Please consult this lists with frequently asked questions before contacting Unfors RaySafe technical support. Many common questions and issues are addressed here.
R/F low is optimized for low signal levels, typically found during fluoroscopy, behind a phantom. It has a high sensitivity at the cost of a lower bandwidth (0.1 kHz) and should be used at dose rates below approximately 1 mGy/s. R/F high is optimized for higher signal levels and features a higher bandwidth (2.5 kHz). It is typically used before a phantom, and is required for measuring kVp (as opposed to kV).
Dose is basically a property of a point in space, while dose length product (DLP) is dose times a length. When measuring with a 100 mm ionization chamber the following holds true: DLP = (Measured dose in a point and assuming a homogenous field) • (Slice Width). When using the RaySafe Xi CT it is possible to change between Dose and DLP by selecting Dose Unit as Gy or Gycm in the settings menu.
The RaySafe Xi switches to kVp automatically, as soon as the signal level is high enough (but only when using R/F high). For high frequency generators, the difference between kV and kVp is negligible.
The RaySafe Xi R/F or Mammography Detector only measures radiation from one (1) direction, not scattered radiation from behind, because the back of the detector is shielded with 1 mm of lead. The detector may therefore be placed on any surface and still measure true air kerma. Most ionization chambers measure primary as well as scattered radiation, which is why they should be placed free in air (at least 0.5 m (2 ft) from any scattering material). When used in such fashion, the RaySafe Xi will show similar readings when compared to an ion chamber.
The setting is to be able to measure accurate kV with and without the compression paddle in the field. This setting selects between two different kV calibrations. It does not affect any other measurement, such as dose, HVL or time.
As far as we know, all mammography devices have at least one of the above mentioned beam qualities. It is enough to measure kV for one (1) beam quality on each machine since the true kV is the kV over the x-ray tube and not the result in the x-ray beam after filtration. To calibrate the RaySafe Xi for measuring kV on other beam qualities would thus result in unnecessary complexity and a higher calibration cost.
The RaySafe Xi will not show any mAs readings. As long as the mAs cable is securely connected to both generator and base unit (in any polarity), there is no increased risk of damaging the generator or the Xi.
Please charge the battery, see chapter Getting Started in your Xi Manual.
Make sure that all cables are properly connected and that you have:
• If using Bluetooth, established a Bluetooth connection (password 1234).
• If using serial cable or USB/Serial adapter, select the correct COM port in file/settings menu of RaySafe Xi View.
• press the RaySafe Xi View Communication Start button.
If you are measuring on a generator with AC signal on the mAs measurement point, you will need a rectifier (optional) to get correct values. Contact Unfors Technical Support.
This means that the ionization chamber current fails to reach a stable level when the instrument is turned on. Please make sure that:
• the chamber is not irradiated during stabilization or zero adjust.
• you are not operating the instrument outside its specified temperature range. If the problem persists, your instrument might be in need of a repair. Please contact Unfors Service department.
Make sure that:
• you are not operating the instrument outside its specified temperature limits.
• you are not irradiating the detector during the zero adjust phase (when values on display are blinking). When used with pulsed sources it may be necessary to select a longer Calc. delay to avoid end trig and zero adjust during the measurement (see also next problem).
Make sure to select an appropriate Calc. delay if using the instrument with pulsed generators, or with generators having a pre-pulse before the main exposure. The Calc. delay is the time the Xi will wait after radiation before finishing the measurement.
Try the reset switch and make sure that the battery is charged. The reset switch may be found on the LEFT side of your Xi Base unit by accessing the small, unlabeled hole adjacent to the Serial cable. Gently insert the exposed end of a paper clip into the aperture ONE TIME. The Xi Will turn OFF, and reset. Please press the ON key on your Xi front panel to reactivate the Xi.
Make sure that the instrument was connected to the generator during "Zero Adjust" *
• is operating on battery (no AC adaptor). *
• is not connected to a grounded computer (use Bluetooth or a laptop running on batteries with no Ethernet cable connected).
* = Valid for Xi Platinum and older generations of Xi manufactured before February 2011. Not valid from Xi Platinum Plus.
If the illuminance sensor is dirty, please clean it using a slightly dampened cloth. If the problem persists, contact Unfors Service Department.
Please make sure that the true thickness of your Al filters is accurately known and used in the calculation. A resolution in the order of 1 µm is needed for 0.1 mm thickness. Filters should be 0.999 purity.
Is your detector plugged into the Xi Base with the mini USB cable? Try exchanging the short cable for the long cable (or vice versa) Your Xi may require service. Contact customer Service.
Certain x-ray generators (notably the GE AMX4+) have a low high voltage ripple frequency and a variable amplitude of the ripple. To get as accurate result as possible make sure the Xi detector get as much signal as possible. Many mobile x-ray systems have a fixed mA so it is not possible to increase dose rate by the settings. Place your Xi Detector closer to the collimator of the AMX4+ (or similar unit), and redo the exposure with the RF High detector choice.
