Liver Scanning And Liver Function In Cystic Fibrosis

Discuss about the Liver Scanning and Liver Function in Cystic Fibrosis.

 

 

While scanning a liver, I would choose to do it either between or under the ribs instead of through the ribs because when an ultrasound beam goes through the liver tissue and encounters a rib, it will reflect off. This is as a result of the difference in acoustic impedance of the liver tissue and the bone tissue in the ribs. Consequently, the imaging will be poor because a lot of sounds was reflected back leaving much lesser sound to penetrate through and complete the imaging. Acoustic impedance (Z) refers to the physical property of a tissue which explains the resistance that an ultrasound beam encounters when it goes through a tissue (Feigelson, Pecau and Perez 2014). Therefore, the ideal way to scan the liver is under the rib and not through the ribs in order to improve the quality of the imaging.

In this case, the quality of imaging will depend on the density of a tissue (p, in kg/m³) and the speed of the sound wave (c, in m/s) and is expressed as Z = p x c. In this case, an increase in the density of a tissue and the speed of sound will lead to a simultaneous increase in impedance (Bolondi and Piscaglia 2015). The amount of reflection that takes place when an ultrasound beam encounters a rib in a perpendicular direction is shown as Reflection fraction = [(Z₂ - Z₁) / (Z₂ + Z₁)] ² whereby Z₁ and Z₂is the impedance in the liver tissue and the rib tissue respectively. The impedance of the liver tissue is 1.65 × 10⁶ while that of the bone tissue is 7.8 × 10⁶.The reflection coefficients are expressed as:

The intensity of the ultrasound waves directed towards the liver can be compared with the ultrasound waves reflected back to the surface by the ribs. These reflected waves are usually lower in terms of intensity due to the reflection and as a result, a dB loss occurs (Harvey and Albrecht, 2012). The decibel value for the two different ultrasound waves may be calculated using the decibel scale used in acoustics where the decibel loss will be defined by:

l₀ is the reference intensity for the ultrasound. If the ultrasound wave intensity is halved, 3 dB values are subtracted and if the intensity is reduced by a factor of 10, 10 dB values are subtracted. The dB loss is usually denoted by a negative value because less than 1% of sound would be reflected where there is such an interface (Gollin, Sims and Cameron 2014).

In conclusion, the main reason why I will choose to scan the liver under the ribs and no through the ribs is because of the differences in the acoustic impedance of the liver and the bone tissues in the ribs which will substantially affect the quality of the image. Therefore, by scanning under the rib, the ultrasound beam will not undergo any resistance as it goes through the rib tissues.

Reference list

Bolondi, L., Correa, J.M., Lencioni, R., Wescott, H.P., and Piscaglia, F., 2015. New perspectives for the use of contrast-enhanced liver ultrasound in clinical practice. Digestive and liver disease, 39(2), pp.187-195.

Feigelson, J., Pau, Y. and Perez, R., 2013. Liver scanning and liver function in cystic fibrosis. Acta Paediatrica, 61(3), pp.337-342.

Gollin, F.F., Sims, J.L. and Cameron, J.R., 2014. Liver scanning and liver function tests: A comparative study. Jama, 187(2), pp.111-116.

Harvey, C.J. and Albrecht, T., 2012. Ultrasound of focal liver lesions. European radiology, 11(9), pp.1578-1593.