Question:
Hounsfield unit is a term, associated with which of the following imaging technique?
Hounsfield unit is a term, associated with which of the following imaging technique?
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To remember Hounsfield Units:
- Think of CT density.
- Remember the baseline: Water is 0, Air is -1000, and Bone is highly positive ($>$1000).
- Think of CT density.
- Remember the baseline: Water is 0, Air is -1000, and Bone is highly positive ($>$1000).
Updated On: Aug 3, 2026
- MRI
- CT scan
- Doppler ultrasonography
- Nuclear scintigraphy
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
The Hounsfield Unit (HU) is a quantitative scale used to describe radiodensity in computed tomography (CT) imaging.
Named after Sir Godfrey Hounsfield, who co-invented the CT scanner, this scale standardizes the grayscale values displayed on CT images.
Step 2: Detailed Explanation:
During a CT scan, X-ray beams pass through the body from multiple angles, and the detectors measure the attenuation of these beams.
The raw attenuation measurements are converted into Hounsfield Units using a linear transformation based on the physical density of the tissues.
The HU scale is anchored by two predefined reference points:
- Water is defined as exactly \(0 \text{ HU}\).
- Air is defined as exactly \(-1000 \text{ HU}\).
Other body tissues fall along this spectrum based on their physical density:
- Fat: \(-120 \text{ to } -90 \text{ HU}\)
- Soft tissue: \(+30 \text{ to } +60 \text{ HU}\)
- Bone: \(+1000 \text{ to } +3000 \text{ HU}\)
This scale is unique to X-ray based computed tomography (CT) and is not used in MRI (which uses signal intensity), ultrasound (which uses echogenicity), or scintigraphy (which uses gamma counts).
Step 3: Final Answer:
The Hounsfield unit is associated with the CT scan.
The Hounsfield Unit (HU) is a quantitative scale used to describe radiodensity in computed tomography (CT) imaging.
Named after Sir Godfrey Hounsfield, who co-invented the CT scanner, this scale standardizes the grayscale values displayed on CT images.
Step 2: Detailed Explanation:
During a CT scan, X-ray beams pass through the body from multiple angles, and the detectors measure the attenuation of these beams.
The raw attenuation measurements are converted into Hounsfield Units using a linear transformation based on the physical density of the tissues.
The HU scale is anchored by two predefined reference points:
- Water is defined as exactly \(0 \text{ HU}\).
- Air is defined as exactly \(-1000 \text{ HU}\).
Other body tissues fall along this spectrum based on their physical density:
- Fat: \(-120 \text{ to } -90 \text{ HU}\)
- Soft tissue: \(+30 \text{ to } +60 \text{ HU}\)
- Bone: \(+1000 \text{ to } +3000 \text{ HU}\)
This scale is unique to X-ray based computed tomography (CT) and is not used in MRI (which uses signal intensity), ultrasound (which uses echogenicity), or scintigraphy (which uses gamma counts).
Step 3: Final Answer:
The Hounsfield unit is associated with the CT scan.
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