Cardiopulmonary Imaging

Cardiopulmonary Imaging

• Imaging studies are important in diagnosing patients with cardiopulmonary disease
• Respiratory Care Practitioners (RCP's) use these images to understand and treat patients
• Chest radiographs are a popular, inexpensive, and reliable imaging method

Terminology

• Radiolucent areas appear dark, indicating the presence of air, which is normal
• Radiodense/opacity or radiopaque areas appear white, indicating solid or fluid-filled structures, normal for bones and organs
• Fluid, mass, bones, and dense liquids like pneumonia can cause radiodensity/opacity
• Infiltrates are ill-defined radiodensities that are plate-like, indicating atelectasis
• Consolidation appears as a solid white area, suggesting pneumonia or pleural effusion with excessive fluid in the pleural space
• Hyperlucency refers to extra pulmonary air, seen in conditions like COPD, asthma exacerbation, and pneumothorax
• Manage hyperlucency by considering LVN, antileukotrienes, or systemic steroids such as Magnesium or albuterol if O2 regimens are ineffective
• Vascular markings include lymphatics, vessels, and lung tissue; they increase with CHF and are absent with pneumothorax, spreading throughout the lungs
• Diffuse indicates a spread throughout, seen in atelectasis or pneumonia
• Opaque areas indicate fluid or solid consolidation
• Bilateral affects both sides, while unilateral affects one side
• Fluffy infiltrates are diffuse whiteness with a butterfly/batwing pattern, indicating pulmonary edema
• Patchy infiltrates are scattered densities, suggesting more severe atelectasis
• Platelike infiltrates are thin-layered densities, indicative of atelectasis
• Ground glass or honeycomb patterns are reticulogranular and uniformly distributed through both lung fields, seen in ARDS and fibrosis

Radiographic Positions

• In Posteroanterior (PA) position, X-rays pass from back to front with the image receptor at the front; most common and ideal position
• Lateral views, abbreviated "Lat”, are orthogonal views to frontal views
• Right Anterior Oblique position requires the patient to be rotated 45 degrees towards the right, with the right side of the chest against the image receptor
• Anteroposterior (AP) position involves X-rays passing from front to back
• Anteroposterior Supine position is when the patient lies flat on their back with the X-ray going from front to back and the detector underneath
• Right Lateral Decubitus position involves the patient lying on their right side with the body's longitudinal axis perpendicular to the imaging table

Chest X-Ray Interpretation

• The heart should be less than half the diameter of the chest on an X-ray
• Cardiomegaly is indicated when the heart is greater than half the chest diameter and may signify potential heart failure

Different Densities

• Air appears black because it absorbs the least X-rays, resulting in dark shadows (radiolucent)
• Bones absorb the most X-ray energy, resulting in white shadows (radiopaque)
• Fat, soft tissue, and fluid appear in varying degrees of gray

PA Chest Film

• Involves the X-ray beam passing from posterior to anterior (PA) with the film against the patient’s chest, usually done standing in the radiology department
• Results in high-quality images with minimal heart shadow magnification

AP Chest Film Characteristics

• The heart appears larger
• Typically taken with a portable X-ray machine
• The X-ray source is in front of the patient, and the film is behind
• Often more difficult to read due to lower quality compared to PA films
• The heart shadow is more magnified because the heart is closer to the X-ray source and farther from the film
• Rotation of patients is more likely

Technical Factors

• The diaphragm is elevated in the supine position
• The heart appears larger on an AP film because it is more anterior
• Penetration refers to the amount of X-ray exposure
• Overpenetrated films appear too black, while underpenetrated films appear too white

Indications for a CXR

• Unexplained dyspnea and severe persistent cough
• Hemoptysis and fever with sputum production
• Acute severe chest pain and positive TB skin test
• Essential after ETT placement, pulmonary artery catheter placement and central venous pressure catheter
• Elevated or changing plateau pressure during mechanical ventilation
• Sudden decline in oxygenation and suspected consolidation or pneumonia

Approach to Reading Chest Films

• A disciplined approach is needed
• Do not focus only on the obvious; less obvious items can be important
• Ensure the film matches the patient's name
• Evaluate the technical quality of the film, including patient position and X-ray penetration
• Systematically assess all anatomical structures in a prescribed series of steps

Important Factors to Note

• Pulmonary embolism may appear normal on X-rays
• Chronic COPD patients may also appear normal
• There may be a lag time between the clinical condition and X-ray findings
• Example: Aspiration pneumonia might take 12-24 hours to show with fever and cough

Assessment

• A = Airways (trachea midline, centered, shifting?)
• Tracheal shifting is a very high concern
• B = Bones and soft tissues (vertebral bodies, spinal process)
• C = Cardiac Silhouette & Mediastinum (enlarged, deviated)
• D = Diaphragm (gastric bubble, flattening, right side slightly higher than left due to liver)
• E = Effusion (pleura), lateral decubitus to rule out effusion
• F = Fields, Lung fields, look for lines, tubes, and signs of previous surgeries
• Chest films should be be on full inspiration; otherwise it may make the heart appear larger and airway with volume loss

Assessment of Structures

• Assess chest wall and mediastinum for symmetry
• Look for rib fractures, bone changes, heart size, and presence of free air or fluid
• Evaluate lung size, density, and symmetry, as well as lung edges in frontal and lateral films
• Note vascular markings, presence of free air or fluid, consolidation, and infiltrates
• In pneumothorax, the trachea will shift away from the infected lungs

