18 Introduction to Chest Radiology 1 (1) Flashcards Preview

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Flashcards in 18 Introduction to Chest Radiology 1 (1) Deck (19)
1

Postero-Anterior (PA) radiograph

  • The term PA 
  • Technique
  • Pros

  • The term PA
    • Refers to the direction of the X-ray beam, which horizontally traverses the patient from posterior to anterior
  • Technique
    • The patient’s anterior chest wall is placed next to the film cassette
      • Because the heart is an anterior structure
      • Placing the heart next to the cassette reduces MAGNIFICATION and increases image SHARPNESS
    • This view is taken during deep inspiration with the patient upright and 6 feet from the X-ray tube
  • Pros
    • The PA is preferred when possible because it’s quicker, the inspiration is improved, and the heart is less magnified

2

Antero-Posterior (AP) radiograph

  • When used
  • Technique
  • Portable technique

  • When used
    • Substituted for the PA when the patient is unable to stand or sit
  • Technique
    • The patient’s back is placed against the film cassette
    • The X-ray beam traverses the patient from anterior => posterior
  • Portable technique
    • When a patient is unable to be moved, an AP radiograph may be performed with portable equipment
    • Because of low ceilings and portable equipment, the AP is usually taken at a distance of 3 feet
    • Compared to the PA, this increases magnification and decreases image sharpness

3

Left Lateral CXR (LL CXR)

  • Technique
  • Right vs. left

  • Technique
    • The left side of the chest is placed against the film cassette
    • The X-ray beam traverses the patient from right to left
  • Right vs. left
    • We perform a LEFT LATERAL CXR rather than a right lateral because the heart is on the left
    • This places the heart as close as possible to the film cassette, thus decreasing cardiac magnification and increasing sharpness
    • The LL CXR also gives a better look of the lung (left lower lobe) behind the heart

4

What tissue densities we can see on the radiograph

  • In order off increasing density
  • On the radiograph, anatomic structures are recognized by their...

  • In order off increasing density
    • Air - lungs
    • Fat - in breast and subcutaneous tissues and around muscle
    • Water (soft tissue) - heart, muscle, and blood
    • Metal or Ca - bone, metalli chardware, and contrast agents
  • On the radiograph, anatomic structures are recognized by their...
    • Dfferent densities
    • Different abilities to absorb or attenuate the X-ray beam

5

Film exposure

  • Traditional radiography has been performed with...
  • Computed radiography (CR)
  • Direct radiography (DR)

  • Traditional radiography has been performed with...
    • Film-screen cassettes
  • Computed radiography (CR)
    • Uses storage phosphor plates in place of film-screen cassettes
    • Enables filmless acquisition of radiographs using existing X-ray equipment
  • Direct radiography (DR)
    • Group of technologies that can indirectly or directly convert X-ray intensity into electric signals

6

Film exposure

  • When radiographic film is exposed to radiation
  • An area of film exposed to more radiation will be...
  • The lung
  • Bone

  • When radiographic film is exposed to radiation
    • The silver ion in its emulsion precipitates
    • The color of silver ion is BLACK
  • An area of film exposed to more radiation will be...
    • Blacker than an area that receives less
  • The lung
    • Contains mostly air
    • Will be blacker than bone
  • Bone
    • Has greater density and ability to absorb or block the X-ray beam
    • Blocks more radiation from reaching the film
    • Less silver ion precipitates
    • The image of bone is white

7

Film exposure

  • With an optimally exposed image, the disc spaces of the spine are... 
  • When we accidentally over-expose (over-penetrate) an image,...
  • In contrast, when we use insufficient exposure or when a patient is obese,...
  • Both over- and under-exposure...

  • With an optimally exposed image, the disc spaces of the spine are...
    • Barely perceptible through the heart
  • When we accidentally over-expose (over-penetrate) an image,...
    • It receives excess radiation
    • All structures will appear too black
  • In contrast, when we use insufficient exposure or when a patient is obese,...
    • The image is under-exposed (under-penetrated)
    • The image then receives too little radiation, very little silver ion is deposited, and all structures will be too white
  • Both over- and under-exposure...
    • Limit the detection of pathology

8

The silhouette sign

  • The silhouette sign
  • Normally, when two substances of water density are in anatomic contact,...
  • When the lung (air density) is filled in with pneumonia (water density),...

