This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Ultrasonography, CT, and MRI, Subject name: Radiology
[{'content': 'Maximal valve of HU Unit - \nSelect and explain. \nA. Water, B. Fat, C. Soft tissue, D. Bone', 'role': 'user'}, {'content': "Answer: D \nExplanation: Ans. is 'd' i.e., Bone Hounsfield's number (CT number)o Hounsfield's contribution is memorialized in the Hounsfield scale, which is used to measure the x-ray attenuation in CT scanning. Water is arbitrarily assigned a value of 0 Hounsfield units (HU).o The basic parameter in a CT image is CT number. The CT number is defined with respect to water X-ray- absorption and is dependent on absorption / attenuation coefficiento When an X-ray beam (used in CT) passes through the body, there is a logarithmic attenuation of its intensity- over distance. A measurement of the intensity of the exiting beam is known as the linear attenuation coefficient when the attenuation thickness is 1 cm. The linear attenuation coefficient is related to the absorption in the material. This depends upon the energy of the X-ray beam and the type of material being irradiated. CT images are map of the relative linear attenuation coefficient of tissues. The relative attenuation coefficient is normally expressed in Hounsfield units (HU) or CT number.CT number / Hounsfield unit of a matter =ux-uH2O PHpx 100ux = Attenuation coefficient of matter.uH2O = Attenuation coefficient of water.SubstanceHL unitsWater0Dense cortical bone+ 1000 (+400 to - 1000)Soft tissue+ 40 to + 80Fat- 60 to -100Lung tissue- 400 to -600Air- 1000", 'role': 'assistant'}]