X-ray Interpretation

X-rays account for > 80% of all diagnostic studies ordered

Chest x-rays and extremity films are the 2 most commonly ordered x-rays

X-rays are meant to be used in combination with the patient’s history and physical examination to assist with an accurate diagnosis

X-rays are made when an x-ray beam passes through an area on the patient producing different shadows on the films

The amount of shadowing is determined by the type of material or tissue the beam is flowing through

Denser structures such as bone absorb more x-ray whereas air (least dense of all) absorbs very little

4 Basic Densities or Shades
4 basic shades/densities on a film

Air: does not absorb much radiation
Air in the lungs – x-ray appears dark

Fat: absorbs some x-ray beam
Appears gray on x-ray
Darker than muscle or blood

Water (blood and soft tissue):
Lighter than fat

Bone: Appear almost white on x-ray

**The following also appear white:
Contrast material

brightness or any area of whiteness on an image

blackness on an image

anything visible on an image: any density or lucency

visible demarcation between a density and a lucency

thin density with lucency on both sides

Any edge or line

another term for an edge

Two dimensional look at the body (which is 3 dimensional)

Therefore, multiples views of an area are often standard
– This is why PA and lateral views are often performed on the chest (in an upright patient)
– Provides additional view that may identify something not visible on a single view

PA View
Patient’s chest is against the film

X-ray beam passes from posterior region (patient’s back) to the anterior region (chest)

X-ray machine is approximately 6 feet away

Great view of things that sit anterior:
This view is better to see the heart (because heart is anterior)

Chest radiographs
PA (posteroanterior)- X-ray beam entered the patient posteriorly and exited anteriorly

AP (anteroposterior)

Left lateral decubitus

These terms refer to the direction in which the x-ray beam traversed the patient on the way to the film

Indications for Chest X-ray
Based upon your history and physical examination, a chest x-ray may be ordered to assess to:
Detect and assess lung disease: Pneumonia, CHF, COPD, Cancer

Assess for chest trauma

Placement of tubes/devices

Basic Information
Regarding Chest X-rays
The most common chest film is a PA film – Performed at a distance of 6 feet

AP is often done on hospitalized patients (portable or supine film)

If the clinician just writes for a Chest x-ray: Lateral view is also routine
– Left side is against the cassette
– Lateral view is essential for any lesions behind the heart, mediastinum, or diaphragm as these are often missed on a PA film

Chest X-rays are performed with the individual in inspiration –> This causes the hemidiaphragm to descend to the level of the 10th posterior ribs

This is important because…if the diaphragms are at the 7th ribs posteriorly, the chest is hypoinflated

Conversely, if the hemidiaphragms are at the 12th rib posteriorly, the chest is hyperinflated

When would you
order an
expiration film?
Seems to be good for identifying focal air trapping from:
Partial bronchial obstruction
Foreign body aspiration

Clinical pearl: if you hear a unilateral wheeze that does not clear with coughing – an expiratory film may be a good idea

Normally, a deflated lung will appear whiter while the obstructed lung will appear unchanged

Systemic Approach
to Interpretation:
Step 1
PA or AP film is hung on the view box like you are facing the patient from the front

Start reading the x-ray by looking at the least important areas first

Then move to the most important areas; the reason you ordered the x-ray in the first place

**Verify name, age, and date of birth**

Systemic Approach
to Interpretation:
Step 2
Technique utilized- PA, AP, lateral
– PA and lateral preferred (PA clearer)

Position of the patient- Upright, supine, decubitus, lordotic
– Upright preferred

Inspiratory Effort- Normal, hyperinflated, hypoinflated


Helpful when trying to remember your systematic approach to chest x-ray interpretation

Are There Many Lung Lesions?
Thorax (soft tissues and bones)
Lung (unilateral)
Lungs (bilateral)

Start With The Abdomen
Start in the right upper quadrant

Scan across the abdomen

Normally, you will see the following:
Stomach bubble
Splenic flexure of the colon
Diaghragm (right diaphragm is higher than left) Spleen may or may not be visible

Usually dome shaped although some individuals have “polyarcuate” diaphragms –> These look like numerous domes together instead of 1 dome

This is a normal variant that is often mistaken for a diaphragmatic tumor

Right diaphragm is higher than the left

The diaphragms form acute angles with the chest wall (costophrenic angles)

If these angles become blunted, consider pleural fluid

Move to the Right Lung Base
Start with the right base, looking at:
Soft tissues (Muscles, breasts)

Chest wall

• Anterior ribs descend from lateral to medial
• Posterior ribs descend from medial to lateral
• Only the upper ribs are completely seen on x-ray

Shoulder girdle (scapula)

