Evaluation of single-photon emission computed tomography images obtained with and without copper filter by segmentation.
BACKGROUND
Measurement of accurate attenuation of photon flux in tissue is important to obtain reconstructed images using single-photon emission computed tomography (SPECT). Computed tomography (CT) scanner provides attenuation correction data for SPECT as well as anatomic information for diagnostic purposes. Segmentation is a process of dividing an image into regions having similar properties such as gray level, color, texture, brightness, and contrast. Image segmentation is an important tool for evaluation of medical images. X-ray beam used in CT scan is poly-energetic; therefore, we have used a copper filter to remove the low energy X-rays for obtaining correct attenuation factor. Images obtained with and without filters were quantitatively evaluated by segmentation method to avoid human error.


METHODS
Axial images of AAPM CT phantom were acquired with 3 mm copper filter (low intensity) and without copper filter (high intensity) using low-dose CT (140 kvp and 2.5 mA) of SPECT/CT system (Hawkeye, GE Healthcare). For segmentation Simulated Annealing Based Fuzzy c-means, algorithm is applied. Quantitative measurement of quality is done based on universal image quality index. Further, for the validation of attenuation correction map of filtered CT images, Jaszczak SPECT phantom was filled with 500 MBq of (99m)Tc and SPECT study was acquired. Low dose CT images were acquired for attenuation correction to be used for reconstruction of SPECT images. Another set of CT images were acquired after applying additional 3 mm copper filter. Two sets of axial SPECT images were reconstructed using attenuation map from both the CT images obtained without and with a filter.


CONCLUSIONS
When we applied Simulated Annealing Based Fuzzy c-means segmentation on both the CT images, the CT images with filter shows remarkable improvement and all the six section of the spheres in the Jaszczak SPECT phantom were clearly visualized.
Department of Nuclear Medicine, SGPGIMS, Lucknow, India.
Subhash Chand
SC
Kheruka
Department of Radiotherapy and Radiation Medicine, Institute of Medical Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh, India.
Lalit Mohan
LM
Aggarwal
School of Biomedical Engineering, IIT, Banaras Hindu University, Varanasi, Uttar Pradesh, India.
Neeraj
N
Sharma
Department of Physics, HNB University, Srinagar, Uttarakhand, India.
Umesh Chand
UC
Naithani
Department of Radiotherapy, SGPGIMS, Lucknow, India.
Anil Kumar
AK
Maurya
Department of Nuclear Medicine, SGPGIMS, Lucknow, India.
Sanjay
S
Gambhir
Copper filter; Jaszczak single-photon emission computed tomography phantom; fuzzy c-means; segmentation; single-photon emission computed tomography