1. TISSUE HARMONIC IMAGING (THI)
SITI AISHAH BINTI SHUIB A141063

2. CONTENT Introduction of Tissue Harmonics Imaging
What are Tissue Harmonics?
Generation of Tissue Harmonics
Artifact Reduction with Tissue Harmonics
Image Formation in Tissue Harmonics
Image Characteristics
Clinical Effects of Tissue Harmonic Imaging

3. INTRODUCTION A new grayscale imaging technique
Images derived from higher frequency that produced second harmonic sound when the ultrasound pulse passes through tissue within the body
Several advantages:
Improved contrast resolution
Reduced noise and clutter
Improved lateral resolution
Reduced slice thickness
Reduced artifacts
Improved signal-to-noise ration

4. WHAT ARE TISSUE HARMONICS?
Harmonics are multiples of the fundamental beam
Transmitting a band of frequencies centered at 2MHz will result in production of harmonic frequency bands at 4 MHz, 6MHz
This doubled frequency sound is called the second harmonic
Only the lowest frequency harmonic is used to form images
Higher order harmonics not used in image formation because of:
Range of frequencies can detect is insufficiently large to capture these higher frequency signals
It is progressively lower in amplitude
More quickly lost as they pass through tissue

5. GENERATION OF TISSUE HARMONICS
The peaks and troughs of the transmit pulse
Tissue alternatively expand and contract, distorting its shape
Tissue density increase causing the peak of the sound wave to travel slightly faster than the trough
Result: non-linear propagation, the wave become progressively more asymmetrical
The asymmetrical distortion result in harmonics

6. Continue…
As ultrasound wave travels trough more tissues, more harmonics are generated
The production of harmonics is proportional to the square of the fundamental intensity
Harmonics are generated predominantly by the the main transmit beam
The maximal production of harmonics is at the focal zone
Beam formed from tissue harmonics signals have less side lobes, less noise, and improved contrast resolution.

7. ARTIFACT REDUCTION WITH TISSUE HARMONICS
Exhibit a reduction in image noise and clutter with improvement in contrast resolution (improved signal-to-noise)
Reduce artifact in several ways
- Tissue harmonic signals produced in the tissue only pass through the body wall one time.
Decrease scatter from the body wall
- Harmonic imaging prefers reject echoes that come from weak parts of the beam (side lobe, reverberation)
Reduced artifacts from weak echoes
- The virtual elimination of reverberation artifacts from the body wall
Less near field haze from body wall reverberation

8. IMAGE FORMATION IN TISSUE HARMONICS
Techniques to detect harmonics and eliminate the unwanted fundamental echoes:
Filtration
Single Line Pulse Inversion
Side-by-side Phase Cancellation
Pulse Encoding
Tissue harmonic imaging operates by transmitting a fundamental beam that has a lower frequency
As it propagates through tissue inside the body, generates the higher frequency harmonic sound
Echoes from the fundamental frequency are rejected.

9. Continue.. Single Line Pulse Inversion (PI) Filtration
Temporal cancellation technique
Adds the echoes from two opposite polarity pulse to cancel the fundamental echoes, leaving only the harmonic information
Filtration
Remove echoes from the fundamental frequency and allow the harmonic frequency to pass
Side-by-side cancellation
Spatial cancellation technique
Sends both signals together at the same time with opposite phases
Pulse Encoding
Relatively complex sequences to give each a unique code
Recognized by special decoder
Useful in the near field

10. TISSUE HARMONIC Artifacts Decreases Image Dynamic Range
Image Characteristics
Decreases Image Dynamic Range
- Amplitude of the harmonic signal is lower in magnitude than the fundamental signal because of dynamic range of harmonic imaging is lower than the fundamental beam.
- It results in images with more contrast, improve visualization.
Better Lateral Resolution – Reduced Slice Thickness
- Slice thickness of harmonic frequencies is narrower than the fundamental pulse
- The edges of any ultrasound beam produce fewer harmonics than central beam
Artifacts
- Reduces some detrimental artifacts while useful artifacts are made more visible
- Square law in harmonic imaging, harmonic production is propotional to the square of the fundamental amplitude
- Results in minimizing certain artifacts -
Worse Images in ‘Glass Body’ Patient
- The resolution in harmonic images may be worse than fundamental imaging due to filtration decrease bandwidth
- Related to the better contrast resolution of the higher frequency fundamental image

11. CLINICAL EFFECTS OF TISSUE HARMONIC IMAGING
Display pathology and normal structures
Decrease the time required to scan some patient
Lead to important clinical information
Identify lesions that are invisible or nearly invisible
Confidently diagnose renal cell carcinoma and kidney stone
Reducing the need for follow-up CT exams
Easier to obtain better quality images
Improve the overall quality of ultrasound diagnosis

12. REFERENCE
Philip W. Ralls M.D. Tissue Harmonic Imaging-Updated. 2004

13. THANK YOU 