jim@sniff.tamu.edu (02/28/91)
Hello, I hope that this is the right group to post to. My lab is just getting into working with CT data. We are currently using Sunvision on a Sparcstation 1+. Our CT machine produces 256 x 256, 16 bit images. Some of the problems that we have had is in scaling the data to 8 bits for Sunvsision. We have had some luck in displaying images, but there seems to be some degradation between what the CT machine displays and what we are able to display. Our ultimate goal is 3D volume rendering of stuctures from the CT slices. I am looking for info in the following areas: 1. quanitizing of data from 16 bit to 8 bit (I have seen some info on converting from 24 bit color to 8 bit, but nothing on 16 bit grayscale to 8 bit grayscale) 2. Should we be using the Delta (Housefield) values for the reconstruction and where can I get some info on calulating these values (our radiology department knows how to work the machine, but that is all) Thanks, Jim Snell, DVM, MS Department of Veterinary Anatomy and Public Health From: jim@sniff.tamu.edu (Jim Snell) Newsgroups: comp.graphics Subject: Medical CT scan info Expires: References: Sender: Followup-To: Distribution: usa Organization: Texas Veterinary Medical Center, College Station Keywords: CT, medical, imaging Hello, I hope that this is the right group to post to. My lab is just getting into working with CT data. We are currently using Sunvision on a Sparcstation 1+. Our CT machine produces 256 x 256, 16 bit images. Some of the problems that we have had is in scaling the data to 8 bits for Sunvsision. We have had some luck in displaying images, but there seems to be some degradation between what the CT machine displays and what we are able to display. Our ultimate goal is 3D volume rendering of stuctures from the CT slices. I am looking for info in the following areas: 1. quanitizing of data from 16 bit to 8 bit (I have seen some info on converting from 24 bit color to 8 bit, but nothing on 16 bit grayscale to 8 bit grayscale) 2. Should we be using the Delta (Housefield) values for the reconstruction and where can I get some info on calulating these values (our radiology department knows how to work the machine, but that is all) Thanks, Jim Snell, DVM, MS Department of Veterinary Anatomy and Public Health
rick@hanauma.stanford.edu (Richard Ottolini) (03/01/91)
In article <12803@helios.TAMU.EDU> jim@sniff.tamu.edu writes: > >Hello, > >I hope that this is the right group to post to. > >using Sunvision on a Sparcstation 1+. Our CT machine produces >256 x 256, 16 bit images. Some of the problems that we have had is >in scaling the data to 8 bits for Sunvsision. We have had some luck >in displaying images, but there seems to be some degradation between >what the CT machine displays and what we are able to display. Our Use a non-linear conversion from orignal data to byte integers. One way is to partially sort the data into a histogram and scale the existing range between 0 and 255. Another enhancement is called the gamma contrast enhancement. That is to raise each sample to a fractional power. This can be done by table-lookup at both the conversion time and display time. We use an ad-hoc partial histogram to obtain a reasonable gamma. We compute an upper bound and half intensity value of the data distribution and fit a gamma power to that. For seismic data which is distributed towards zero, we use the 99th and 85th percentile for these two values.