1. For general radiography, place the detector approximately 50 cm (~20") from the focal spot of the x-ray tube), perpendicular to the length of the tube. Using the light field, (10 cm x 10 cm) center the detector in the beam. Make certain the detector outlines are facing the x-ray beam.
2. For mammography, place the center of the MAM detector centered 6 cm ( 2 3/8") from the chest wall side. Make certain the detector cable is directed to the REAR, away from the chest wall side.
3. For CT kV, place the Xi detector in ISO-center on the table with the R/F-high sensor area aligned with the laser beam symbolizing the x-ray beam. Select a beam width that will cover the sensor area with a couple of mm on each side. Use a high mA >200 and select R/F-high on the Xi. Make exposure with the tube fixed in top position and without table movement.
Your Xi must have mAs capability. A simple check is to look on the Right Side of your Xi for the mAs socket. Your Xi should be operating on its internal battery to make mAs measurements*. DO NOT USE THE WALL CHARGER*. Connect your Xi to the mAs socket of the x-ray generator with the supplied cable. Remove the jumper between the POS & NEG terminals on your generator. Turn your Xi ON. Make an exposure.
IMPORTANT NOTE: If recording data in XiView, your computer MUST be isolated from the AC power. Either use the Bluetooth wireless link (between the Xi and Computer) or use your laptop's internal battery if your Xi is wired to your laptop. Remove mAs cable and reconnect the jumper when completed.
Yes. Set your Xi RF detector in the x-ray beam, with your mAs cable attached. When the Xi RF detector is exposed, it will trigger mAs measurements.
The CT probe is an ion chamber, intended for dose measurements only. It cannot measure kV.
Turn your Xi base OFF. Set your CT probe on a level surface, and do not touch or move the CT probe. Turn your Xi base back ON. If the "Stabilizing" message does not disappear within 1-2 minutes, contact customer service. Your CT probe may need to be returned for service.
Make certain ONLY the black ion chamber portion of the probe is exposed to radiation. Exposing the white base portion can result in wrong readings.
1. Make certain the Xi is turned ON.
2. Make certain the Auto Power Off time is adequate. Your Xi may be turning itself OFF.
3. Make certain your battery is charged. If Battery voltage is LOW, please plug in charger.
4. Make sure you have the proper detector selected. (Mam for mammo, RF for Radioscopic or fluoroscopic procedures).
5. Make certain your detector is plugged in (IS there a 'No detector connected' message?).
6. Make cerrtain your detector is facing the x-ray source
7. Make certain your collimator blades are OPEN.
8. Make certain your detector is positioned properly according to the quick guide.
9. If you are making a mA, mAs, or mAs/combo measurement, swap the polarity of your mA cables on the generator.
10. If you have made a mA or mAs measurement, make certain the mAs jumper is reconnected in the x-ray generator.
11. Make certain your x-ray unit under test is operational.
12. Move the Xi detector closer to the radiation source.
If using PMMA, Al or other added filtration in the beam please remove the added filtration. kV is best measured with no added filtration. For mammography see manual for how to measure best kV for each beam quality.
The latest version of Xi Platinum (5.x and above) automatically corrects for the AMX4+ waveform when calculating kVp.
CRC error means that part of the data has been lost or altered in transit. This could happen if one operates the Bluetooth close to its maximum range, or if there is something interfering with the Bluetooth. Try moving the base unit closer to the computer.
On single phase units, One has to make sure to use RF High at a signal level well above 1mGy/s. Make sure the signal level is high enough to get a KVp reading instead of only kV by moving the Xi detector closer to the x-ray source.
The only calculation needed is the normal calculation for CTDI. (CTDI = [measured value in mGy]*10/4[cm]). Correction for air pressure and temperature is automatically applied to the reading before display.
This could be caused by not having a long enough calc delay when making an exposure. If this does not solve your problem try using another cable.
Display Code: ***
Measurement has started
Display Code: - - -
No value can be calculated
Display Code: < 1 ms
Les than 1 ms valid samples
Display Code: LoSignal
The dose rate is too low to calculate a value (Increase mA or move closer to x-ray source)
Display Code: HiSignal
The dose rate is too high to calculate a value (Increase FDD or decrease mA)
Display Code: LoRange
Calculated kV is less than specified range
Display Code: HiRange
Calculated kV has exceeded specified range
Display Code: t < delay
The exposure time is not long enough to calculate a value. If applicable set trig delay to 0.
Display Code: Ofl.
Overflow, i.e. calculated value is numerically higher than can be displayed.
Display Code: Auto range out of order
At least one of the measuring ranges is out of order.
Display Code: Zero adjust out of range
Hardware offset levels may be out of range due to extreme temperatures.
This can happen if exposure is made during Zero adjust.
Display Code: Offset out of range
Ionization chamber current fails to reach a stable level when the RaySafe Xi CT Detector is turned on.
Display Code: Battery down
The battery must be charged before any measurements can be made.
It is enough to attach the power adapter and let it charge for a minute before trying again and measure with attached power adapter.
Display Code: Detector is incompatible
The version of the connected detector is not compatible with the RaySafe Xi Base Unit version.