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In table 1, a comparison between different frequencies on bone is made. Which is better, a higher or lower frequency?

In table 1, a comparison between different frequencies on bone is made. Which is better, a higher or lower frequency?

Elements Of Electromagnetics
Elements Of Electromagnetics
7th Edition
ISBN:9780190698614
Author:Sadiku, Matthew N. O.
Publisher:Sadiku, Matthew N. O.
ChapterMA: Math Assessment
Section: Chapter Questions
Problem 1.1MA
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In table 1, a comparison between different frequencies on bone is made. Which is better, a higher or lower frequency? Why?

When a sound wave passes through tissue, there is some energy loss due to frictional effects. The absorption of energy in the tissue causes a reduction in the amplitude of the sound wave. The amplitude A at a depth x cm in a medium is related to the initial amplitude Ao (x = 0) by the exponential equation A = A₂e-ax. Where a, in cm³¹, is the absorption coefficient for the medium at a particular frequency. The table below gives some typical absorption coefficients. The intensity is proportional to the square of the amplitude, and its dependence on depth is I = = loe-2ax 1
Transcribed Image Text:When a sound wave passes through tissue, there is some energy loss due to frictional effects. The absorption of energy in the tissue causes a reduction in the amplitude of the sound wave. The amplitude A at a depth x cm in a medium is related to the initial amplitude Ao (x = 0) by the exponential equation A = A₂e-ax. Where a, in cm³¹, is the absorption coefficient for the medium at a particular frequency. The table below gives some typical absorption coefficients. The intensity is proportional to the square of the amplitude, and its dependence on depth is I = = loe-2ax 1
Where I is the incident intensity at x = 0 and I is the intensity at a depth x in the absorber. Material Frequency (MHz) Muscle 1 Fat 0,8 Brain (on average) 1 Bone (human skull) 0,6 0,8 a (cm-¹) 0,13 0,05 0,11 0,4 0,9 1,7 3,2 4,2 5,3 7,8 2,5 x 10-4 Half - Value Thickness (cm) 2,7 6,9 3,2 0,95 0,34 1,2 0,21 1,6 0,11 1,8 0,08 2,25 0,06 3,5 0,045 Water 1 1,4 × 10³ Table 1: Absorption Coefficients and Half-Value Thickness for various Substances The half-value thickness (HVT) is the tissue thickness needed to decrease lo tolo. Table 1 gives the typical HVTs for different tissues. Note the high adsorption in the human skull and that the absorption increases as the frequency of the sound increase. This increasing absorption with frequency also occurs for other body tissues and limits the maximum frequencies that can be used clinically.
Transcribed Image Text:Where I is the incident intensity at x = 0 and I is the intensity at a depth x in the absorber. Material Frequency (MHz) Muscle 1 Fat 0,8 Brain (on average) 1 Bone (human skull) 0,6 0,8 a (cm-¹) 0,13 0,05 0,11 0,4 0,9 1,7 3,2 4,2 5,3 7,8 2,5 x 10-4 Half - Value Thickness (cm) 2,7 6,9 3,2 0,95 0,34 1,2 0,21 1,6 0,11 1,8 0,08 2,25 0,06 3,5 0,045 Water 1 1,4 × 10³ Table 1: Absorption Coefficients and Half-Value Thickness for various Substances The half-value thickness (HVT) is the tissue thickness needed to decrease lo tolo. Table 1 gives the typical HVTs for different tissues. Note the high adsorption in the human skull and that the absorption increases as the frequency of the sound increase. This increasing absorption with frequency also occurs for other body tissues and limits the maximum frequencies that can be used clinically.
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