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How to read a normal chest X-ray ???

X-ray chest normal

Chest x-ray or chest radiograph is the study of chest by imaging technology. The chest x-ray detects the pathology related to the heart and lungs. Chest radiograph gives the details about heart, lungs, airways and great blood vessels. Chest radiograph can also reveal the fluid on or around the lungs or surrounding a lung. Chest x-ray is most common imaging study that performed frequently.

How to read normal chest X-ray?

To read a normal chest x-ray first we should know about some factors like different densities, exposure factors, patient position.

Different densities of chest X-ray:

  1. Black- Air
  2. Dark grey- Fat
  3. Light grey- Soft tissue
  4. Off white- Bone
  5. Bright white- Metal

Exposure factors:

The exposure factors are the KVp and mAs. The exposure should be appropriate according to the patient. The films are neither under expose or over expose. To check this, you can see the fine markings in the lung fields to make sure that they are visible. If the fine markings are not visible then x-ray may fail to detect some diseases.

Patient position:

Patient is in straight position or sitting upright facing towards the intensifying screen. Both hands are placed at the low waist level.

Make sure there is no rotation of the patient, rotation introduces unwanted variation.

x-ray must be taken in full inspiration.

Lungs should be fully expanded. 10th posterior rib is visible if the x-ray is taken in fully inspiration. If lungs are not fully extended, we might miss some important disease.

Steps to read the chest X-ray

  1. Determine the view

First thing for reading a chest x-ray is to determine the projection/view, it is the position of patient and the x-ray tube. Views of chest x-ray are

  • Posteroanterior PA
  • Lateral
  • Anteroposterior AP

Chest (PA view) | Radiology Reference Article |

Chest PA view

For PA projection the patient is sitting upright or standing facing the IR and the tube is approx. 6 feet far from the image receptor. The x-ray is taken is full inspiration.

Chest lateral view

For making right / left lateral films patient stand or sits upright with arms raised and turns at 90° so that the desired side touch the image receptor. The x-ray beam travel from left to right for right side projection and vice versa.

Chest (AP erect view) | Radiology Reference Article |

Chest AP view

For AP projection the patient may be supine or standing depending on the case. The x-ray beam travels from the patient’s front to back. AP views are most commonly taken in portable x-rays or in the case of injure such as rib fracture.

  1. Determining image quality

There are a lot of things to check the image quality. To evaluate the image quality, remember the mnemonic R.I.P stands for rotation, inspiration and penetration.


To check whether the patient is rotated or not, look at the medial aspect of the clavicle compare the left and right medial clavicular joints to the spinous processes in the more central aspect of image. The patient should be straight-on and not rotated significantly. The distance between the medial margins of the left and right clavicles and the central spinous process should appear to be approx. equal.


The chest x-ray is taken in full inspiration i.e., the lungs field are maximally expanded. This can be check by counting posterior ribs that are visible in lung field. If you should able to count about 10th posterior rib that tells that the patient held the breath in full expiration or not.


Penetration describes the extent to which x-rays pass through the body. When the penetration is appropriate the vertebrae behind the heart are barely visible and the diaphragm can be traced up until reaching up to the edge of the spine.

Following a systematic approach

ABCD of chest x-ray

A for Air, where it shouldn’t be??

Finding air where it should not be or more commonly ruling it out remains most important uses of medical x-rays diagnosis like chest x-ray in pneumonia, pneumothorax, pneumomediastinum, pneumoperitoneum and subcutaneous emphysema are all the examples of air shouldn’t be. All of these are surgical medical emergencies and can be diagnosed by a simple chest x-ray. If the major airways like trachea are bent or deviated another example of where air shouldn’t be, it may signal of an underlying mass.

B for bones

There are present two clavicle and 12 pair of ribs. First thing is to look if any fracture deformities or missing bones are present in the both pair of clavicles and all 12 ribs. Here B is also for bony walls and soft tissues outside of the chest this is an easily overlooked part of a chest x-ray and it should be checked for swelling masses and other things.

C for cardiac silhouette and size

Cardiac silhouette is the outline of the heart seen in the frontal and lateral radiograph of chest x-ray.

Now look for the cardiac silhouette. There is an atrial appendage the atrium and the left ventricle. In chest x-rays we define feature relative to the patient so the right atrium is on the left side of the x-ray and left ventricle is on the right side measuring across a normal heart is less than 50% of the largest diameter of the ribcage measured from the inner portion of each rib, any larger and there may be cardiac pathology.

D is for diaphragm which shouldn’t be too flat but appear fairly symmetric you can assess flatness on the lateral view by estimating that the hemi diaphragm is 1.5 centimeters above the line connecting the costophrenic angle posteriorly and sterno-phrenic angle anteriorly.

Cardiothoracic ratio: the cardiothoracic ratio is the determination of enlargement of the cardiac silhouette which is commonly called as the cardiomegaly. The cardiothoracic ratio should not be more than 0.50.

Dextra cardia: The displacement of the heart to the right-side resulting mirror image of the heart in a chest radiograph.

E is for equipment

Equipment such as lines, tubes, and wires involved the life support. It is important to note whether they are in relative to other structures and whether in functional position. For example, the endotracheal tube should be in the middle of the trachea and its tip should be more than 2 centimeters from the tracheal bifurcation or that a nasogastric tube should have its tip well within the stomach.

Here checks the pleural effusion also. The pleural effusion is a common but subtle form of pathology that you can see on an x-ray. The pleural effusion is the fluid that collects at the costophrenic angle and causes blunting of the normally sharp costophrenic angle.

F is for fields

The lung field should be symmetric. There should not be any haziness, white dots or blotches while looking at lung field having a frontal and lateral x-ray allow us to determine in which lobe or which lung the abnormality is located.

G is for great vessels:

The vessels included in the chest x-ray are the superior vena cava, inferior vena cava, ascending aorta, aortic arch, pulmonary artery and descending aorta. For a normal chest x-ray all of these structures are at right location and of right size. On the left side of the heart the aortic arch should be the highest up followed by the pulmonary artery of note. Since the heart is a three-dimensional structure the atrial appendage actually sits behind the central formation in frontal x-ray. on the right side the superior vena cava, ascending aorta, right ventricle, left ventricle and inferior vena cava should all be visible. Deviation may be the result if the congenital abnormality or disease.