Imaging of the body is often complicated by the fact that anatomic structures overlap each other. Diagnostic accuracy of radiographs generally refers to how well an exam can predict the presence (or absence) of a disease or condition. The technologist plays a pivotal role in improving diagnostic accuracy by providing diagnostic images. This requires a technologist to be aware of the various positions and techniques required to isolate and provide a clearer view of a body part being imaged. In addition to better viewing an anatomic part, different projections also help anatomize an abnormality or localize a foreign body.
Issues of Concern
Understanding patient positioning requires a knowledge of the basic terminology relating to radiographic positioning:
- Anterior denotes the front of a body part, while the posterior denotes the back.
- Superior denotes the top of a body part, while inferior denotes the bottom.
- Medial indicates towards the midline.
- Lateral indicates a location away from the midline.
- Proximal is towards the body’s center.
- Distal denotes being away from the body’s center.
- Cranial indicates towards the head and caudal towards the feet.
- The axial plane indicates the horizontal plane with relation to the body’s long axis. This is true through the ankle. However, the axial and coronal planes in the mid- and forefoot are flip-flopped. To limit confusion when describing anatomic planes of the foot, it is better to use the terms short axis, long axis, and sagittal.
- The sagittal plane indicates the vertical plane that is parallel to the midsaggital plane.
- The coronal plane is the vertical plane that is perpendicular to the median plane.
- Prone denotes lying face-down, while supine denotes lying on one’s back.
- The anatomic position is with the hands supinated (palms forward). This places the thumbs lateral. However, to limit confusion when addressing a location in the upper extremities, it is more common to use the terms radial and ulnar instead of medial and lateral.
Movement: Describing the movement of joints with respect to standard positions helps us communicate and describe a patient orientation. Flexion corresponds to a decrease in the joint angle, while extension describes an increase in the joint angle. Abduction refers to the movement of a limb away from the midline, while adduction corresponds to the movement of the limb towards the midline. Pronation corresponds to the movement of the hand and forearm that brings the palm and hand facing posteriorly. Supination corresponds to the movement of the hand or forearm to bring the palm facing anteriorly. Eversion used in the context of the foot describes the movement of the sole away from the median plane, while inversion refers to the movement of the sole towards the median plane.
Projections: X-rays travel in a straight line with beams diverging from a source. The initial structures hit by a beam will be magnified in relation to those closest to the detector. Therefore structures that need to be measured with better accuracy need to be placed closer to the detector. The central ray is a simplified way of indicating the direction in which an x-ray beam travels. Different projections describe how the central ray travels through anatomy. Anterior-posterior denotes that the central ray passes first through the anterior anatomy and exits posteriorly, while the posterior-anterior denotes that the central beam passes from posterior to anterior. These terms also give an indication of which structures are closer to the detector. In anterior to posterior (AP) radiographs, the posterior structures are closer to the detector, and in posterior to anterior (PA) images, the anterior structures are closer to the detector. Therefore, as an example, chest radiographs are generally obtained PA to minimize magnification of the cardiac silhouette. This isn't possible for portable chest radiographs, which are by necessity obtained as AP resulting in a magnification of the cardiac structures. Lateral indicates a trajectory of the central ray passing from one side of the body to the other. An oblique projection corresponds to a central ray trajectory through a plane angled to the transverse plane or coronal plane. An axial projection corresponds to a central ray that passes through the long axis of the body.
Positioning: Several dozen standard radiographic exams with the chest radiographs and evaluation of the shoulder and knee joints are considered the most commonly requested studies. Some of the commonly ordered radiographic exams and highlighted instructions with respect to patient positioning are described below.
Chest: Patients are positioned for chest radiographs with an erect posture of the chest and a slightly extended chin. The hands are placed on the hips with the palms facing out, and the shoulders are rolled forward. The central ray is centered on the center of the lung fields, and it is important to ensure that there is no rotation of the thorax on frontal radiograph acquisition. As mentioned above, chest radiographs are obtained in the PA position with the front of the chest against the detector to minimize the magnification of the cardiac silhouette. The lateral chest radiograph requires the left side to be positioned against the image receptor, thereby minimizing cardiac magnification. The arms are raised and crossed above the head. The chin extended, and the thorax is without rotation or tilt. The thorax is centered on the central ray and to the image receptor anteriorly and posteriorly. For a lateral decubitus chest radiograph, the patient lays on the side (either right or left) with the arms above the head and the chin up. The central ray is centered at the level of the T7 vertebra. Positioning for oblique radiographs requires rotation at approximately 45 degrees.
Upper Airways: For upper airway radiographs evaluating the trachea and the larynx, the patient stands erect in a seated or standing position. The chin is raised slightly with the arms down and the shoulders depressed. For the AP position, it is important to ensure that there is no rotation and that the sternoclavicular joints have a symmetric appearance. On the lateral view, the field of view can be adjusted based on the area of interest.