Scan up to the clavicle

Then work down the left lung to the base

Compare right to left

Look for:
Right breast
Anterior ribs
Posterior ribs
Left breast

Little differentiation between various structures

Start with an overall look at the area for any abnormalities with contour, such as widening

Start with the trachea and work downward
– Trachea
– Carina
– Aortic knob (arch)
– Ascending aorta
– Descending aorta
– Heart
– Hilum

Now, Look at the Lungs
Since most chest x-rays are ordered to look at the lungs, these are saved for last

We always need to look at the lungs twice when examining the x-ray

First examination is looking at each lung individually

Second examination is a comparison between the right and left lung

Also…use this as an opportunity to look again at the costophrenic angles and the hilum

Lateral Films
Use the same approach to lateral films:

Lung contains alveoli (air sacs)

Air sacs are supported by structures such as the vessels, lymphatics, bronchi and connective tissue

The alveoli and the supporting structures are called the interstitium

On the chest x-ray, the pulmonary vessels are our only look at the interstitium as everything else is radiolucent or black (invisible)

Pulmonary Vessels
Branch and taper as they progress out to the periphery

Therefore, they are not visible in the outer 1/3 of the lung

If a disease affects the interstitium (alveoli, vessels, bronchi, lymphatics), the tissue around the pulmonary vessels will thicken and become more visible in the periphery of the lung

Fluid or Tissue
If fluid or tissue (blood, edema, tumor, mucus) fills the alveoli, the lungs will become radiodense and the interstitial markings will become less visible

Silhouette Sign
Probably, one of the most important things to look at with a chest x-ray

Helps to determine the location of an abnormality in relation to the normal structures (helps us to diagnose and localize lung disease)

Two substances of the same density can not be differentiated from each other on x-ray

This phenomenon, the loss of the normal radiographic silhouette (contour) is called the silhouette sign

Right middle lobe
lies in contact with the right heart border

Therefore, if there is a consolidation of the RML-the right heart border will be obscured

Right Lower Lobe
This lobe sits on the diaphragm

So…if an individual has a right lower lobe pneumonia, the right diaphragm will be obscured

Left Lower Lobe
This lobe sits on the left diaphragm and is direct contact with the descending aorta

So…if an individual has a left lower lobe pneumonia, the left diaphragm and descending aorta will not be visible

Upper Lobes
Right upper lobe consolidation will cause a silhouette sign of the right heart border and the right trachea/lung

Left upper lobe consolidation will obscure the left atrium, aortic knob and the anterior and middle mediastinum –> It can also obscure the proximal descending aorta

Normally, a chest x-ray with an asthma flare is not necessary, unless you are concerned regarding pneumonia or an aspiration

If an individual is having an acute asthma flare, you may see the following abnormalities on chest x-ray
– Hyperinflation
– Flat diaphragms
– Prominent Interstitial Markings (scarring)
– Occasionally, you will see thickened bronchial walls

Most patients with asthma have normal x-rays

Chest x-ray: only detects moderate-severe COPD


Superior aspect of the hemidiaphragm is often
depressed down to the level of the posterior 12th rib

Flattening of the diaphragms

Blunting of the costophrenic angles

Increased AP diameter (seen best on the lateral view)

May also see bullae due to the destruction of the alveoli

Diagnosis of pneumonia is usually made clinically :Fever, cough, myalgias, pleuritic pain, anorexia

Physical examination findings: crackles, dullness to percussion, egophony, bronchophony or whispered pectoriloquy

Clinician uses the x-ray to confirm suspicions

Most pneumonias produce lobar, segmental or patchy alveolar infiltrates –> To identify location, PA and lateral chest x- rays are often necessary

Right Middle Lobe Pneumonias
Medial or lateral segments or both

Right medial segment – may obscure the right heart border on the frontal view

On lateral view: triangular density radiating from the hilum toward the anterior and inferior aspect of the chest

Obscures the right cardiac border

Right & Left Lower Lobes
Often visualized with one of the following 3 methods:
May obscure right or left hemidiaphragm on frontal view

Lateral view: looks as if it is behind major fissure OR

You can utilize the spine sign: normally: vertebral bodies of thoracic spine get darker as you proceed lower in the chest

If the vertebral bodies get darker then start to lighten, consider lower lobe infiltrate (to determine left or right lobe-you then need a frontal view)

Spine Sign
You can utilize the spine sign: normally: vertebral bodies of thoracic spine get darker as you proceed lower in the chest

If the vertebral bodies get darker then start to lighten, consider lower lobe infiltrate (to determine left or right lobe-you then need a frontal view)