  • The silhouette sign
    • The loss of the normal interface between two structures of different density
      • Air in lung
      • Soft tissue of the heart
    • Helps us identify and localize pathology, especially in the thorax
  • Normally, when two substances of water density are in anatomic contact,...
    • They cannot be differentiated from each other
    • Their interfaces cannot be perceived
    • Blood within the lumen of the heart cannot be distinguished from contiguous heart muscle
    • It all looks “white” on radiography
  • When the lung (air density) is filled in with pneumonia (water density),...
    • The normal air – water interface between the lung and the adjacent heart border will be obscured
    • The heart border is obliterated or “silhouetted” [sic] by the pneumonia

9

How to display the chest radiograph

  • We display the PA or AP as if we are facing the patient
  • The patient’s right is on our left, and his left is on our right
  • We place the lateral CXR as if the patient is facing towards our left
  • The films will be labeled with side
  • Turn off the overhead lights and always get comparisons!

10

Chest CT: computed axial tomography, aka CAT scan and CT

  • CT
  • Contrasts

  • CT
    • Technique of cross-sectional imaging of the body using computer processing & image reconstruction
    • Compared to conventional radiography, CT is superior in depicting tissue contrast and in identifying anatomic location and pathology
    • The patient is placed in the scanning gantry and helical or conventional axial images are obtained
  • Contrasts
    • Intravenous iodinated contrast and enteric contrast (barium) are frequently used to enhance definition of vessels and bowel and to assess pathologic processes
    • Because contrast agents have very high attenuation (and block the X-ray beam), structures containing contrast will appear white rather than shades of gray

11

Chest CT: computed axial tomography, aka CAT scan and CT

  • Helical (spiral) CT 
  • Multi-detector CT (light speed) 

  • Helical (spiral) CT
    • Provides volumetric data acquisition during a single breath hold as the patient is moved continuously through the scanning gantry
    • This results in a helix of raw data from which planar images may be generated without gaps in data
    • Data may be evaluated at narrow reconstruction intervals, which facilitates multi-planar and 3-D reconstructed images
  • Multi-detector CT (light speed)
    • The newest helical CT scanner
    • Has up to 64 detectors that collect 64 helices per gantry rotation
    • Advantages
      • Routine thin slice acquisition
      • Ability to retrospectively change image thickness
      • Increased extent of body imaged during one scan or one breath-hold
      • Extremely fast scan times
    • All CT scanners at UPMC are multi-detectors

12

Chest CT: computed axial tomography, aka CAT scan and CT

  • Older conventional axial CT
  • High resolution CT (HRCT)

  • Older conventional axial CT
    • A single axial image is acquired, then the patient is moved to the next slice location and the next image is obtained
    • It usually takes 2 or 3 breath-holds to complete a conventional chest CT, which increases the risk of motion artifact
  • High resolution CT (HRCT)
    • 1 – 2 mm thin axial images of the lungs are obtained at 10 to 30 mm intervals
    • An edge-enhancing algorithm is applied, which sharpens definition of the interstitium

13

CXR search pattern

  • Technical 
  • Bones
  • Soft tissues
  • Abdomen

  • Technical
    • First assess patient position, the degree of inspiration, and the film’s exposure
  • Bones
    • Inspect the bones (shoulders, ribs, and cervical and T-spine) for alignment, fractures, destruction
  • Soft tissues
    • Evaluate the soft tissues (breasts, pectoralis muscles, etc.) for symmetry and lesions
  • Abdomen
    • While the abdomen is under-penetrated on the CXR, look for free air, dilated bowel, abnormal calcification, and masses

