3B 8001223 Ultrasonic Computer Tomography Instructions
- June 6, 2024
- 3B
Table of Contents
UE9020200 ULTRASONIC
COMPUTER TOMOGRAPHY
8001223 Ultrasonic Computer Tomography
EXPERIMENT PROCEDURE
- Record an ultrasonic CT image.
- Analyze different measuring parameters.
- Investigate the influence of filtering and image processing.
OBJECTIVE
Investigate the formation of an ultrasonic CT image and its relevant
parameters
SUMMARY
The several steps of the formation of a computed tomography are
illustrated. The difference between damping and sound velocity as measuring
parameters is analyzed. The influence of filtering and image processing is
investigated.
REQUIRED APPARATUS
| Quantity | Description | Item Number |
|---|---|---|
| 1 | Ultrasonic Echoscope GS200 | 1018616 |
| 1 | CT Controller | 1017783 |
| 1 | CT Scanner | 1017782 |
| 1 | CT Measuring Trough | 1017785 |
| 1 | CT Sample | 1017784 |
| 2 | Ultrasonic Probe 2MHz GS200 | 1018618 |
| 1 | Ultrasonic Coupling Gel | 1008575 |
BASIC PRINCIPLE
Xray CT, MRT and PET are computer-aided imaging methods used in medical
diagnostics, industry and research. Processes such as radiation absorption,
nuclear magnetic resonance or particle emission are used to produce cross-
sectional images by means of
appropriately measurable physical quantities. Ultrasonic computer tomography
is another CT method. It differs from X-ray CT in that instead of the
attenuation of X-rays, the attenuation and times of flight of ultrasonic
signals in the test object are measured. With the ultrasonic CT, line scans
are recorded at different angles and put together to form a cross-sectional
image. In this process, the sample arranged between transmission and receiving
probe is moved and turned under computer control. The overlaying of the
projections of individual scans can be followed step by step on the PC.
To form the image the attenuation of sound and the sound velocity are
utilized. The attenuation coefficient of sound p results from the measured
amplitude A and the amplitude without sample A, after the law of attenuation:
(1) For the generation of the sound velocity tomogram the time of flight is
used as the measuring quantity and the following is valid:
(2)
where tο, is the measured time of flight without the sample (the path length s
is constant).
The sample (damping or velocity sample) is attached to the sample holder and
by means of the scanner control is positioned exactly between the two sensors.
Then the sample holder is moved half of the scanning way, the accuracy of
scanning and the number of angle intervals are adjusted and the CT scan is
started. During the measure-ments the individual line scans are observed and
the generation of the tomograms by superposition of the projections of line
scans is studied.
The resulting images are optimized by means of various filters and by
brightness and contrast adjustments, then the damping tomogram is compared
with the velocity tomogram.
EVALUATION
The transmission signal (the diagram left above in Fig. 1) has been measured
with regard to maximal amplitude and time of flight of the maximal amplitude
and from this a line profile (scan at one angle, 500 p.m point distance) has
been built (diagram left below). The superposition by means of the CT-
algorithm (25 angle intervals) yields for sound attenuation to the image left
above (non filtered, contrast changed) and for the sound velocity to the image
right above (also non filtered, contrast changed). Filtering the attenuation
image improves the contrast so the edges become visible (reflection losses).
The inner part hardly distinguishes from the surrounding water, in the sound
velocity image (right) the sample and the inclu-sion are clearly visible as
homogeneous regions of a different sound velocity.
MEDICAL PHYSICS
ULTRASOUND
Ultrasonic Computer Tomography