Hydrothorax / Pleural Effusions

• Often referred to as pleural effusion
• A blunted costophrenic angle on chest X-ray suggests pleural effusion
• Around 200 ml of pleural fluid will blunt the costophrenic angle
• Lateral decubitus is the best chest X-ray view for detecting small pleural effusions
• Empyema is pus in the pleural space with pus-filled pockets
• A flat diaphragm indicates an increased presence of air

Pneumothorax

• Refers to a collection of air in the pleural space
• Occurs spontaneously, with trauma, or with invasive procedures
• Can occur with mechanical ventilation, known as barotrauma
• Causes the lung margin to pull away
• Presence of air is better visualized by comparing inspiratory vs expiratory films

Tension Pneumothorax

• Represents a serious medical emergency
• Occurs when air within the pleural space is under pressure
• Air accumulates during inspiration but cannot exit during exhalation
• Chest film shows a shift of the mediastinum away from the pneumothorax
• Requires immediate decompression with a chest tube or needle aspiration of trapped air
• Can lead to cardiac tamponade and hemodynamic collapse
• A pigtail catheter may be needed

Pulmonary Infiltrates

• Indicate pus or fluid inside the Lungs
• Fluid indicates pulmonary edema and pus indicates pneumonia
• Alveoli fill with watery fluid (edema), pus (pneumonia), blood (alveolar hemorrhage), or fat-rich material (alveolar proteinosis)
• These are often seen as white shadows in the lung
• Air bronchograms occur when air bronchi (dark) are made visible by opacification of surrounding alveoli (gray/white)

Pulmonary Edema

• Commonly due to left heart failure on chest radiograph
• Left heart failure causes enlargement of pulmonary blood vessels in the apex of the lung (cephalization)
• Kerley B-lines are often seen with pulmonary edema due to left heart failure
• Chest radiograph often shows enlarged heart and pleural effusion with CHF

Interstitial Disease

• Chest radiograph usually shows diffuse, bilateral infiltrates
• Infiltrates may look like scattered ill-defined nodules
• Many different types of ILDs with idiopathic pulmonary fibrosis and sarcoidosis being the most common forms
• "Honeycomb" appearance can occur with idiopathic pulmonary fibrosis, collagen vascular disease, asbestosis, chronic hypersensitivity pneumonitis, and medication induced causes (amiodarone)
• ARDS show ground glass appearance, honeycomb pattern, and diffuse bilateral radiopathy

Atelectasis

• This is defined as a collapsed or airless condition of the lung
• Common finding on chest radiograph, especially in postoperative patient
• When located to a subsegmental portion of the lung, it is called "plate atelectasis"
• Lobar atelectasis occurs when a major bronchus is obstructed by a mucus plug, tumor, or foreign body
• Signs of volume loss include elevation of the hemidiaphragm and shift of helium toward the affected side
• Transcription may read "infiltrate," describing an ill-defined radiodensity

Hyperinflation

• Commonly seen with emphysema
• Other signs include flattening of hemidiaphragms, large retrosternal airspace, narrowed mediastinum, and increased AP diameter
• Emphysema causes loss of visible blood vessels in the lung

Signs

• "Thumb sign" seen with Epiglottitis is diagnosed via a lateral neck image
• "Steeple sign" seen with Croup

Catheters, Lines, Tubes

• Chest radiograph is obtained after placement of endotracheal tube, CVP line, or pulmonary artery catheter
• Film confirms proper placement
• Tip of the endotracheal tube should be 2-6 cm above the carina with the patient's head in neutral position, below the vocal cords, at the level of the aortic knob or notch, below the clavicles
• Pacemaker should be in the right ventricle
• Pulmonary artery catheter in the right lower lung field
• Chest tubes are in the pleural space surrounding the lungs
• Nasogastric and feeding tubes should be in the stomach 2-6 cm below the diaphragm

Cat Scan (CT)

• CT is very helpful in certain situations and visualizes structures cross-sectionally with great detail up to 2 mm inside the lung
• CT scanning creates images that appearing like “slices” of patient’s chest (5-7 mm thick)
• Conventional CT scanning is used to evaluate lung nodules & masses, great vessels, mediastinum, and pleural disease
• Iodinated contrast helps to distinguish the blood vessels from the soft tissue structure (Dye’s can cause fatal response)

High Resolution CT (HRCT)

• This scanning examines 1-mm slices of lung, producing greater lung detail
• Ideal for evaluating diffuse parenchymal lung diseases, interstitial lung disease, emphysema, or bronchiectasis
• If a patient has suspected pulmonary embolism, then a CT will be requested; CT scans are the gold standard for diagnosing pulmonary embolism along with strokes

Magnetic Resonance Imaging (MRI)

• Used to confirm brain dead
• Uses radio waves instead of X-rays to realign hydrogen nuclei
• Used to image mediastinum, hilar regions, and large vessels in the lung
• Cannot be used in patients with pacemaker, tracheostomy tube safety, or metal objects; limitations in chest medicine

Ultrasound

• Images are created by detecting sound waves that bounce back from tissues after high frequency sound waves are passed through the body
• Portable, but gives a limited ultrasonic evaluation of the lung
• Commonly used to guide insertion of central and arterial catheters, to detect and quantify pleural effusions, or during codes to monitor heart

Ventilation Perfusion Scan (V/Q)

• Beneficial for identifying PE
• For the perfusion part, radioactive particles (albumin tagged with radioactive iodine) are injected into a vein: these particles are large and cannot get through the lung capillaries and get trapped
• Areas of high flow will have few particles and appear “cold” or clear on the film
• For the ventilation part, a radioactive gas (xenon) is inhaled