ABSTRACT
The relationship between frequency (wavelength) and lateral spatial resolution is given by Equation (3.30). These relationships are graphically illustrated in Figure 8.1 and Figure 8.2. As ultrasound frequency is increased to 50 MHz, an axial resolution and lateral resolution of better than 20 and 100
µ
m for an
f
number of 2.9 can be achieved, respectively. The price to be paid is an increase in attenuation. The effect of attenuation coefficient of a few types of tissues of clinical interest is shown in Figure 8.3. At 50 MHz, the depth of penetration for most tissues would be limited to 4 to 5 mm. As was discussed, the depth of penetration may be increased slightly by introducing novel signal processing methods such as coded excitation; however, the range of frequencies that can be applied to a certain organ is limited.
