Performing a Sectorial Scan Sensitivity/ Velocity/Wedge Delay Calibration-Shear Wave PA Using SDHs at Known Depths 2.0 SW By Nick Bublitz Calibrations-Required items Calibration block with 2 same size reflectors at known depths- (Navships block with SDHs or other calibration block with 2 same size reflectors at known depths) Couplant-water works best for practiceotherwise whatever you will test with Guide to keep from skewing- use a ruler, set the block on its side, or on IHC wedges can screw down one sides carbide pins. 2 Velocity Calibration The velocity calibration will fine tune the velocity to that of the calibration block. It will require two reflectors of the same size at two different known depths (Depth). A radius may also be used in sound path overlay (Radius) . In many cases the default material velocity and wave type set by the operator in the group wizard is sufficient and this calibration can be skipped because wedge delay will adjust accordingly to allow accurate measurements in the depth axis. If performed the velocity calibration should be done before the wedge delay calibration. Performing a velocity calibration after wedge delay will remove the wedge delay calibration. 3 UT the velocity calibration will calculate the time difference to two reflectors of known depth or sound path and calculate a material velocity.Velocity Calibration Just like Con. in PA we often use true depth rulers so a Navships 4 works well (depth) . Many conventional users use an IIW block (radius). Select Velocity Calibration Go to the WizardCalibration menu Select Ultrasound and Velocity Start the wizard 5 . Choose an angle near the middle of your angle sweep using the angle function. 6 . The calibration will utilize a single beam as the velocity will be consistent across all the angles. Adjust range as needed to ensure you will see the 2 reflectors you have chosen.Select A-Scan Put the probe on your block over the first reflector. Set Depth 1 and 2 Select depth from echo type Set depth 1 and depth 2 to your reflector depths. 7 . Set Gate A on Depth 1 Move probe back and forth over the first reflector building an envelope. Use a guide so you do not skew right or left. Get position. 8 . Ensure you peak the reflector. Adjust the gate to encompass the reflector. 9 . Adjust the gate to encompass this reflector. Get position.Set Gate A on Depth 2 Repeat the peaking process on your second reflector. 10 .Accept or Restart View the velocity determination If it is sensible accept the calibration. Wedge delay calibration will compensate for this. if not restart. Depth readings may not be 100% accurate after a velocity calibration at all angles due to the different wedge path distance of individual beams. 11 . Code compliance relies heavily on the ability to calibrate each beam. After wedge calibrations. Wedge delay needs only 1 distinct reflector -a known depth reflector (depth) will be used here. It is a critical calibration to ensure reflector depth/Thickness/TOF is accurately measured at every angle as well as for accurate measurements of through wall height etc. accurate depth (DA etc) and surface distance (PA etc) measurements can be taken. Induced wear on the wedge will also be accounted for if it is not to severe to prohibit calibration. A single radius in sound path could also be used. For efficient and effective setups it is crucial that this is done with a software tool to speed up the process and minimize human error. Because of the multiple beams at varying angles it is critical that any PA instrument has a method to calibrate each beam for wedge delay.Wedge Delay-Depth Reflector Wedge Delay will enter compensation for the varying distance of travel of the beams through the wedge medium and account for the various exit points. Tolerance is reference only.Wedge Delay Calibration-Depth Enter the calibration menu Select Ultrasound and Wedge Delay-Start Select depth and input depth to the reflector and a tolerance. it does not affect the quality of the calibration. 12 . Set Section Decide if you want to calibrate the whole angular sweep or break it up into separate calibrationsfor most setups with a good calibration block you can calibrate the whole sweep. Hit Next 13 . Move the probe forward and backwards to ensure gate is encompassing reflector through all angles and there are no other reflectors that will affect calibration.Set Gate A on Depth A Put the probe on the block so you can see the chosen depth reflector. Adjust the gate start/width/threshold to encompass the reflector. 14 . 15 . Adjust gain as needed. Move in both directions until the green line is built across the whole angular range. Hit calibrate.Calibrate and Accept Move the probe forward and backward applying even pressure and avoiding skewing right or left. 16 .Accept or Restart After hitting calibratererun the probe through the angular range verifying you are within the set tolerance. Accept or Restart. Verifying Wedge Delay Set the DA reading from the MeasurementReadings menu Turn on the Highest % feature in the DisplayProperties-Source menu Run the probe through the angular sweep while observing the DA reading. The Omniscan will track the highest reflector in the red gate. Return the source to normal before next calibration! 17 . Calibration reflector and natural flaw response relies heavily on angle so it is critical each beam/angle can be calibrated to the same sensitivity level. This will insure no matter what angle the reflector is seen at the % FSH is the same for rejection or detection purposes as well as for the amplitude based color coded imaging selections. 18 .Sensitivity Calibrations Sensitivity calibrations equalize the sensitivity (amplitude) to a given reflector through all the angles. one 2. The default tolerance of 5% will show two lines – one 2.5% below.Sensitivity Calibration Enter Calibration menu and select Sensitivity Choose a reference screen height to equalize sensitivity to (80% FSH) and a tolerance.5% above your set reference. 19 . This does not affect the quality of the calibration it is merely visual reference. Getting Started Choose a SDH and couple your probe above it Use a guide system to keep the probe from skewing side to side. 20 . Set Section Choose whether to calibrate the whole angular sweep in one step or break it up into separate calibrationsif your calibration block has adequate spacing between SDHs you can usually do the whole range. 21 . Move the probe forward and backward to ensure the gate covers the reflector through all the angles and there is not on any other reflectors that may inhibit the calibration 22 .Set Gate A on Echo A Set the gate to encompass the SDH reflection. Adjust the start/width/threshold of the gate. 23 .Set Compensation Gain Allows you to adjust the gain as needed to ensure the reflector is seen properly throughout all the angles In most cases no adjustment or an adjustment of the overall gain (if over reference level FSH%) is needed. move the probe forward and backwards to build the green line as the reflector is seen by the angles.Calibrate and Accept Applying even pressure and not skewing right or left. Ensure the green line is on-screen across the whole screen-not to low or over the tolerance lines. 24 . 25 .Calibrate and Accept Press Calibrate Verify the calibration by repeating the forward and backward movement of the probe The green line should fall within the defined tolerance lines across all the angles. Accept or Recalibrate as needed. To Verify Sensitivity Calibration To verify sensitivity go to Display menu Select properties Change source to Highest Run the probe back and forth and observe FSH in the A% reading field as the data cursor tracks the highest amplitude signal in the red gate. Return the source to normal before further calibrations! 26 . it is a tendency for con.General Tips for Calibrations-Omniscan-General Even pressure and couplant are key. looking for interfering reflectors. ut operators to look at only the a-scanremember this is only one angle in a sweep. A guide will ensure sure the same portion of the beam sees the reflector –this is key The Omniscan must see the natural state (building of green line) between about 10% FSH and the high tolerance set. If the green line drops off suddenly examine your a-scan at the point it drops. Utilize the scan view for setting gates.practice makes perfect. rebuild green line and hit calibrate again. 10% FSH max tolerance line 27 .the Navships block is a great block for PA calibrations. Tighter spacing of reflectors may require breaking up the calibrations into two or more sections using the set section feature to keep other reflectors from entering the gated tracking area. your gate threshold and/or width may need adjustment. Instead of restarting calibrations you can reduce gain. A good calibration block helps a lot. Practice with water-it doesn’t shovel like gel couplant. Sluggish-low PRF.ensure gates are all on screen and minimized.General Tips for Calibrations-Omniscan settings Ensure the tracking function is set to No db ref ( ) normal-Display-Properties-Sourceprf Normal. since the wizards use a tracking system Highest/Thinnest/All Laws can interfere Make sure you are set to run off the clock of the Omniscan. 28 x: sec . not an encoder base-Scan-Inspection-Scan-Time-look in right hand corner-should be in seconds.Ut settings-Advanced-db Ref-Off look in left hand corner These are all set ok by default but if you create a setup and have issues these are key places to look. minimize range etc All of the above usually result in no green line at all of a very sluggish jerky tracking response. Make sure db reference is off. use a guide and apply even couplant between wedge and block. a 60 degree wedge will be easier calibrated at 72 degrees.adjust gain.longer beam paths (higher angles) will thus have more gain added to facilitate proper calibration.hold probe with even pressure.General Tips for Calibrations-Omniscan Rounded irregular hills in green lineusually due to uneven pressure or skewing left/right. 29 . Lower wedge angles will be easier “bent” to low angles. the opposite for higher – a 45 degree wedge is easier to calibrate at 30 degrees. 55 degree wedge is a good wedge for both extremes. Gain will add an amount of gain per us of travel. Green line not able to be set between reference and 10% for training. also excess couplant in that area. reduce angular sweep or change wedge. gain. use comp. Comp. reapply couplant here.view ascan at point of dropout.General Tips for Calibrations-Omniscan Sharp jagged triangular “dropouts” in green line trace. Can also be gating-look at scan to set gates over the entirety of the reflector through all the angles.usually couplant dependant.complete loss of couplant or insufficient amplitude. increase gain.if it repeats at the same angle every time after reapplying couplant.reapply couplant. it is more than likely between the wedge and probe. lower gate threshold to encompass ascan amplitude. Sharp diagonal dropout.check couplant between wedge and block first. 30 . consult a technical support specialist or database of wedge parameters.General Tips for Calibrations-Omniscan Data cursor tracks to other reflector not being used for calibrationexamine and reposition gate.Probe/Part-Wedgecheck if proper wedge is selected and note the wedge settingsespecially height.if everything else fails. 31 . use calibrate by section feature. use different block.the reflector should not drift in depth dramatically.if it does there is probably an error in the wedge file parameter. observe a single reflector in a true depth scan. Unable to perform wedge delay or improper wedge delay. Calibrate by Section 32 . Reduce gain until all beams fall below the high tolerance line but still above about 10% FSH.green line may appear to go to edges. Wedge delay calibration cannot be performed. The calibration cannot be performed” (sensitivity calibration) -at least one angle or vpa is greater than the reference amplitude you set. –at least one angle or vpa is not being picked up due to low amplitudeincrease gain.Omniscan Error Messages during CalibrationSensitivity -“At least one context has an amplitude peak greater than 100%. make sure you run the white trace line completely off screen and beyond. 33 .”.The calibration cannot be performed” or “At least one context has no amplitude peak in gate A. -”at least one context has an amplitude peak of 0%. troubleshoot couplant etc as needed Other cause of the above two errors-not completing the edges (first/last angles/ vpas).
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Report "2.a.omniscan Setup - Calibration for Sectorial Scan"