check that all air bubbles are within the bubble chamber, not out in the rest of the source.
On the CAP, select Item 1. Flood Quality in the Main Menu and select the Daily Flood protocol. You can reduce the number of counts to 5000K. Once the acquisition is complete, check the image to make sure the source is well mixed and there are no drops of concentrated activity on the outside.
Open the manual that says "Prism 1000 Prism 2000" on the spine to Chapter 3 on QC, and find the Energy/Flood Calibration procedure. It is marked with a yellow Postit note labelled CALIB. The manual has a step-by-step description of what to do. This sheet of instructions is intended to supplement the manual, not replace it.
From the Main Menu select Item 6. System, then Item 3. Calibrate, 3. Energy & Flood, 2. Collimated, and 1. All Heads. Accept the default answers for smoothing, number of counts, and flood table name. Once the calibration is running, lock the door and place one of the "Do Not Enter" signs from the Control Room on the door.
The program runs the energy calibration first then the flood cal. On rare occasions the energy calibration goes awry. Either (1) the creation of the energy table ends prematurely or (2) a value in the energy table goes to an extreme and gets "stuck" there. The symptom of the first problem is that once the flood calibration starts, the persistence image on the CAP looks "hole-y", i.e. has large, obvious nonuniformities. If you see this symptom, abort the calibration. The symptom for the second problem is that the flood calibration finishes but new flood tables are NOT created. You can check for this once the calibration finishes by opening a Unix shell and typing the word "tables". Check that the dates of the lehrp.ft1 and lehrp.ft2 files are today's.
You can confirm that an energy table is bad by displaying it on the CAP. Select item 6. System from the Main Menu, then item 3. Calibrate then 2. Energy then 5. Display. It will ask which head to display. Type 1 or 2. A good energy table looks very low-noise (has lots of counts), and has a periodic pattern of "shadows" corresponding to the positions of the PMTs. The only white pixels should be around the edge. Unfortunately, if there is a problem with the energy table you must restore a good copy off the site tape before re-starting the calibration. The reason is that the program uses the current energy table as the starting point for the new table. If the current table is wildly wrong, the program can't compensate.
If you've determined the current energy table is bad (see Section C above), you must restore a good copy off the site tape before re-starting the calibration. The reason is that the program uses the current energy table as the starting point for the new table. If the current table is wildly wrong, the program can't compensate. Find the site tape with the most recent date (there are 2 tapes/camera) and put it in the tape drive. On the VP computer use the middle mouse button menu and select Save/Restore Site Tape. It will ask "Do you want to continue?" Type y. Then it will give four options. Select option 4, Restore SELECTED Items From Tape. It will ask "Is the tape ready?" Type y. The computer will copy everything from the site tape into a temporary holding area. When it finishes it will give you a list of types of files you can restore. Select Energy Tables. Once it restores the older energy tables, exit the program. Now go back to the CAP and select Item 6. System from the Main Menu, then Item 1. Set Status, then 5. All Corrections. Wait a minute until the screen refreshes. Then restart the Energy & Flood calibration.
To document the magnificent new calibration you've just accomplished, please run a regular daily flood AFTER ROTATING THE FLOOD SOURCE 180 DEGREES IN ITS HOLDER. A good-looking daily flood is confirmation that the calibration went well. If the daily flood has broad nonuniformities, the most probable reason is that the source wasn't mixed well enough before the calibration. Rotating the source 180 degrees between calibration and daily flood ensures you will detect this problem. If the daily flood is nonuniform please re-mix the flood source and repeat Steps B through E.
The previous calibration changed the energy tables. Therefore, the medium energy collimators can't be used until a flood calibration has been run on them. If for any reason you do the first calibration but are unable to do this second cal, please leave a note and make sure Janet knows so it can be run ASAP.
Once you've installed the MEGAP-PAR collimators, re-level the flood source. Then from the Main Menu select Item 6. System, then 3. Calibrate, 1. Flood (not 3. Energy & Flood), 2. Generate, 2. Collimated, and 1. All Heads. Consult the Prism 1000 Prism 2000 manual for step-by-step instructions (section marked with Post-It note). Once the calibration is running, lock the door and place one of the "Do Not Enter" signs from the Control Room on the door. If there is time, please run a regular daily flood afterward, rotating the source 180 degrees beforehand.
If you've run other cals but don't have time to do this one, please leave a note for the QC tech telling them to use Tc-99m for the next day's QC. If you do have time:
(a) Change back to LEHR-PAR collimators.
(b) Mount the Co-57 source in the flood holder and level it (it weighs less than the fillable flood so the head-to-foot level will be off).
(c) On the CAP select Item 4, PHA, in the Main Menu and change the isotope selected to Co-57: move the cursor to the Isotope field so it is highlighted and hit the space bar once. The word "Co57" should appear. Hit Return to select that isotope.
From the Main Menu select Item 6. System, then 3. Calibrate, 1. Flood, 2. Generate, 2. Collimated, and 1. All Heads. Accept the default answers except DO NOT hit Return in response to "Enter 9 character flood table name". If you do, you will overwrite the table created in Step 1**. Instead please type: lehrpco57. Once PHA display appears, hit DO button twice: once to show Head 2's PHA, a second time to start the cal. The words "Acquiring Flood Calibration" should appear. Once the calibration is running, lock the door and place one of the "Do Not Enter" signs from the Control Room on the door.
**Note: If you inadvertently hit Return for this question, immediately abort the calibration by typing Control+Break. Type menu at the '$' prompt and restart the Co-57 calibration. Flood calibration
