DIAGNOSTIC IMAGING METHODS

HISTORY

1895-Wilhem Roentegen

Produced the 1st X ray film image of his wife’s hands

X RAY

Form of radiant energy similar to visible light

Has very short wavelength

Penetrates many substances that are opaque to light

Produced by bombarding a tungsten target with an electron beam with an x-ray tube.

FILM RADIOGRAPHY

Utilize a screen film system within a film cassette ( x-ray detector)

COMPUTED RADIOGRAPHY (CR)

Filmless system

No processing

Produces A DIGITAL RADIOGRAPHIC IMAGES

DIGITAL RADIOGRAPHY

Filmless system

Substitutes a fixed electronic detector on charge-coupled device for the film screen cassette or

phosphor imaging plate.

CONVENTIONAL TOMOGRAPHY

Provides radiographic images of slices of the patient

Done by simultaneously moving both x-ray tube and x-ray detector around a pivot point center

to the patient

Improved detail

FLUOROSCOPY

Real time radiographic visualization of moving anatomic structures

Useful in evaluating motion such as gastrointestinal peristalsis, movement of diaphragm during

respiration and cardiac action

PRINCIPLES OF INTERPRETATION

5 basic radio densities

Air density

Fat density

Soft tissue density

Bone density

Metal/contrast agent density

Air attenuates very little of the x ray beam-most are transmitted-> black on radiograph

Bone, metal, contrast agent attenuates a large proportion of x ray beam-> white on radiograph.

Fat and soft tissue – intermediate amt. of x ray beam-> shades of gray on radiograph

Anatomic structures are seen when outlined by tissues.

Contrast agents- suspensions of iodine or barium

Disease states may obscure normally visualize structures by silhouetting their outline.

CROSS SECTIONAL IMAGING TECHNIQUES

CT, MR, AND ULTRASOUND

Produced 2 dimensional image

Resulting image is made up of pixels which represent a voxel of patient tissue

COMPUTED TOMOGRAPHY

Displays each splice separately

No superimposed blurred structures seen.

Hounsfield unit (H) scale

o Air:1,000H

o Lung tissue :-400 to -600 H

o Fat:- 60 to -100 H

o Water: value of 0 H

o Soft tissue:+40 - +80 H

o Bone:+400 to + 1000 H

Most CT units allow slice thickness between 0.5 to .10mm

Advantages of CT compared to MRI:

o Rapid scan acquisition

o Superior bone detail and demonstration of calcification.

TYPES OF CT SCAN:

Conventional CT (non helical)

- Obtain image data one slice at a time- one slice per breath hold.

- Requires at least 2-3x the total scanning time of helical CT.

Helical CT (spiral)

- Improved speed of image acquisition.

- Improved visualization of small lesions.

- Scans entire abdomen, pelvis in 2-3 breaths.

Multidetector helical CT

- Latest technical advance in CT imaging

- Obtains multiple slices per tube rotation

- 5-8x faster than single slice helical CT.

- DA: radiation dose, 3-5x higher than single slice CT.

Contrast administration in CT

- Intervenous iodine based contrast agents are administered in CT to:

o Enhance density differences between lesions surrounding the parenchyma.

o To demonstrate vascular anatomy and vessel patency.

PRINCIPLES OF CT INTERPRETATION

Images are oriented so that the observer is looking at the patient below.

Patient’s right side is oriented on the left side of the image.

Optimal bone detail is viewed at bone windows

Lungs are viewed at lung windows

Window width of 2,000 H, window level of 400-600H

Soft tissues

Window width of 400 -500 H, window level of 20-40H.

MAGNETIC RESONANCE IMAGING (MRI)

Produces images by means of magnetic fields and radio waves

Analyzes multiple tissue characteristics :

Hydrogen

T1 and T2 relaxation times of tissue

Blood flow within tissue

Provides the best tissue contrast.

Most tissues can be differentiated by differences in their T1 and T2 relaxation times.

Blood flow has a complex effect on MR signal that may decrease or increase signal intensity

within blood vessel.

Because the MR signal is very weak, prolonged imaging time is often required for optimal

changes.

