SA Imaging Provides Higher Resolution Medical Images
1. Synthetic Aperture Imaging
Medical Imaging Computing Systems Lab
Department of Electronic Engineering
Interdisciplinary Program of Integrated Biotechnology
Medical Solutions Institute
Sogang University, Seoul, Korea
Medical Imaging Computing System1 Lab
s
2. Contents
Introduction
Method
– Synthetic aperture imaging techniques
– Evaluation metrics
Result and discussion
– Phantom study
– In vivo study
Conclusion
Further works
Medical Imaging Computing Systems Lab
3. Introduction
Transmit beam
Receive beam
Tx/Rx beam
One way dynamic focusing Two way dynamic focusing
Fixed Tx focusing / Dynamic Rx focusing Dynamic Tx and Rx focusing
Synthetic aperture imaging
Medical Imaging Computing Systems Lab
4. Introduction
Conventional imaging SA imaging
Transmit focusing
Receive focusing Low resolution
images
∑ ∑
Reconstructed
image
Low resolution image High resolution image
Medical Imaging Computing Systems Lab
5. Method : Synthetic Aperture Imaging Technique
Single element transmit Defocusing BiPBF
SA with a virtual
Single element transmit Defocusing
source (BiPBF)
No decrease of acoustic No decrease of acoustic
Advantage -
power power
Number of synthesize
Low signal to noise Need for adjusting transmit
Disadvantage ratio(SNR) beamforming
beams need to be adjusted
depending on depth
Medical Imaging Computing Systems Lab
6. Method : SA with a Virtual Source
Synthetic aperture imaging technique with a virtual source element
– Regard transmit focal point as a virtual source
– Spherical waves are propagated back and forth from the virtual source
– Tx delay : – Rx delay :
Transmit wave-fronts model with Principle of transmit synthetic
two virtual source located at each focusing
transmit focal point with the virtual source
Medical Imaging Computing Systems Lab
9. Result and Discussion : Phantom Study
6-dB lateral resolutions
– 6-dB lateral resolutions at each wire target
– Conventional and MZTF methods
• Best lateral resolution at the each transmit focal depth
• Broadened as imaging distance from the focal depth was increased
– SA method
• Uniform lateral resolution
Medical Imaging Computing Systems Lab
10. Result and Discussion : Phantom Study
SNR
– SNR along the depth obtained from three methods
– Conventional and MZTF methods
• The high SNR was achieved only at the focal depth
– SA method
• Mean SNR value was improved
Medical Imaging Computing Systems Lab
11. Result and Discussion : Phantom Study
CNR, SNR
Conventional MZTF SA
CNR 3.1 3.4 3.4
SNRmean 15.3 dB 16.7 dB 23.6 dB
– Higher CNR value in SA method than
conventional method
• Reduced speckle size in the SA method due to the
enhanced lateral resolution → higher CNR ROI of CNR
– CNR value was the same in SA method and
MZTF method
• ROI for CNR measurement was located at one of
transmit focal depth
Medical Imaging Computing Systems Lab
12. Result and Discussion : Phantom Study
Penetration depth
Filtered intensities of echo and noise signal used for
measuring the penetration depth
Visible
ROI of
penetration depth The penetration depth along
the number of sub-aperture (M) of SA method
Medical Imaging Computing Systems Lab
13. Result and Discussion : In-vivo study
In-vivo data acquisition set-up
– Patients were scanned in supine position by an experienced radiologist
– The patients with benign and malignant tumors
– Two sets of RF data from each patient were acquired sequentially for the
conventional and SA imaging
– Focus point
• Conventional : adaptive
• SA imaging : 40 mm
Common improvement
– Conspicuity and margin sharpness of the lesion is improved
– Higher contrast resolution
– Increase of resolution in deep portion
Medical Imaging Computing Systems Lab
14. Result and Discussion : In-vivo study
B-mode in-vivo images
– Malignant infiltration ductal carcinoma
• Edge shadowing artifacts has been dramatically reduced in the SA image (white arrows)
• Resolution in deeper portion has decreased (white dotted box)
Medical Imaging Computing Systems Lab
15. Conclusion
Assessed conventional and SA image
– Quantitative evaluation
• SA images provided higher CNR and SNR values
• SA images provided uniform improvement in image resolution at all
points (two-way dynamic focusing)
• SA images provided better penetration depth
– Qualitative evaluation
• SA images provided higher lesion conspicuity and global preference
– Consistent result with both in-vivo and in-vitro data
Medical Imaging Computing Systems Lab
