Ultrasound and Electromagnetic lab
Biomedical Ultrasound and Electromagnetic lab
FCM based extraction of heart with motion compensation for
accurate estimation of tracer perfusion
To measure the blood flow in different regions of the heart, tracers are used. The tracer is injected in the blood stream that reaches the heart. When the PET scanning is conducted the tracer appears to be of high intensity and other regions appear to be of low intensity. Using this phenomenon the flow of the blood can be measured based on the wash in and wash out curves obtained from tracer intensities. If a region stays dark throughout, it shows that the blood has not reached that part of the heart. During the process of image acquisition different kind of movements induce calculation errors along with the decrease in image resolution. Once you get the complete data, it has to be made sure that you are corresponding same portions of heart in different images taken at different times.
During a beat cycle, heart not only expands and contracts but it also rotates along the axes. To incorporate this motion in the parameter estimation, a compensation technique has to be applied to nullify the effect of these motions. For the rotation along the two axes, instead of calculating a global rotation factor for the alignment along y-axis, different rotation angles are calculated for different time bins. In this way at all times the heart is exactly aligned no matter in which state of a beat cycle it was in. For expansion and contraction, the biggest size is selected at a certain time and all others are interpolated to make the size equal to the biggest one. If this is not done, you can end up comparing a sector of heart with a black portion in any other time bin.
Processing of Data
Once the raw data is acquired, it needs to be processed to extract the heart from all sorts of noise. For that image is passed through the Fuzzy clustering routine that sifts out the major clusters from the image, the heart being one of those.
Once the heart is extracted it is aligned to one of the axes. This is done using the projections on the plane. Due to the elliptical shape of the heart, it can only be aligned to y-axis if its projection on x-axis is smallest. In this way it can be made parallel to y-axis.
The model we are working on is proposed in a paper by Gary Hutchins. It is governed by the following three rate parameters
Using the above model the perfusion parameters are calculated and the maps for all these parameters is shown below.