Introduction
创建时间
Apr 10, 2024 08:22 AM
标签
X-rays
基础知识
high-speed electrons
shorter wavelength (about to )
The higher the atomic number, the denser the element and the more effectively the X- ray is blocked. 原子序数越高，元素的密度越高，X射线被阻挡的效果越好。
vary by atomic number (the number of protons in the nucleus).
bones → calcium → blocked → white
lungs → nitrogen (氮) → through → black
Fracture → black (骨头内，中间有空隙，所以骨折为黑色)
Five basic radiographic densities
- Metal (Bright white)
- Mineral (White)
- Fluid/soft tissue (Gray)
- Fat (Dark gray)
- Air (Black)
其实就是按照相对原子质量来的
关于辐射 Three key elements of radiation safety
时间，距离，吸收屏障
Time, Distance, Shielding
没有安全剂量
暴露在辐射中产生自由基（free radical），多一个电子的分子
birth defects, cancer and cataracts
诊断
Basic concept: Analysis of any structure or mass on a radiograph
- Size of the structure
- Shape or contour of a structure
- Position of the structure
- Density of the structure
X-rays can penetrate through subtle pathology and obscure an important finding. A malignant pulmonary nodule may be difficult or impossible to see if the film is overpenetrated.
An underpenetrated (underexposed) radiograph can make normal structures such as broncho vascular structures in the lungs look like pathology. An underpenetrated image is too light or white-looking.
X-rays can penetrate through subtle pathology and obscure an important finding.
x射线可以穿透细微的病理，掩盖重要的发现。
A malignant pulmonary nodule may be difficult or impossible tod see if the film is overpenetrated.
恶性肺结节可能很难或不可能看到，如果膜是过度渗透。
An underpenetrated (underexposed) radiograph can make normal structures such as bronchovascular structures in the lungs look like pathology.
未透透(未曝光)x线片可以使正常结构，如肺中的支气管血管结构看起来像病理。
An underpenetrated image is too light or white-looking.
未穿透的图像太亮或看起来太白。
Computed tomography
Common CT-assigned attenuation values:
• Air = -1,000 HU or less (black)
• Fat = -5 to -50 HU (dark grey)
• Water = 0 HU (grey)
• Soft tissue = +40 to +80 HU (light grey)
• Calcium (stone) = +100 to +400 HU (grey white)
• Cortical bone = +1,000 HU (white)
-1000空气，0水，1000钙
Limitations
CT is worse in distinguishing soft tissue structures than MRI can.
Metal can create a “starburst artefact (星爆伪影)” that blurs the image.
CT is less sensitive than MRI in the detection of white matter disease of the brain.
MRI
With T1, water has no signal and is black.
With T2, water has high signal and is white.
open and closed magnets
open: slower, more comfortable
close: faster, more limited
T1 is often referred to as the anatomy sequence.
水或者水肿不明显，但是解剖结构明显
T2 is known as the pathologic sequence.
水肿时高信号（白色），容易被发现
Safety considerations: Mental, especially pacemaker.
Ultrasound
As the ultrasound energy travels through tissues of the body, it is scattered, transmitted, or reflected back to the transducer.
Ultrasound that is scattered does not help to create an image. Ultrasound that is transmitted produces an echo- free area on the image.
Reflected ultrasound creates a density on the ultrasound image.
1，液体之后的组织会更高亮（因为在液体中没有反射），所以可以看出囊肿
2，结石类完全反射，会产生一个黑洞
It works best on thin patients and on body parts closest to the skin.
