Clark's Pocket Handbook for Radiographers (Clark's Companion Essential Guides)

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The same result can be achieved by raising the orbito-meatal baseline by 20 degrees with no caudal angulation applied to the tube (see image). The patient lies supine, with the head raised and immobilized on a non-opaque skull pad. This will ensure that the occipital region is included on the final image. The head is adjusted, such that the median sagittal plane is perpendicular to the table/trolley and the inter-orbital line is perpendicular to the image receptor. Support the image receptor with grid vertically against the lateral aspect of the head parallel to the median sagittal plane, with its long edge 5 cm above the vertex of the skull. The horizontal central ray is centred to the palpable coracoid process of the scapula. The primary beam is collimated to include the head, the greater and lesser tuberosities of the humerus, together with the lateral aspect of the scapula and the distal end of the clavicle.

Care should be taken when a supracondylar fracture of the humerus is suspected. In such cases, no attempt should be made to extend the elbow joint, and a modified technique must be employed. For CR, a 35 ⫻ 43-cm image receptor is used for adults, with the lower leg placed diagonally to ensure the full length of the tibia and fibula is included. The patient is either supine or seated on the X-ray table, with both legs extended. The ankle is supported in dorsi-flexion by a firm 90-degree pad placed against the plantar aspect of the foot. The limb is rotated medially until the medial and lateral malleoli are equidistant from the image receptor. The lower edge of the image receptor is positioned just below the plantar aspect of the heel.Problems can occur with producing an optimal image with this technique, due to a number of factors, including patient movement and positioning errors. It is essential that the patient is able to co-operate and stay still for up to 20 seconds for a successful examination to take place.

The patient lies on the side to be examined, with the knee flexed at 45 or 90 degrees. The other limb is brought forward in front of the one being examined and supported on a sandbag. A sandbag is placed under the ankle of the affected side to bring the long axis of the tibia parallel to the image receptor. The position of the limb is now adjusted to ensure that the femoral condyles are superimposed vertically. The centre of the image receptor is placed level with the medial tibial condyle. The image must demonstrate the third cervical vertebra down to the cervical-thoracic junction. Lateral collimation to soft tissue margins. The chin should be superimposed over the occipital bone. Always prepare the X-ray room for the procedure prior to the patient entering the room. Follow departmental protocols for the examination, e.g. the focus receptor distance (FRD), normally 110 cm unless otherwise stated. If using computed radiography: 1 do not take multiple projections on one receptor/plate as this will confuse image processing algorithms; 2 use the smallest receptor size consistent with size of the body part to maximize resolution. Always collimate to the area of interest as excessive field sizes reduce image quality and increase patient dose. It is best practice to apply anatomical side markers at the time of the examination and not to use electronic markers when post processing the image.

All the cranial bones should be included within the image, including the skin margins. It is important to ensure that the skull is not rotated. The petrous ridges should appear just below the inferior orbital margin. The image must include the upper third of the femur. When taken to show the positioning and integrity of an arthroplasty, the whole length of the prosthesis, including the cement, must be visualized. The horizontal central ray is directed to the anterior aspect of the patient and centred to the centre of the image receptor. The patient sits or stands facing the image X-ray tube. The patient’s position is adjusted so that the middle of the clavicle is in the centre of the image receptor.

The image should be of comparable quality to that described for the postero-anterior chest projection. The image should demonstrate superimposition of the femoral condyles and a clear view of the soft tissues proximally to the patella (supra-patellar pouch). CHEST – ANTERO-POSTERIOR (ERECT) This projection is often used as an alternative when the postero-anterior projection cannot be performed due to the patient’s condition. Frequently the patient is supported sitting erect on a chair. Give clear instructions Explain what you are doing Explain why you are doing it Invite and answer any questionsThe image should demonstrate clearly the joint space between the head of the humerus and the glenoid cavity. Outer canthus of the eye: the point where the upper and lower eyelids meet laterally. Infra-orbital margin/point: the inferior rim of the orbit, with the point being located at its lowest point. Nasion: the articulation between the nasal and frontal bones. Glabella: a bony prominence found on the frontal bone immediately superior to the nasion. Vertex: the highest point of the skull in the median sagittal plane. External occipital protuberance (inion): a bony prominence found on the occipital bone, usually coincident with the median sagittal plane. External auditory meatus: the opening within the ear that leads into the external auditory canal. Oblique Using Beam Angulation When the median sagittal plane is at right-angles to the receptor, right and left anterior or posterior oblique projections may be obtained by angling the central ray to the median sagittal plane. NB This cannot be done if using a grid unless the grid lines are parallel to the central ray. The central ray is angled cranially so it makes an angle of 30 degrees to the orbito-meatal plane. Adjust the collimation field, such that the whole of the occipital bone and the parietal bones up to the vertex are included within the field. Avoid including the eyes in the primary beam. Laterally, the skin margins should also be included within the field.