Chest X-Ray Techniques

Chest X-ray

• Importance of chest x-ray: It is the most common requested x-ray examination in the radiology department, as most diseases manifest in the chest, and the chest contains important organs like lungs, heart, and great vessels.
• Quality of chest x-ray: Quality chest x-rays are essential for diagnosis, and this can be achieved by strict adherence to protocols.

Respiration

• Chest x-ray on arrested deep inspiration: This helps in the distension of the lung field for maximum visualization.
• Assessing the adequacy of inspiration: The number of ribs above the diaphragm should be counted (9 or 10 posterior ribs, 6 or 7 anterior ribs).
• Breathing techniques: The radiographer should practice breathing techniques with the patient for at least three times before the exposure is made.
• Avoiding motion unsharpness: A few moments should be allowed to elapse to ensure stability before exposure.

Exposure Parameters

• Choice of exposure parameter: Depends on the operational protocol of the department, but the basic objective is to acquire an image of the chest that will demonstrate the whole structures without interference from the surrounding regions.
• Kilovoltage Peak (kVp):
  • Low-kVp technique: Selected when the exposure is made without the use of a grid.
  • High-kVp technique: Involves the use of a grid.
  • Selection of appropriate kVp: Should be in keeping with the patient's thickness, habitus, and pathology.
• Focus Film Distance (FFD):
  • To obtain a quality image with minimal magnification of the intra-thoracic structures, especially the heart and other structures at differing distances from the film.
  • FFDs in the range of 150-180 cm are selected.
  • The FFD must be kept constant for any department to allow comparison of successive films.

Time

• Exposure time: Should be kept as low as possible (in the millisecond range) to minimize involuntary movement of the heart and great vessels.
• Achieving short exposure times: Can be obtained with high-output units at the higher mA settings, balanced with the speed of the film and screen combination and the kilovoltage selected.

Identification

• Accurate identification of chest radiographs: Essential, with information such as right and left sides, patient's name, date, hospital number, and radiology identification number being distinguished clearly.

Patient Preparation

• Patient preparation: The patient should undress and put on an x-ray gown, and radiopaque materials within the area of interest should be removed.
• Long hair and dangling earrings: Should be well parked and removed, respectively.

Projections (Views) in Chest X-ray

• Erect or decubitus position: Chest x-ray is taken in an erect or decubitus position, with the erect position being preferred.
• Advantages of erect position: Simple to position the patient, control of respiration is easy, gravitational force helps to expose maximum area of the lungs, and air-fluid level can easily be identified.

Postero-Anterior (PA) Erect Projection

• Position of patient: The patient is positioned facing the cassette, with the chin extended and centered to the middle of the top of the cassette.
• Cassette size: A cassette size of 35 x 43-cm or 35 x 35-cm is used, depending on the size of the patient.
• Centering point and beam direction: The horizontal beam is centered at right angles to the cassette at the level of the eighth thoracic vertebrae.

Alternative Projections

• Antero-Posterior (AP) Erect: Used in patients with kyphosis and when it is unsafe for patients to stand or sit in the basic position.
• Antero-Posterior (AP) Supine: Used on unconscious, immobile patients, and in children.
• Antero-Posterior (AP) Semi-Erect: Used on immobile patients.

Supplementary Views

• Lateral Projection:
  • Done when interested in the localization of lesion and demonstration of anterior mediastinal masses not seen on the PA projection.
  • Patient position: The patient is turned to bring the side under investigation in contact with the cassette.
• Apical Projection:
  • Done when the lesions in the apical lobes of the lungs are obscured by either the clavicle or the ribs.
  • Can be taken either in PA view or in AP view.
• Lordotic Projection:
  • Used to demonstrate interlobar pleural effusion (laminar effusion) or right middle lobe collapse.
  • Patient position: The patient is in PA position, holding the sides of the vertical bucky, and bends backwards at the waist with the degree of dorsiflexion varying from patient to patient.