Hand: When acquiring hand radiographs, the patient is typically seated at the end of the table with the elbow in flexion. The technologist should align the long axis of the hand, generally parallel to the image receptor. The hand should be in pronation with the digits slightly separated. For an oblique view of the hand, there should be a rotation of the hand of approximately 45 degrees. This is ideally performed with a support apparatus to have the hand rested on, with the digits slightly separated. The lateral hand radiograph requires the digits to be separated and spread into a fan-like position and ideally supported with a step block that is radiolucent. The Norgaard or "Ball-catchers" view requires the medial (ulnar) aspect of the hands to be closely approximated with the palms up and the hands obliqued 45 degrees. This view is commonly employed when evaluating for rheumatoid arthritis.
Wrist: The patient is positioned in the seated position with the arm on the table. The wrist is parallel to the surface of the image receptor without rotation. The hand is pronated with the fingers flexed. The wrist should be in direct contact with the surface of the image receptor. On lateral view image acquisition of the wrist, the humerus, forearm (and the wrist) should be maintained on the same horizontal plane. The wrist is parallel to the surface of the image receptor and is positioned in a true lateral position. The oblique view is obtained with the wrist rotated 45 degrees so that the ulnar aspect of the wrist is resting on the image receptor while the radial side is elevated. If the ordering clinician is concerned about a scaphoid fracture, an ulnar deviation (scaphoid) view of the wrist may be requested. This is basically the same as a standard PA view with the hand/wrist resting flat on the image receptor, but instead of a neutral (straight) position of the hand/wrist, the hand/wrist is deviated to the ulnar side, thereby elongating the scaphoid. If there is a concern for injury to the scapholunate ligament, the provider may order a clenched fist view used to evaluate for a widening of the scapholunate interval. Widening of the scapholunate interval suggests ligament injury. The clenched fist view is similar to the PA view of the wrist, but the fingers are tightly flexed instead of loosely flexed.
Forearm: For an AP view of the forearm, the patient is seated at the end of the table. The arm is extended, and the hand is supinated (palm up). The wrist and elbow joints are included within the field of view. To acquire a lateral forearm radiograph, the elbow should be flexed in 90 degrees during the acquisition of a true lateral position. This is obtained by resting the flexed elbow and forearm on the receptor with the ulnar side down (on receptor) and the radial (thumb) side up (closer to the beam).
Elbow: The AP elbow radiograph requires the elbow to be extended with the hand supinated. An AP oblique radiograph requires the elbow to be oriented 45 degrees in internal rotation. A lateral radiograph of the elbow requires the elbow to be flexed 90 degrees with the forearm and humerus laying flat on the table and the image receptor, ulnar side down on the receptor, and thumb/radial side up.
Humerus: The humerus AP radiograph is obtained with the patient standing erect or supine with the humerus aligned to the long axis of the image receptor. The arm needs to be abducted slightly with the supination of the hand for a true AP View. A lateral radiograph of the humerus can be obtained in different ways. For example, one method of obtaining a lateral view includes placing the image receptor vertically between the arm and the thorax.
Shoulder: A shoulder series typically includes at least two orthogonal views (for example, anterior-posterior and the lateral or scapular Y view) of the glenohumeral joint. For the AP view, the arm is slightly abducted, and the thorax can be rotated to place the posterior shoulder against the image receptor. The center of the image receptor is at the glenohumeral joint. The arm/hand can be in a neutral, internal, or external position affecting the projection of the humeral head. Multiple additional modifications can be obtained depending on the clinical scenario and department protocols. Additional projections include axillary and Grashey views (AP oblique). The Grashey view is obtained with the patient rotated 35-45 degrees, so the x-ray beam is parallel to the articular surface of the glenoid. The axillary view is a substitution for the scapular Y view. In the setting of trauma, it is a more reliable assessment of glenohumeral alignment as it is less susceptible to errors related to patient positioning and technique. An understanding of the expected normal radiographic appearance is essential for image interpretation. For example, in the setting of posterior shoulder dislocation, AP views of the shoulder obtained with internal and external rotation may look similar due to entrapment of the dislocated humeral head on the glenoid. Under such circumstances, the technician must label the images as internal and external rotation to clue to the radiologist that these represent two unique images and not a repeat of one view. Another clue to the presence of posterior glenohumeral dislocation is an overlap of the humeral head and glenoid on the Grashey view or lack of overlap on the AP view.
Foot: For the anterior-posterior image acquisition of the foot, the patient is in a supine or seated position with the plantar surface on the image receptor. The foot is extended with the plantar surface placed flat on the image receptor. The anterior-posterior medial oblique view requires the foot to be obliquely positioned 30 to 40 degrees. Lateral radiograph requires the patient to be recumbent on the affected side with the knee flexed. The plantar surface of the foot is perpendicular to the image receptor, thereby acquiring a true lateral image. The weight-bearing anterior-posterior foot radiograph requires the patient’s weight to be evenly distributed with both feet on one image receptor. The weight-bearing lateral image requires the image receptor to be placed vertically between the feet and high enough for a horizontal central ray.