14

CXR search pattern:
Heart

  • Location
  • Parallel pumps
  • Size
  • Borders

  • The heart lies to the left of midline in the mediastinum (the central compartment of the thorax)
  • It consists of two parallel pumps
    • The right heart is a low-pressure system that delivers deoxygenated blood from the body to the lungs
    • The left heart is a high-pressure system the pumps oxygenated blood from the lungs to the body
  • The heart size is normally less than half the widest diameter of the thorax
  • The heart borders discernable on the PA radiograph are the superior vena cava and right atrium on the right and the aortic arch, main pulmonary artery, and left ventricle on the left

15

CXR search pattern:
Lungs

  • Left vs. right lung
  • Right lung lobes
  • Left lung lobes
  • Normal lungs

  • The left lung is smaller than the right because the heart is on the left
  • The right lung has three lobes
    • Right upper lobe (RUL)
    • Right middle lobe (RML)
    • Right lower lobe (RLL)
  • The left lung has two lobes
    • Left upper (LUL)
    • Left lower lobe (LLL)
  • Normal lungs
    • Should be clear and more lucent (black) at the bases where lung volumes are the greatest
    • Consists predominantly of air and doesn’t normally produce its own separate shadow
    • Interstitial or vascular markings are not normally seen in the periphery of lung

16

CXR search pattern:
Pleura

  • Pleura 
  • Parietal pleura
  • Visceral pleura
  • Fissures
  • Left major fissure
  • Right major fissure
  • Minor fissure

  • Pleura
    • Normally 1mm thin
  • Parietal pleura
    • Lines the diaphragms, chest wall, and mediastinum
  • Visceral pleura
    • Covers the lobes of the lung
  • Fissures
    • Made up of 2 layers of visceral pleura
    • Seen as a pencil thin line when tangent to the X-ray beam
  • Left major fissure
    • More vertical
    • Separates the LUL from the LLL
  • Right major fissure
    • More oblique
    • Separates the RUL and RML from the RLL
  • Minor fissure
    • Divides the RUL and RML

17

CXR search pattern:
Trachea and bronchi

  • Trachea
  • Left main bronchus
  • Right main bronchus
  • Smaller bronchi

  • Trachea
    • Lies in the mediastinum
    • Displaced slightly to the right by the left-sided aortic arch
    • Divides at the carina (T4-6) into the L & R main bronchi, which continue into the lung
  • Left main bronchus
    • Longer (5 cm), inferior, and more horizontal than the right
    • Divides into LUL and LLL bronchi
  • Right main bronchus
    • Shorter (2.5 cm) and more superior and vertical
    • Divides into the RUL and bronchus intermedius, which then divides into RML & RLL bronchi
  • Smaller bronchi
    • Not normally detected in the lung unless diseased

18

CXR search pattern:
Vessels

  • Pulmonary arteries (PA’s) 
    • General
    • Right pulmonary artery (RPA) 
    • Left pulmonary artery (LPA)
  • Pulmonary veins

  • Pulmonary arteries (PA’s)
    • General
      • Parallel the bronchi
      • Vertically oriented
      • Divide into upper and lower branches
    • Right pulmonary artery (RPA)
      • Passes in front of the bronchi
    • Left pulmonary artery (LPA)
      • Arches over the L main bronchus
      • More superiorly oriented than the RPA
  • Pulmonary veins
    • More horizontal than the PA’s
    • Do not parallel the bronchi
    • Form a single trunk from each lobe of the lung
    • Drain into the left atrium
    • Inferior pulmonary veins form the lowest part of the hila

19

CXR search pattern

  • Hila
  • Left hilum
  • Right hilum
  • Mediastinum 
  • Right vs. left diaphragm

  • Hila
    • Where the pulmonary arteries and veins and main bronchi enter the lung
    • The attenuation of the hilum is made up mainly of the pulmonary artery and vein
    • The right and left hila have the same height in 2% of normal CXRs
  • Left hilum
    • Superior to the right in 98% of normal CXRs
  • Right hilum
    • NEVER normally higher than the left
  • Mediastinum
    • Central compartment of the chest
    • Lined by the mediastinal parietal pleura
    • Major mediastinal structures: the heart, tracheobronchial tree, and esophagus
  • Right vs. left diaphragm
    • Right diaphragm is usually slightly higher than the left
    • In 3% of cases, the left is higher but only by 1 cm
    • A scalloped contour is common

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