The reason for adopting tangent photography is

The reason for using tangent photography is to avoid image overlapping.

In order to clearly show some lesions with protruding and sunken edges, the central X-ray can pass through the local edge of the limb to prevent the lesions from overlapping with other parts. This method of photography is called tangent photography. The X-ray of tangent photography is a special position tangent to the projection site or organ. The common tangent position of skull, cheekbone and scapula is rarely used now.

Tangent photography is a special position where the center line of X-ray is tangent to the edge of the photographed part. X-ray plain film examination is one of the most commonly used image examination methods. If the photos are good, most patients can make a definite diagnosis. However, plain film is often affected by exposure conditions, lesion site and whether the patient is well prepared before examination, so it is difficult to fully display the lesion, resulting in missed diagnosis and misdiagnosis.

Image tangent point positioning method

1, tangent method

Tangent method refers to the method of manually rotating the reticle on the screen or in the lens, aiming at the two edges of the workpiece respectively, and measuring the angle through encoder or circular grating counting. This method can be divided into two types: projection tangent method, such as projector, tool measuring microscope and so on. Image tangent method, such as imager and video microscope with video function, relies on oblique tangent rotation measurement provided by software. Tangent method is convenient and simple to operate, but it is low in intensive reading, which is suitable for rapid batch inspection.

2, integral calculation method

The point calculation method is more appropriate. All geometric elements have some components, including the basic elements of lines, curves and arcs. Two-dimensional plane angle consists of two straight lines of basic geometric elements and countless points. Therefore, whether the angle measurement is accurate is the most critical.

Baidu Encyclopedia-Tangent Position