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I was asked to estimate the skin dose from an 18F extravasation. I'm sure it won't be the last request, so I'm trying to figure out a procedure. The total activity measured in a test syringe images is 35% less than the actual activity. </div>
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<div dir="ltr"><div dir="ltr"><div>I was asked to estimate the skin dose from an 18F extravasation. I'm sure it won't be the last request, so I'm trying to figure out a procedure. <span style="background-color:transparent">The total activity measured in a test syringe images is 35% less than the actual activity. </span><span style="background-color:transparent">I'm not </span>sure <span style="background-color:transparent">how accurate this measurement </span>should<span style="background-color:transparent"> be and would appreciate any expert guidance. </span></div><div><br></div><div>I plan to measure the total extravasated activity from the patient images to enter into the University of Texas (UT) <a href="https://urldefense.com/v3/__https://gsm.utmck.edu/research/MITRP/RIDE.cfm__;!!KGKeukY!1HslGXroK0I59G3ELoPBWs_YPsCABLNSpFxijIaXWrVSZeKDG1oPLruW694Q5IMWtQ2oejbOI757ItX-nUU3rczSG3ad6RcgbKAOUg$" target="_blank">Radiopharmaceutical Infiltration Dosimetry Estimate (RIDE)</a> Tool. To verify my method for measuring total activity, I tested the process on images of a syringe with known activity. </div><div><br></div><div><div>The test syringe (9.07-mCi at start time) was scanned with a single 2-minute bed on a Canon Cartesion Prime. Reconstruction was done with PSF, TOF 3D OSEM. The images were corrected for decay (start time), randoms (delayed), attenuation (CT), and scatter (MISE). <span style="background-color:transparent">I'm using ImageJ to open the DICOM images.</span><span style="background-color:transparent"> I used Z-Project... to <u>sum</u> all of the images then multiplied the mean of the summed image by the total volume to get 5.9 mCi. </span></div></div><div><span style="background-color:transparent"><br></span></div><div><div><div><span style="background-color:transparent">I expect individual pixels to be underestimated due to the partial volume effect, but I assume the total activity should be immune to that. </span><span style="background-color:transparent">Is my assumption wrong? Can one of the corrections be inappropriate (scatter or randoms?) for such a small, concentrated source? Or is a 35% underestimate within the expected range for total activity? </span><span style="background-color:transparent">Or is it likely an error in my calculations?</span><span style="background-color:transparent"> </span></div></div><div><div><br></div><div>If anyone on the list has experience making these measurements from DICOM images, would you be willing to share some tips or help me understand what I'm missing? If anyone responds directly, I'll gladly follow up with the list when we have a final answer.</div><div><div></div></div><br class="gmail-Apple-interchange-newline"></div></div><div><span style="background-color:transparent">Thanks in advance!</span></div><div><span style="background-color:transparent">Adam</span></div><div><span style="background-color:transparent"><br></span></div><div><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr">===============================================<br>Adam C. Springer, MS, <a href="https://urldefense.com/v3/__https://myabr.theabr.org/*/certificate-public-reporting/P5911__;Iw!!KGKeukY!1HslGXroK0I59G3ELoPBWs_YPsCABLNSpFxijIaXWrVSZeKDG1oPLruW694Q5IMWtQ2oejbOI757ItX-nUU3rczSG3ad6RfCrUYMTA$" target="_blank">DABR®</a>, <a href="https://urldefense.com/v3/__https://www.absnm.org/certification-verification.html*/certificate-public-reporting/ABSNM-2026-09__;Iw!!KGKeukY!1HslGXroK0I59G3ELoPBWs_YPsCABLNSpFxijIaXWrVSZeKDG1oPLruW694Q5IMWtQ2oejbOI757ItX-nUU3rczSG3ad6RcWkvIX2A$" target="_blank">DABSNM</a>, <a href="https://urldefense.com/v3/__https://ibmrs.org/abmrs-credential-search-global/__;!!KGKeukY!1HslGXroK0I59G3ELoPBWs_YPsCABLNSpFxijIaXWrVSZeKDG1oPLruW694Q5IMWtQ2oejbOI757ItX-nUU3rczSG3ad6Rd2vo3Cxg$" target="_blank">MRSE</a> (MRSC<span style="font-size:12pt;line-height:115%;font-family:"Aptos Light",sans-serif">™</span>)<br>Medical Physicist & CEO<div>KLS Physics Group, LLC<br>PO Box 700<br>Ruston, LA 71273<br>Office: <a href="tel:(318)%20255-5033" value="+13182555033" target="_blank">318-255-5033</a><br>Mobile: <a href="tel:(318)%20272-8292" value="+13182728292" target="_blank">318-272-8292</a><br><br><br></div></div></div></div></div>
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