How to differentiate between low- and high-quality chest x-rays

Discover the five key identifying factors which will help you to distinguish between low- and high-quality chest x-rays.

Julian Dobranowski, MD FRCPC FCAR
Julian Dobranowski, MD FRCPC FCAR
17th Jan 2020 • 6m read

The quality of an x-ray image can often mean the difference between detecting a life-threatening pathology and missing it completely. In this lesson, you'll discover the five key identifying factors that will help you to distinguish between low- and high-quality chest x-rays.

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Video Transcript

[00:00:00] What will I gain from this video? After watching this video, you will be able to differentiate between good and bad quality examination. A good quality chest x-ray examination is one that allows the interpreter to extract the maximum clinical information, imported from it. False positive and false negative interpretations can increase significantly with poor quality x-ray images. The quality of the chest x-ray image relates to

[00:00:30] positioning, degree of inspiration, technical exposure factors, sharpness, and artifacts. On a good quality chest x-ray examination, the entire thorax should be visible and should be positioned in the center of the image. The image should include the apices of the lungs, the costophrenic angles, the spine, and the sternum. The medial edge of the scapula should lie lateral to the chest wall. The patient's arms

[00:01:00] and chin should not overlap the upper lung fields. On a good quality chest x-ray, there should be no patient rotation. If the patient is rotated, the lung closest to the x-ray detector may look whiter and the anatomy can look distorted. We take the following steps to assess for proper positioning on the PA x-ray. First, identify the lung apices, the costophrenic angles or the lower aspect of the

[00:01:30] lateral parts of the lungs, and the lateral margin of the lungs, all the way from the bottom to the top. Here, we can see the lungs extending all the way to the ribs. The lungs form an edge with the chest wall, laterally. Next, we identify the medial and both clavicles. The clavicles are easy to identify and I've highlighted them with this illustration.

[00:02:00] We identify the medial aspect of both clavicles. The spinous processes will look like oval densities, within the midline of the body. The patient will be well-positioned, if the distance between the spinous processes and the medial aspect of the clavicles, is equal on both sides. To assess for proper positioning on the lateral x-ray, we take several steps. One, we make sure that

[00:02:30] the superior aspect of the lungs is identifiable, and that the costovertebral angles were visible inferiorly. We make sure that the anterior aspect of the lungs extend to the chest wall anteriorly and to the ribs posteriorly. We make sure that the shadows of the arms and shoulders should not be superimposed on the lungs.

[00:03:00] Here, we can see one of the patient's humeri, which is positioned properly above the apices. In the next step, we identify the sternum anteriorly and the vertebral bodies posteriorly. The patient is positioned properly, when we can identify the anterior and posterior cortex of the sternum clearly, and we can

[00:03:30] identify the vertebral bodies clearly, posteriorly. The quality of the inspiration is difficult to assess without spirometry. However, assuming that the patient has taken a good inspiration, the outline of the 9th posterior rib should be seen above the right hemidiaphragm. In this case here, we can see to the 10th rib, how we number the ribs will be discussed in future presentations.

[00:04:00] These two x-rays, that were taken on the same patient at the same time, highlight the difference between inspiration and expiration. In expiration, the lungs will look whiter and are much smaller than in inspiration. The heart appears bigger. We see more pulmonary vessels, and without knowledge that this was an expiration film taken purposely, it would be easy to mistaken this for congestive heart failure.

[00:04:30] The exposure of the x-ray is optimum when the anatomy is clearly visible. On an adequately penetrated PA chest x-ray, the outlines of the thoracic vertebral bodies and the disc spaces should be visualized through the heart shadow and through the mediastinum. Vascular markings should be visible through the heart. When the x-ray is poorly exposed, it can be either over or underexposed. Overexposure causes a loss of anatomical

[00:05:00] detail because everything looks darker. If this occurs, some information can be extracted by increasing the brightness of the darkened areas of the image. Underexposure also causes a loss of anatomical detail. The underexposed image will look too white everywhere. To assess for proper exposure, we identify four key areas. One, within the upper mediastinum. We should be able to clearly identify the trachea

[00:05:30] and the carina. One, within the lower mediastinum, we should be able to identify the thoracic vertebra and disc spaces, and we should be able to identify the blood vessels behind the heart. We also look within the parenchyma of the mid-lungs to make sure that we can identify vascular markings. We also look in the lung bases, to make sure that we can identify the blood vessels clearly. Patient motion

[00:06:00] can decrease the quality of the x-ray because the image will be blurred. This examination shows blurring artifacts, with significant loss of sharpness, of the anatomical structures and the devices within the thorax. Artifacts should be kept to a minimum on a good quality examination. We know that, especially in critically ill patients, it's impossible to have no artifacts because of the necessity for continuous

[00:06:30] monitoring, but it's important to decrease the artifacts to a minimum where possible. Here, we have various pads on the patient that are causing considerable distraction in the interpretive process. Also, we have numerous electrocardiograph leads on both sides. Let us now evaluate several cases from the point of view of quality. This is an example of a poor quality examination.

[00:07:00] This is poor quality for several reasons. One, that the patient's chin is overlapping the upper hemithorax and is obscuring the left apex completely. We cannot identify the left clavicle so it is impossible to assess for patient rotation. Also, we have this artifact here, which is the patient's spectacles. Now, the spectacles themselves are not

[00:07:30] interfering with visualization of the heart but are distracting and can distract the viewer from more important pathology such as the pneumonia within the right upper lobe. In this case, when we assess for patient rotation, we identify the spinous processes and we see that the medial aspect of the left clavicle lies within the midline. The patient is rotated and this would account for the reason why this left

[00:08:00] hemithorax is whiter, as compared to the other hemithorax. In this case, the medial aspect of the left clavicle lies to the right of the spinous processes. This is causing considerable distortion, of the anatomical structures, within the mediastinum. In this case, we see significant artifacts from the patient's arms. Here, we have one humerus extending over

[00:08:30] the mediastinal structures. We also see a second humerus that lies within a cast. This patient had a broken upper extremity and was unable to raise the upper extremities for the lateral projection. In this case, we see significant artifacts overlying the left hemithorax, caused by the patient's arm being left on the thorax during exposure. In this case, we see artifacts

[00:09:00] related to EKG coils but also related to the fact that the examination was performed with the patient's clothing on and we see metal artifacts from the patient's brazier. In this case, the quality of the examination is very poor because of patient rotation and poor inspiration, making evaluation of the mediastinal structures as well as the right lung

[00:09:30] and both lung bases almost impossible. So, to summarize, a good quality frontal examination should include all of the thoracic structures, from the larynx to the costovertebral angles, should be taken in full inspiration with the diaphragms below the posterior 9th or 10th ribs, and we should be able to see the 10th vertebral body through the heart and see the pulmonary vessels through the heart.

[00:10:00] A good quality lateral radiograph should include all of the parts of the lungs from the sternum to the posterior ribs and include the apices and the posterior costovertebral angles.