Quality of a Good Chest X-ray

• A good chest x-ray should:
  • Be well collimated to include the entire thoracic cage with the apices and costophrenic angles well demonstrated.
  • Demonstrate the soft tissue layer of the chest.
  • Show the trachea equidistant between both clavicular heads.
  • Not have the scapula obscure the lung field.
  • Demonstrate the lungs well inflated with about 9 posterior ribs seen above the dome of the diaphragm.
  • Have the anatomic marker well positioned.
  • Be well penetrated with the vertebrae just visible behind the heart.
  • Be devoid of artifacts.
  • Have clear identification without obscuring the area of interest.

Measurement of Heart Size

• Cardiothoracic ratio (CTR): Calculated on chest radiograph taken in postero-anterior position.

• CTR formula: CTR = (a + b)/c

• Normal value: ≤ 0.5### Patient Position and Cassette

• Patient lies in a supine position on the hospital stretcher with shoulders depressed by caudally applying traction to the arms if there is no injury to the arms.

• This enables demonstration of the C7/T1 junction, a common site of injury.

• The cassette is either supported vertically on the bed or placed in an erect cassette holder with the top of the cassette at the level of the ear.

Supplementary Projections

• Right and left posterior oblique views (erect and supine)
• Lateral flexion and extension
• Swimmer's view

Right and Left Posterior Oblique Projections (Erect)

• Recommended in cases of trauma and degenerative diseases.
• Main aim is to examine the intervertebral foramina and the relationship of the facet joints in cases of suspected dislocation or subluxation.
• Patient stands or sits with the posterior aspect of their head and shoulder against the vertical cassette holder.
• The mid-sagittal plane of the body is rotated through 45° for right and left sides.
• The head is rotated so that the mid-sagittal plane of the head is parallel to the cassette to avoid superimposition of the mandible on the vertebra.
• The cassette is centered at the prominence of the thyroid cartilage.
• Collimate to avoid irradiation of the eyes.

Beam Direction and Centering Point

• Horizontal beam is angled 15° cephalad, and the central ray is centered to the middle of the neck on the side nearest to the tube.
• The intervertebral foramina shown are the side nearer to the cassette.

Right and Left Posterior Oblique Projections (Supine)

• Done in cases of severe trauma where it is impossible for the basic views to demonstrate the lower cervical vertebrae.
• Patient lies supine on the casualty trolley, and the cassette is gently slotted under the patient's neck without moving the patient.
• The beam is angled 30-45° to the mid-sagittal plane, and the central ray is directed towards the middle of the neck on the side nearest to the tube at the level of the thyroid cartilage.

Lateral Swimmer's Projection

• Done when the lateral view cannot show all the vertebrae, especially the cervico-thoracic junction, which is a result of superimposition of the vertebrae by the shoulders.
• Patient lies on the casualty trolley, stands or sits with either side of the body against an erect cassette stand with the mid-sagittal plane parallel to the cassette.
• The arm nearer to the cassette is folded over the head with the humerus as close to the cassette stand top as possible.
• The shoulders are now separated vertically, and the cassette is adjusted so that the vertebrae will be at the middle of the cassette.

Beam Direction and Centering Point

• The horizontal beam is directed to the middle of the cassette at a level just above the shoulder far away from the cassette.

Lateral Flexion and Extension Projections

• Done in cases of trauma, degenerative bone disease, and in theatre to assess the degree of movement of the neck.
• Patient is positioned for the basic lateral view, and then asked to flex the neck and tuck in the chin as far as possible or extend the neck and raise the chin as far as possible.
• The patient is advised to hold onto something for immobilization.

Beam Direction and Centering Point

• The horizontal central ray is directed towards the middle of the neck.

Thoracic Vertebrae

• Located between the cervical and lumbar vertebrae.
• Stacked upon each other to form a kyphotic curve in the lateral view.
• Twelve in number, identified as T1-T12 vertebrae.
• The region has an extremely high contrast due to the superimposition of the air-filled trachea over the upper thoracic vertebrae.
• Strategies employed to overcome high radiographic contrast include:
  • Use of anode heel effect.
  • Use of graduated screen or wedge filters.
  • Use of high kVp (80kVp or more).

