13
Distance
Frequency (MHz)
(cm)
1
3
5
7.5
1
0.9332
0.8128
0.7080
0.5957
2
0.8710
0.6607
0.5012
0.3548
3
0.8128
0.5370
0.3548
0.2113
4
0.7586
0.4365
0.2512
0.1259
5
0.7080
0.3548
0.1778
0.0750
6
0.6607
0.2884
0.1259
0.0447
7
0.6166
0.2344
0.0891
0.0266
8
0.5754
0.1903
0.0631
0.0158
I’=I*RF, where I’ is the intensity in the soft tissue, and I is the time-averaged intensity measured in water.
Tissue model:
Tissue temperature elevation depends on the power, tissue type, beam width, and scanning mode. Six models have been
developed to mimic possible clinical situations.
Thermal model Composition Mode Specification Application
2
TIS
Soft tissue
Unscanned
Large aperture (>
1cm2)
Pencil probe
3
TIS
Soft tissue
Scanned
Evaluated at surface Breast colour
4
TIB
Soft tissue and bone Scanned
Soft tissue on the sur-
face
Muscle colour
5
TIB
Soft tissue and bone Unscanned
Bone in focus
Fetus head
PW
6
TIC
Soft tissue and bone Un-
scanned/scanned
Bone at the surface
Transcranial
Soft tissue:
Describes low-fat-content tissue that does not contain calcifications or large gas-filled spaces.
Scanned: (auto scan)
Refers to the steering of successive bursts through the field of view, e.g. in B and colour mode.
Unscanned:
The emission of ultrasonic pulses occurs along a single line of sight and is unchanged until the transducer is moved to a
new position. For instance, in PW and M mode.
TI:
TI is defined as the ratio of the in-situ acoustic power (W.3) to the acoustic power required to raise the tissue temperature
by 1°C (Wdeg), TI = W.3/Wdeg.
Three TIs were developed for use during different examinations: (TIS) corresponding to abdominal soft tissue; bone
(TIB) for fetal and neonatal skulls; and cranial bone (TIC) for paediatric and adult skulls.
An estimate is needed of the acoustic power in milliwatts necessary to produce a 1°C temperature elevation in soft tis-
sue: