CRITERIA FOR GOOD THORAX X-RAY PERFORMANCE

Chest X-ray is one of the most frequently requested imaging studies in clinical practice, and its correct performance is essential for accurate diagnostic interpretation. The technical quality criteria that must be met for an adequate chest X-ray are detailed below:

1. Adequate projection

• Posteroanterior (PA) projection: This is the standard projection for outpatients. The patient is positioned upright, with the chest resting on the film and the arms positioned to avoid overlapping.

• Anteroposterior (AP) projection: Used in patients who cannot stand, usually in intensive care units. Although this projection tends to produce greater magnification of the heart, it is useful when the patient is bedridden.

• Lateral Projection: This view should be performed with the patient standing, positioning the left side of the chest against the image detector, with the arms elevated. This view is essential for evaluating lesions that may overlap the PA or AP projection.

  
  

2. Patient positioning

• The patient should be erect (if this is not possible, the lateral decubitus or supine projection is used) with the arms extended forward or above the head in the lateral projection, to avoid overlapping of the shoulder blades with the lung fields.

• The midsagittal line of the body should be aligned perpendicular to the image detector to avoid rotation . The clavicles should be symmetrical and equidistant from the spinous processes of the thoracic vertebrae.

• The projection should include the lung apices to the costophrenic angles, completely encompassing the lung parenchyma.

  
  

3. Breathing technique

• The patient should inhale fully to allow the lungs to fully expand, allowing visualization of at least 10 posterior ribs . Poor inhalation can mimic conditions such as consolidation or atelectasis.

• In cases where pleural pathology or pneumothorax is suspected, a second expiratory image is useful to improve visualization of abnormalities.

  
  

4. Technical exhibition criteria

• The radiograph should have sufficient penetration to allow visualization of the mediastinal structures and thoracic vertebrae through the heart.

• Exposure factors (kilovoltage and milliamperage) must be adjusted appropriately. Generally, a kilovoltage between 100 and 125 kVp is used for PA radiography, which allows for good penetration without generating noise.

• The use of an anti-scatter grid is essential in patients with a high body mass index, as it improves contrast by reducing scattered radiation.

  
  

5. Evaluation of artifacts

• It is crucial to avoid superimposition artifacts, such as jewelry, clothing buttons, probes, or cables that could interfere with the image. Cardiac monitoring electrodes must be temporarily moved during acquisition.

• In the hospital setting, invasive medical devices such as catheters, endotracheal tubes, and central lines are frequently present. Their correct positioning should be assessed and documented in the report.

  
  

6. Rotation indicators

• To assess whether the radiograph is correctly centered and without rotation, the spinous processes should be aligned equidistantly between the medial ends of the clavicles.

• Rotation can cause distortion in the size of cardiothoracic structures and alter the distribution of air in the lung fields, which can lead to incorrect interpretations.

  
  

7. Degree of magnification

• The PA projection minimizes magnification of cardiac structures. The AP projection, in contrast, magnifies the heart due to the greater distance between the detector and the X-ray source. It is important to take this effect into account when interpreting the image.

  
  

8. Collimation and centering

• Collimation should fully include the lung fields and mediastinum, with special attention to the costophrenic angles. Centration should be aligned with the fourth intercostal space in the midline to ensure complete visualization of the mediastinum and diaphragm.

  
  

9. Evaluation of the final image

• In a well-executed image, the posterior ribs should be visible above the diaphragm and the bony structures (ribs, clavicles, vertebrae) should be well delineated, without overexposure.

• Vascular structures and pulmonary shadows should be clearly distinguishable, without loss of contrast or excessive radiopacity. The diaphragm should be clearly visualized without elevations or irregularities.

• The cardiac silhouette should be defined, with proportions that allow assessment of the cardiothoracic ratio. A disproportionately large heart could indicate a technical problem (as in AP projections) or a pathological condition.

  
  

Conclusion

A well-performed chest radiograph is essential for an accurate diagnostic interpretation. Proper patient positioning, technical image quality, adequate exposure, and minimization of artifacts are essential to ensure reliable radiographic findings. Failure to meet these criteria can lead to diagnostic errors and the need for repeat studies, unnecessarily increasing the patient's exposure to ionizing radiation.