X-Ray Tube Heat Soak and Seasoning (LS 16, Ultra, Plus)

1 Heat Soak and Seasoning Overview

The Heat Soak and Seasoning program drives the scanner to perform a set of scans, which when taken in the proper sequence and with the correct time intervals between scans can extend the life of CT tubes. This program is run by service personnel whenever deemed necessary through observing the number of tube spits during actual scan operations. The entire protocol consists of three phases that will be executed in sequence.

This program seasons a new tube by first performing a tube heat soak. This process is done to remove any undissolved gases in order to minimize the occurrence of mA overloads.

After the heat soak, a high voltage stability test (Seasoning) is performed to verify that the tube is stable. Real time feedback of high voltage stability is provided to the user in order to determine if the current technique scans must be repeated. Because some of the scans used in this procedure are not used in normal patient scanning, special calibration scans are needed to determine the parameters needed to make these scans.

The Heat Soak and Seasoning procedure can be thought of as a series of alternating calibrations and scans. The particular sequence and parameters differ with the tube’s type. In some cases, tube cooling delays need to be determined so that scans can be completed without need for extra cooling delays.

2 Tube Warm-up

The Tube warm-up phase of the Tube Heat Soak and Seasoning procedure raises the temperature of the tube slowly in order to prepare it for the high power scans that will follow. This phase is extremely important to minimize target damage when it is suddenly subjected to high energy input.

3 Heat Soak

New tubes may have undissolved gases that could render the tube unusable due to excessive arcing. The purpose of the heat soak phase is to redissolve gases in the tube at high temperatures in order to minimize the occurrence of current overloads. (i.e. tube spits).

The Heat Soak procedure consists of three sub-phases, which are: Heat input, Anode Soak and casing Soak. The Heat input and Anode Soak scans are performed in a dynamic series so that additional tube cooling is not necessary during the two sub-phases.

Heat Input

This phase heats the target up to maximum heat storage. This heats the target and other parts of the tube to maximum temperature for proper de-gassing. At the same time, the tube “getter”, a chemical that absorbs gases, is heated up to its activation temperature to absorb the gases in the tube.
Anode Soak

This phase maintains the target at maximum heat storage and maximum temperature to continue the de-gassing and absorption of gases by the getter.
Casing Soak

In this phase, the tube unit is heated up to the casing heat storage limit. This heats the oil to a point where gases can be reabsorbed by the oil.

4 High Voltage Seasoning

High Voltage seasoning eradicates any small micron sized particles that may be in the tube insert. Left in the tube, these particles can become charged and thus, cause arcing. In addition, this segment can be used as troubleshooting tool by the service person to verify that tube operation is stable prior to customer use.

Interruptions during the automated scans are allowed only during the Seasoning phase. If interrupted, scanning can be resumed from the previous scanning station till completion. The state entered on an interruption is called the manual mode.

5 Procedure & Protocols

5.1 Tube Heat Soak and Seasoning Procedure

Select REPLACEMENT.
Select DDC.
Select LOAD PROTOCOL.
Refer to Table 1, and load each protocol individually.

5.2 Tube Heat Soak and Seasoning Protocols

The Tube Heat Soak and Seasoning protocol for the MX_200CT tube (Performix) is given below. Refer to Performix tube replacement procedures. All scans are done with the tube’s large focal spot. The scan time and interscan delays specified in the protocols listed must be rigidly enforced.

The execution of the scans listed must follow certain rules. The tube warm up stage is optional depending on the temperature of the tube. The next five scan groups (Heat Input to Casing Soak 2) must be executed without interruptions (if possible). If the protocol is stopped during this period, it is recommended that this entire group of protocols be executed again. During Seasoning, execution may be stopped at the operator’s discretion and can be either resumed or started once again from the previous scan group.

Table 1. MX_200CT Heat Soak and Seasoning Protocol (Software Version: LIB_H16.80)
MX_200CT Protocol	Scan Group	kV	mA	# of Scans	ISD (sec.)	Scan Time (sec.)	Set Delay (sec.)	Static / Rotate (4.0sec)
warmup1	1	120	200	3	2	5		R
warmup2	1	100	220	7	1	4		R
hss_heat_1	1	80	100	15	2	2		R
	2	80	300	24	2	3	2	R
hss_heat_2	1	100	320	17	5	3		R
hss_heat_3	1	80	100	15	2	2		R
	2	80	300	24	2	3	2	R
	3	100	320	17	5	3	2	R
hss_soak	1	100	320	10	3	1		R
	2	100	270	90	16	2	60	R
hss_season1	1	100	50	10	5	1		R
hss_season2	1	100	50	5	5	1		R
hss_season3	1	100	50	5	5	1		R
hss_season4	1	120	50	5	5	1		R
hss_season5	1	130	50	5	5	1		R
hss_season6	1	135	50	5	5	1		R
hss_season7	1	140	50	10	5	1		R
hss_season8	1	145	50	10	5	1		R
hss_season9	1	150	50	15	5	1		R

6 Hot ISO

Hot ISO is a software procedure that does not require any physical adjustment. It is a set of calculations used to improve image quality due to focal spot movement as the tube is heated.

Hot ISO requires that the tube be heated to near maximum capacity so that the total drift of the focal spot can be measured. Heat Soak and Seasoning (HSS) heats up the new tube to near maximum storage for tube Seasoning. ISO scans are added between the heating scans and the season scans of the HSS feature with minimal impact on both tube change time and HSS.

The ISO values that result from Hot ISO requires four new fields in ScanHardware.cfg (two to store the drift values of each of the spots (small & large) and two to store the ISO values of the cold spots (small & large). These values will also have to be stored in the INFO file for Save/Restore of system state.