ADVANTAGES OF MRI DISADVANTAGES OF MRI

Outstanding soft tissue contrast resolution Limited in its ability to demonstrate dense bone detail or calcifications

Provides images in any anatomic plate Involves long imaging of many pulse sequences

Absence of ionizing radiation Possesses limited spatial resolution compared with CT

CONTRAST ADMINISTRATION IN MRI:

Gadolinium chelates

- A heavy metal ion with paramagnetic effect that shortens T1 and T2 relaxation times of

hydrogen nuclei within its local magnetic field.

- Essential in providing high quality MR angiographic studies by enhancing the signal

differences between blood vessel and surrounding tissues.

- If very high tissue concentrations, such as the renal collecting system, T2 shortening

causes a significantly loss of signal intensity best seen on T2WIs.

SAFTETY CONSIDERATIONS:

MR is contraindicated in patients who have electrically, magnetically or mechanically activated

implants.

Cardiac pacemakers, insulin pumps, cochlear implants, neurostimulators, bone-

growth stimulators, and implantable drug infusion pumps.

Intracardiac pacing wires or Swan-Ganz catheters

Ferromagnetic implants such as cerebral aneurysm clips, vascular clips, and skin

staples.

Bullets, shrapnel, and metallic fragments may move and cause additional injury

or become projectiles in the magnetic field.

Metal workers and patients with heinous story of penetrating eye injuries

should be screened with radiographs of the orbit to detect intraocular metallic

foreign bodies that may dislodge, tear the retina and cause blindness.

SAFE FOR MRI

No ferromagnetic vascular clips and staples and orthopedic devices.

Prosthetic heart valves with metal components and stainless steel greenfield

filters

Pregnant patients can be scanned, provided the study is medically indicated.

Principles of Interpretation:

Soft tissue contrast is obtained through imaging sequences that accentuate differences in T1

and T2 tissue relaxation times.

Water is the major source of the MR signal in tissues other than fat.

Mineral rich structures, such as bone and calculi, and collagenous tissue such as ligaments,

tendons, fibrocartilage and tissue fibrosis are low in water contents and lack mobile protons to

produce an MR signal.

Low in signal intensity on all MR sequence

Free Water

Long T1 (low signal) and long T2 (high signal)

Found mainly as extracellular fluid, also as intracellular free water

Organs with extracellular fluid (free water)

Kidneys (Urine); ovaries and thyroid (fluid-filled follicles); spleen and penis (stagnant

blood); and prostate, testes and seminal vesicles (fluid and tubules)

Edema (increase in extracellular fluid) - prolongs T1 and T2 relaxation times.

Most neoplastic tissues have increase in extracellular fluid as well as an increase in the

proportion of intracellular free water – bright signal intensity on T2WIs.

Proteinaceous fluids

Addition of protein and free water shortens T1 relaxation time – bright.

T2 relaxation is also shortened, but the T1 shortening effect is dominant even on T2WIs-

remain bright on T2WIs.

Synovial fluid, complicated cysts, abscesses, many pathologic fluid collections, and

necrotic areas within tumors.

Soft tissues

Soft tissues that have a predominance of intracellular bound water have shorter t1 and

t2 times than do tissues with large amounts of extracellular water.

Include the liver, pancreas, adrenal glands and muscle- intermediate signal

intensities on both t1wis and t2wis

Intracellular protein synthesis shortens t1 more.

Muscle (less active protein synthesis) is lower in signal intensity on t1wis

than are organs with more active protein synthesis

Benign tumors with a predominance of normal cells, such as focal nodular

hyperplasia in the liver, tend to remain isointense with their surrounding normal

parenchyma on all imaging sequences.

Hyaline cartilage has a predominance of extracellular water but extensively

bound to mucopolysaccharide matrix

Signal resembles cellular soft tissues – intermediate on most imaging

sequences.

Fat

Protons in fat are bound to hydrophobic intermediate sized molecules and exchange

energy efficiently within their chemical environment.

T1 relaxation time is short – resulting in a bright signal.

T2 is shorter than t2 of water – lower signal intensity for fat, relative to water.

On images with lesser degrees of t2 weighting, t1 effect predominates and fat

appears isointense or slightly hyper intense compared with water.

Specialized fat – saturation imaging sequences may be used to reduce the signal

intensity of fat and enhance the visibility of edema and pathologic processes within

fat.

STIR sequences suppress signals from all tissues with short t1 times, including fat.

