Relationship between tube current q and photographic distance r

The relationship between tube current q and photographic distance r is Q2=r22*Q 1/r 12.

The tube voltage is the most important factor. Tube voltage, tube current, noise time and focal plane are factors that often change according to lesions, which are usually called X-ray photography conditions.

If some photosensitive factors that affect the photosensitive effect change, other factors should be adjusted accordingly to ensure that the required photosensitive effect is basically unchanged.

Photosensitive effect: After X-rays pass through the examined part of human body, the photosensitive system (screen system, detector and other photoelectric conversion systems) can sense effective X-rays, thus producing the image effect needed for diagnosis.

Photosensitive factors: all factors related to photosensitive effect.

The main photographic conditions of x-rays:

1, tube voltage

Reflect the mass (penetration) and photon energy of X-rays.

2. Tube current

Reflects the number of x-rays. The greater the tube current, the greater the sensitivity, the smaller the quantum dot and the greater the X-ray dose.

3、AEC

At present, most DRs have AEC (Automatic Exposure Control) device, and the detector will automatically change the exposure parameters (tube voltage is fixed and tube current changes) according to the detection of X-ray dose value during pre-exposure to obtain relatively stable image quality.

Step 4 check

Main purpose: to reduce scattered rays reaching the detector. Use when the body thickness is ≥ 15cm or the tube voltage is ≥60. Most of them can be moved (lead shadow can be eliminated)

Three parameters: the gate ratio-generally110 of the tube voltage; Grating focal length-the distance from the grating plane to the focal point, which can give the adjustment range of SID; Grid density —— the number of lead bars in the range of1cm.

5. Irradiation field

The larger the irradiation field, the thicker the body thickness and the more scattering lines. It is best to reduce the irradiation field to the minimum including the irradiated part (special patients need flexibility); Generally, the irradiation field is smaller than the size of the detector, so that its periphery does not accept X-rays, and the photo quality is improved.