Ankle: The patient is supine or seated on the table with the leg extended. The ankle and leg are aligned parallel to the edge of the image receptor. There should be no rotation to acquire a true anterior-posterior view. For the ankle mortise view, the long axis of the foot is internally rotated 15 to 20 degrees to have the intermalleolar line parallel to the tabletop. For the lateral ankle view, the patient is in a lateral recumbent position on the table with the foot dorsiflexed 90 degrees. The lateral aspect of the ankle is generally placed against the receptor with an X-ray beam directed from medial to lateral.
Tibia-fibula: For the AP view of the tibia-fibula, the leg is extended while ensuring no rotation of the knee or ankle. For the lateral view, the unaffected limb is placed behind the patient with the affected side down. Support can be placed along the distal aspect of the affected foot to obtain a true lateral image.
Knee: For the AP view of the knee, the leg is extended and centered to the central ray. The leg is rotated slightly inward in order to place the knee and the lower leg in a true anterior-posterior position. The image receptor is centered on the central ray. For a lateral view, the patient is positioned on the affected side, with the knee flexed 20-30 degrees. One method to obtain the tunnel view is to have the knee flexed 40-50 degrees with the patient prone and support placed under the tibia-fibula.
Considering radiographs are the most important and frequently used modality in clinical imaging, standardized patient positioning techniques are essential in evaluating any pathology of the body part being imaged. Frontal and lateral views of the chest allow a radiologist to evaluated for heart size, location of pneumonia, the volume of pneumothorax, among other disease processes. The use of both frontal and lateral views assist in accurately localizing processes, including foreign bodies in the setting of aspiration or projectile injury. Inappropriate patient rotation can degrade these images and the ability to evaluate subtle findings. The role of standard radiographs is somewhat limited in abdominal imaging. Erect and supine abdominal radiographs can evaluate for free air, although erect radiographs are more sensitive in evaluating free air. Appropriate patient positioning can also affect the evaluation of small bowel obstruction, stool burden, portal venous gas, and abnormal calcifications. Appropriate positioning in mammography is even more critical in identifying the location of microcalcifications, a finding suspicious for malignancy. Correct localization of microcalcifications on mammography is essential for planning percutaneous biopsy and localization for definitive surgical treatment of breast cancer.
The importance of appropriate patient positioning is probably most important in the setting of musculoskeletal imaging. Multiple projections assist in characterizing fractures, joint alignment, and other pathologies such as arthritis and tumors. Non-standard projections can potentially lead to missed diagnoses and associated morbidity. The importance of standard flexion and extension positioning is paramount, considering these positions can affect the appearance of standard anatomy on radiographs. The potential for ascribing a diagnosis in the setting of a normal study (i.e., a "false positive") is important to consider when anatomy appears altered due to non-standard positioning and projections. The technologist, therefore, has a crucial role in the delivery of standard techniques in image acquisition.
Nursing, Allied Health, and Interprofessional Team Interventions
Interprofessional communication is critical between a technologist, the radiologist, and the ordering provider in the following scenarios:
- An ordering provider requests for non-standard projections and views
- Non-standard views were provided due to technical factors related to the patient (patient movement, non-compliance, or altered anatomy)
- Technical factors outside the control of the technologist, such as in the setting of trauma where expedited images are required to evaluate for life-threatening diagnoses (such as pneumothorax)
- Technical factors outside the control of the technologist relating to the x-ray machine (i.e., an apparatus/machine-related image degradation)
- A radiologist requires additional views to evaluate further a pathology that is limited in evaluation with standard views.
- Appropriate clinical history provided to the radiology department is essential to ensure the correct examination is performed with the appropriate views and aides the radiologist to focus examination to pertinent findings and assign the appropriate differential diagnosis to those findings. For example, providing the radiologist with chronicity and location of symptoms, any significant medical history such as recent trauma or surgical procedures, and the presence of any chronic illnesses to include malignancy will result in a more useful and accurate radiology report. This does not mean that the provided history needs to be a verbose summary of the patient's entire medical history. An example of an appropriate, complete radiology request could be something like "55-year-old male with a 6-week history of atraumatic shoulder pain and history of multiple myeloma" or "25-year-old male with acute penetrating injury to the ball of the foot with concern for a retained foreign body".
- Documented communication and understanding of critical results from the radiologist to the ordering provider in cases of life-threatening conditions is a vital part of the patient's imaging evaluation. Examples would include pulmonary embolism, acute stroke, or pneumothorax. Equally important is the communication of urgent results such as a new diagnosis of malignancy, ectopic pregnancy, ovarian or testicular torsion, which require referral to subspecialists for timely patient treatments.
The difficulty of communication between non-medical radiology staff and other healthcare team members is a known limitation in delivering healthcare, especially when relating to oral and written inter-professional communication. Feedback between technologists and clinicians (and radiologists) is essential when images are limited due to technical factors, and this subsequently limits the determination of a diagnosis or identifying pathology. Clear communication between healthcare team members is a known factor in medical errors, and improving communication is essential to being a high-reliability organization.