Flowing blood

The MR signal of slow moving blood, such as in the spleen, venous plexuses and cavernous

hemangiomas is dominated by the large amount of extracellular water present.

Low signal on t1WIs and high signal on t2WIs

Ultrasonography

Utilizes pulse echo technique

Transducer converts electrical energy to a brief pulse of high frequency sound energy

transmitted into patient- transducer becomes a received detecting echoes of sound energy

reflected from tissue – composite image is produced.

Produces nearly real time images of moving patient tissue.

Enables assessment of respiratory and cardiac movement vascular pulsations, peristalsis

and moving fetus.

Images may be produced in any anatomic plane by adjusting the orientation and angulation of

the transducer and the position of the patient.

Standard orthogonal planes: axial, sagittal and coronal.

Visualization of structures by US is limited by bone and gas contaminating structures (e.g. bowel

and lung)

Sound energy is nearly completely absorbed at interfaces between soft tissue and bone

causing an acoustic shadow limiting visualization of structures deep to the bone surface.

Soft tissue gas interfaces cause nearly complete reflection of the sound beam,

preventing visualization of deeper structures.

Doppler US:

Adjunct to real time gray scale imaging.

Detects reflection of the sound wave from a moving object RBC in flowing blood.

Can detect presence of blood flow and its direction and velocity.

Color Doppler

Gray scale + color coded Doppler information in a single image.

Stationary tissue – shades of gray.

Blood flow and moving tissue – colored.

Blood flow relatively toward the transducer face – shades of red.

Blood flow relatively away from the transducer face – shades of blue.

Lighter shades of color imply higher glow velocities

US Artifacts

Must be recognized to avoid diagnostic errors.

Acoustic shadowing

Produced by nearly complete absorption or reflection of the beam, obscuring deeper

tissue structures.

Produced by gallstones, urinary tract stones, bone, metallic objects, and gas bubbles.

Acoustic enhancement

Increased intensity of echoes deep to structures that transmit sound exceptionally well.

Such as cysts, fluid filled bladder and gallbladder.

Presence of acoustic enhancement aids in the identification of cystic masses.

Comet tall artifact is seen as pattern of tapering bright echoes trailing from small bright

reflectors

Such as air bubbles and cholesterol crystals.

PRINCIPLES OF ULTRASOUND INTERPRETATION

Fluid containing structures (cysts, dilated calyces and ureters, bladder and gallbladder

Well defined walls, absence of internal echoes, and distal acoustic enhancement

Solid tissue

Speckled pattern of tissue texture and definable blood vessels.

Fat: usually highly echogenic.

Solid organs (liver, pancreas, and kidney): lower degrees of echogenic.

Terminologies

Hypo echoic: lesions of lower echogenicity than surrounding parenchyma

Hyperopic: lesions of greater echogenicity than surrounding parenchyma

Anechoic: complete absence of echoes

E.g. simple cysts

RADIOGRAPH ULTRASOUND CT SCAN MRI

TERMINOLOGY DENSITY Radiolucent –

black Radio

opaque/radio dense – white

ECHOLGENICITY Anechoic – black

Hypoechoic – darker than parenchyma

Hyperechoic – whiter than parenchyma

Isoechoic – same as parenchyma

DENSITY Hypodense –

darker Hyperdense –

whiter Isodense –

same as parenchyma

INTENSITY Hypointense – darker Hyperintense – whiter Isointense – same as

parenchyma

AIR radiolucent Not visualized Black T1 T2

FAT Moderately radiolucent

Hyperecholic Hypodense Hypointense Hyperintense

WATER/FLUIDS Moderately radio opaque

Anechoic hyperdense Hypointense Lower intensity

than water

SOFT TISSUE Moderately radiopaque

Varying echogenicity Varying hyperdenseity

hypointense hyperintense

BONE/METAL Very radio opaque

Not visualized Very hyperdense

Intermediate intensity

Intermediate intensity

Hypointense Hypointense

PULMONARY RADIOLOGY

IMAGING MODALITIES:

Conventional Chest Radiography:

Posteroanterior (PA) and lateral chest radiographs are the mainstays of thoracic imaging

Initial imaging study in all patients with thoracic disease.

Proper radiographic technique on frontal radiographs involves assessment of four basic

features:

Penetration – faint visualization of the intevertebal disc spaces of the thoracic spine:

discrete branching vessels can be identified through the cardiac shadow and the

diaphragms.