Right lower lobe pneumonia
diaphragm is obscured on lateral view

Mild or localized volume loss of the lung

Not always real easy to see

On some occasions, a “line” will be visible and will mark the lung

Other times, we must use other findings to confirm our suspicions

Air in the pleural space

Usually the result of trauma but can be spontaneous

Remember, the pleural space should not be seen normally

When air enters the pleural space, because the person is upright with the chest x-ray, the most common place for a pneumothorax is the right and left upper lobes

Appears as a thin white line, adjacent to the ribs where normally no lung vascularity should be seen

Represents the visceral pleura that has been separated from the parietal pleura by air

Remember…if you are concerned about a pneumo, an expiration chest film will help to identify a small pneumo

Expiration view causes the lung to become more dense and smaller, whereas the pneumo size doesn’t change. This makes the pneumo appear larger

Pleural Effusion
Fluid in the lung

Blunting of the right costophrenic angle

Fluid seen on lateral view

Solitary nodule is often 1 of 2 things: Granuloma or Lung cancer

Characteristics of the Nodule
Nodule characteristics
– Round (likely to be a granuloma)
– Regular or irregular (irregular – cancer)
– Calcification within the nodule (central – granuloma)

Compare it with old films
– Nodule that has remained unchanged x 2 years is considered benign

Usually < 0.5 cm Easily seen Quite dense Solitary Often found in an individual who is < 40 years of age

Lung Cancer
Usually picked up with a chest x-ray that is done for other reasons i.e. pneumonia, shortness of breath

– Irregular
– 0.5 cm or larger
– Poorly defined borders– Shaggy appearance (carcinoma)
– Asymmetric lesion
– Cavitated

Usually seen on x-ray as a large mediastinal mass or hilar adenopathy

This is detected by looking at the width of the heart at its widest point

It should be less than 1⁄2 of the thorax at its widest point from the middle of the spine to the inner ribs

Congestive Heart Failure
Usual findings
– Cardiomegaly
– Redistribution of the pulmonary vascularity

Normally, vessels in the lower lobe are more prominent than in the upper lobe –> With CHF, they are equally prominent

Kerley B lines
• Small, horizontal lines are seen in the periphery of the lung
• Represent fluid in the interlobular septa

As CHF progresses,
The hilum becomes indistinct
It is usually symmetric
Called “Bat Wing” Infiltrate
Pleural effusions may become present
This is seen on x-ray by a blunting or an obscuring of the costophrenic angles

Why Would You
Order Abdominal Films?
Acute abdominal pain

Sudden onset of abdominal pain: bowel perforation, ruptured ectopic pregnancy, ovarian cyst, aneurysm, or ischemic bowel

Gradual onset: appendicitis, cholecystitis, bowel obstruction

Films: Chest x-ray and Abdominal film (upright and supine)

Ultrasound: if considering ectopic, cholecystitis, ovarian pathology

Kidneys, ureter, bladder: most common abdominal imaging study

This film will allow you to see the bony structures (hips, vertebrae); lung bases, soft tissues (psoas muscles, liver, kidneys) and gas patterns

Quite common

RUQ: Single or multiple calcifications are often gallstones or kidney stones
– Posterior view helps to differentiate between the two (gallstone – anterior)

LUQ: almost always splenic in nature
– However, appearance can provide clues as to the etiology
– Multiple, small: histoplasmosis
– Serpiginous: splenic artery calcification – Rounded: splenic artery aneurysm

Pancreas: pancreatitis
– Lie in close proximity to the L1 – L2 vertebrae and extend to the left
– Do not always count on them being present – CT is a better test for pancreatitis

Rarely seen but when present, is fascinating

Horizontal band of calcifications going across the upper abdomen

CT is needed

Mesenteric lymph nodes –> infection

Popcorn-shaped calcifications

Right mid-abdomen

On an upright view, these calcifications drop substantially

Calcification in the appendix

Use history to make diagnosis in combination with this film and a helical CT

Supine film

Dilated small bowel loops

No definite gas in the colon

Consider appendicitis vs. bowel obstruction

Small Bowel
Plain films can be very useful when looking for abnormalities of the small bowel

Small bowel: central location and thin mucosal markings that extend like stripes across the entire lumen make identification easy –> hese stripes (valvulae) look like a set of thick, stacked coins

Small bowel is < 3 cm in diameter Gas pattern plain film is helpful

Small Bowel Obstruction
Large amount of dilated small bowel

Recognized as small bowel by regular mucosal pattern of the valvulae extending across the lumen

Looks like a set of thickly stacked coins

Kidney Stone
Normal kidney: 13 cm in size on x-ray (smaller on ultrasound)

Plain film is not your choice of diagnostic tests (either IVP or spiral / helical CT)

Silhouette Sign MOST useful sign in chest radiographs Determines the abnormality in relation to normal structures Loss of normal border indicates abnormality contiguous with that structure Possible to diagnose disorders such as pulmonary consolidation or collapse even when one is …

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