口腔放射学课件：根尖片投照技术比较

1、根尖片投照技术比较分线角投照技术Bisecting-angle projection principle平行投照技术Paralleling projection principle根尖投照技术123图像清晰度和分辨率Image sharpness and resolution尺寸失真Image size distortion形态失真Image shape distortion影响成像质量的因素是什么？清晰度密度差异Sharpness measures how well a boundary between two areas of differing radiodensity is revea

2、led. 分辨率精细度Image spatial resolution measures how well a radiograph is able to reveal small objects that are close together.010203根据实际情况，尽可能减小聚焦点Use as small an effective focal spot as practical.选择长、底端开放的线管，增加聚焦点到物体的距离Increase the distance between the focal spot and the object by using a long, open-e

3、nded cylinder.减小物体到胶片的距离Minimize the distance between the object and the film.如何提高？尺寸失真The divergent paths of photons in an x-ray beam cause enlargement of the image on a radiograph. Increasing the focal spot-to-film distance and decreasing the object-to-film distance minimizes image magnification.形

4、状失真1.Position the film parallel to the long axis of the object. 2.Orient the central ray perpendicular to the object and film. Ideal positioning requirements分角线投照技术的优点与缺点分角线技术的优点相对舒适Positioning of the film packet is reasonably comfortable for the patient in all areas of the mouth.定位简单Positioning is

5、relatively simple and quick.规范操作条件下，可满足诊断要求If all angulations are assessed correctly, the image of the tooth will be the same length as the tooth itself and should be adequate(but not ideal) for most diagnostic purposes.分角线技术的缺点图像失真的影响因素多The many variables involved in the technique often result in t

6、he image being badly distorted.每次校准。校准失误造成形状失真，图像重叠。技术要求高The horizontal and vertical angles have to be assessed for every patient and considerable skillis required. Incorrect vertical angulation will result in foreshortening or elongation of the image or over lapping of the crowns and roots.牙周骨组织显示不

7、清The periodontal bone levels are poorly shown.颧弓影与上磨牙牙根重叠The shadow of the zygomatic buttress frequently over lies the roots of the upper molars.可重复性低It is not possible to obtain reproducible views.胶片可能部分未被照射到Coning off or cone cutting may result if the central ray is not aimed at the centre of the

8、film,particularly if using rectangular collimation.不利于早期龋的发现The crowns of the teeth are often distorted, thus preventing the detection of approximal caries.颊根失真，缩短The buccal roots of the maxillary premolars and molars are foreshortened.平行投照技术的优点与缺点平行投照技术的优点不改变几何形状，伴有轻微放大效应Geometrically accurate imag

9、es are produced with little magnification.颧弓显示在磨牙根尖上The shadow of the zygomatic buttress appears above the apices of the molar teeth.牙周围骨组织、根尖周组织显示清晰The periodontal bone levels are well represented. The periapical tissues are accurately shown with minimal foreshortening or elongation.牙冠显示清晰，利于早期龋的发现

10、The crowns of the teeth are well shown enabling the detection of approximal caries.如果定位装置正确摆放，X线线管的水平和垂直向调节自动设定The horizontal and vertical angulations of the X-ray tube head are automatically determined by the positioning devices if placed correctly.X线束准确打在胶片中央，胶片所有范围被照射The X-ray beam is aimed accur

11、ately at the centreof the film-all areas of the film are irradiated and there is no coning off or cone cutting.可重复性Reproducible radiographs are possible at different visits and with different operators.不受患者头位的影响The relative positions of the film packet,teeth and X-ray beam are always maintained,irre

12、spective of the position of the patients head.This is useful for some patients with disabilities.平行投照技术的缺点 不适感，胶片放于后牙区可能引起咽反射Positioning of the film packet can be very uncomfortable for the patient, particularly for posterior teeth,often causing gagging.对操着者要求高Positioning the holders within the mout

13、h can be difficult for inexperienced operators.某些异常解剖造成平行投照技术难以实现The anatomy of the mouth sometimes makes the technique impossible, e.g.a shallow, flat palate.某些时候牙根靠近胶片（多根牙）The apices of the teeth can sometimes appear very near the edge of the film.下颌第三磨牙区操作困难Positioning the holders in the lower third molar regions can be very difficult.放大效应The technique cannot be performed satisfactorily using a short focal spot to skin distance (i.e.a short spacer cone) because of the resul