Basic Projections

• Anteroposterior (AP) and Lateral.

Anteroposterior (AP) Projection

• Patient lies supine on the x-ray couch with the mid-sagittal plane perpendicular to the center of the tabletop.
• Knee and hip are flexed so that the plantar aspect of the foot is in contact with the table.
• Foam pads are placed under the knee for stability and comfort.
• Arms are placed by the sides.
• Cassette should be long enough to include C7 and L1 vertebrae.
• Exposure is made on arrested inspiration.

Centering Point and Beam Direction

• Vertical central ray is directed at a right angle to the cassette and towards a point 2.5cm below the sternal angle.

Lateral Projection

• Patient lies on either side in lateral decubitus on the x-ray table.
• The mid-sagittal plane should be parallel to the cassette and the mid-axillary line coincides with the middle of the table.
• Arms are raised well above the head with the head supported with a pillow.
• Pads may be placed between the knees for comfort.
• The cassette should be long enough to include the lower cervical and upper lumbar vertebrae.

Centering Point and Beam Direction

• The central vertical ray should be at a right angle to the long axis of the thoracic vertebrae.
• Centered at a point which is 5cm anterior to the spinous process of T6/7.

Lumbar Vertebrae

• Five in number, identified as L1-L5.
• Form a lordotic curvature in the lateral view.
• Basic projections are Anteroposterior (AP) and Lateral.

Anteroposterior (AP) Projection

• Patient lies supine on the x-ray couch with the mid-sagittal plane coinciding with, and at a right angle to the midline of the table.
• The anterior superior iliac spine should be equidistant from the table top.
• Hip and knees are raised on a foam pad so that the plantar aspects of the foot are in contact with the table.
• Exposure is taken on arrested expiration.
• The cassette should be large enough to accommodate the lower thoracic vertebrae and the sacro-iliac joints.

Centering Point and Beam Direction

• Vertical central beam is directed towards the midline at the level of the lower costal margin, which corresponds to L3 vertebra.

Lateral Projection

• Patient lies on either side on the x-ray couch.
• The coronal plane which runs through the spine should coincide with the center of the table.
• Arms are raised and rested on the pillow in front of the patient's head.
• Knees and hips are flexed for stability.
• Exposure is made on arrested expiration.

Centering Point and Beam Direction

• Vertical central ray is directed at a right angle to the line of spinous processes and centered towards a point 7.5cm anterior to the third lumbar spinous process at the level of the lower costal margin.

Alternative Projections

• Lateral with horizontal beam (lateral shoot through) for suspected fracture of the lumbar vertebrae.

Lumbar-Sacral Junction

• Basic projections are Anteroposterior (AP) and Lateral.

Anteroposterior (AP) Projection

• Patient lies supine on the x-ray couch with the median sagittal plane corresponding with and perpendicular to the midline of the Bucky.
• The anterior superior iliac spines should be equidistant from the table top.
• Knees are flexed over a foam pad for comfort and to reduce the lumbar lordosis.
• The cassette is placed cranially so that its center coincides with the central ray.

Centering Point and Beam Direction

• Central ray is directed 10-20° cranially from the vertical and towards the midline at the level of the anterior superior iliac spines.

Lateral Projection

• Patient lies on either side on the x-ray couch with the arms raised or the hand resting on the pillow.
• The knees and hip are flexed slightly for stability.
• The dorsal aspect of the trunk should be at a right angle to the cassette.
• The cassette is centered at the level of the 5th lumbar vertebra.

Supplementary Projections

• Right or left posterior oblique views.

Patient Positioning

• Patient lies supine on the x-ray couch and then rotated to the right and left sides in turn.
• The median sagittal plane is at 45° to the table top.
• The hip and knees are flexed and the patient is supported with a 45° foam pad placed under the trunk on the raised side.
• The cassette is displaced cranially at the level to coincide with the central ray.

Learn about the importance and protocols for producing quality chest x-rays for disease diagnosis. This quiz covers the key aspects of chest x-ray examination in radiology.