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Re: Mamm focal spot
>Date: Fri, 5 Jun 1998 11:17:21 -0600
>Reply-To: Medical Physics Mailing List <MEDPHYS@LISTS.WAYNE.EDU>
>Sender: Medical Physics Listserver <medphys@lists.wayne.edu>
>From: "Joel E. Gray, Ph.D." <joelgray@M3.SPRYNET.COM>
>Subject: Re: Mamm focal spot
>To: MEDPHYS@LISTS.WAYNE.EDU
>
>Ann,
>
>Interesting problem!! When you calculated the size from the slit image did
>you take into account the tube tilt angle? This can make a difference of
>30 to 50%--and I am not sure of the tilt on the UC.
>
>The important issue is image quality, not the size of the focal spot. If
>you measure resolutions specified in the ACR Manual, i.e., 13 c/mm parallel
>to the anode-cathode axis and 11 c/mm perpendicular, then the image quality
>should be adequate (especially since this is a measure of system resolution
>if you do it as specified by ACR).
>
>Both the size and the distribution of the focal spot are important. The
>distribution can make a difference of 2 or greater in the resolution. A
>gaussian distribution has far better resolution that a uniform distribution
>and a dual peaked distribution has about half the resolution as a uniform
>distribution.
>
>Bottom line-- if you meet the ACR resolution criteria then I would accept
>the x-ray tube!
>
> Joel
>
>Joel E. Gray, Ph.D., Consultant
>2804 Second Street SW, Suite 334
>Rochester, Minnesota 55902
>
>Ph 507-286-8910
>Cell Ph 507-269-4247
>Fax 507-286-8910
>e-mail joelgray@m3.sprynet.com
>
>
>
>
>
>
>
>
>>Hi
>>The focal spot sizes of 3 different Philips Diagnost
>>UC Mammographic x-ray machines were evaluated using a slit camera
>>and star pattern. The calculated focal spot sizes were greater than
>>the 1.5 x nominal size specified by ACR.
>>Using a Du Pont/Ackerman phantom or test object, images taken on
>>these machines could resolve 10-12 lp/mm.
>>Do we tell the manufacturer to do something about it or just monitor
>>and see if they deteriorate?
>>We are attempting to establish a type of Mammography accreditation so
>>would like to know what our stand point should be on this aspect.
>> Many thanks
>>Ann Sweetlove
>>Medical Physicist, Bloemfontein, South Africa
>>gnbimas@med.uovs.ac.za
>>
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>>Frequently Asked Questions (FAQ) for Medphys at:
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