Rotation – note the relationship between the medial cortical margins of the clavicular

heads and the spinous processes of the thoracic vertebrae.

Inspiration – apex of the right hemidiaphragm is visible below the tenth posterior rib.

Motion – cardiac margin, diaphragm and pulmonary vessels should be sharply

marginated in a completely still patient.

Portable Radiograph:

Obtained when patients cannot be safely mobilized.

There is magnification of intra thoracic structures.

Normal gravitational effect evens out the blood flow between upper and lower zones in supine

patients.

Widened upper mediastinum.

Special techniques:

Lateral decubitus

Used to detect small effusions and characterize free-flowing effusions on the decubitus

side, or to detect a small pneumothorax on the contralateral side.

Expiratory radiograph

Detection of a small pneumothorax.

Apical lordotic view

Improves visualization of the lung apices

Chest fluoroscopy

Assess chest dynamics on patients with suspected diaphragmatic paralysis.

CT and HRCT

Long windows: window width of 1000 to 2000 H and window levels of about 500 to 600 H

Routine settings for CT display of mediastinal structures are WW = 400 and WL = 40 and for the

lungs are WW = 1500 and WL = 700

Advantages of CT scan:

Superior contrast resolution

Cross-sectional display format

Indication for thoracic CT

Indication example

Evaluation of an abnormality identified on conventional radiographs

Staging of lung cancer Assessment of extent of the primary tumor and the relationship of the tumor to the pleura, chest wall

Detection of occult pulmonary metastases Extrathoracic

Detection of mediastinal nodes Lymphoma metastases infections

Distinction of empyema from lung abscess Contrast-enhanced CT can usually distinguish a peripheral lung abscess from loculated empyema

HRCT technique involves incremental thinly collimated scans (1.0 to 1.5mm) obtained at evenly

spaced intervals through the thorax for the evaluation of diffuse bronchial or parenchymal lung

disease.

Image acquisition time is limited to minimize the effects of respiratory and cardiac motion.

MRI

Morphologic studies usually require only spin echo T1W and T2W sequences in the axial plane.

Advantages of MRI:

Superior contrast resolution between tumor and fat

Ability to characterize tissues based on T1 and T2 relaxation times

Ability to scan in direct sagittal and coronal planes

Lack of need for intravenous iodinated contrast

Disadvantages of MRI

Limited spatial resolution

Detection of central pulmonary embolism Anglo-CT with high inje

Detection and evaluation of aortic disease: aneurysm, dissection, intramural hematoma, aortitis, trauma

Detection and localization of extent, including aortic branch involvement

Indication of Thoracic HRCT

Indications Examples

Solitary pulmonary nodule Breath-hold volumetric exam with thin collimation for accurate density determination without respiratory misregistration

Detection of lung disease in a patient with pulmonary symptoms or abnormal pulmonary function studies and a normal or equivocal chest film

Emphysema Extrinsic allergic alveolitis Small airways disease Immunocompromised patient

Evaluation of diffusely abnormal chest film

A baseline for evaluation of patients with chronic diffuse infiltrative lung disease for follow-up changes with therapy

Cystic fibrosis Sarcoidosis Interstitial lung disease Histiocytosis x Adult respiratory distress syndrome

To determine approach (type and location) of biopsy

Bronchoscopy versus VATS or needle biopsy

Inability to detect calcium

Difficulties in imaging the pulmonary parenchyma

More time-consuming and expensive than CT

Indications for MR of the Thorax

Evaluation of aortic disease in stable patients: dissection, ancurysm, intramural hematoma, aortitis Assessment of superior sulcus tumors Evaluation of mediastinal, vascular and chest wall invasion of lung cancer Staging of lung cancer patients unable to receive intravenous iodinated contrast Evaluation of posterior mediastinal masses

Ultrasound

Used for the detection, characterization and sampling of pleural, peripheral parenchymal and

mediastinal lesions

Can also confirm phrenic nerve paralysis without the use of ionizing radiation

Detects subpulmonic and subphrenic fluid collections

NORMAL LUNG ANATOMY

Tracheobronchial Tree

Trachea

Hollow cylinder composed of a series of c-shaped cartilaginous rings

Seen as a vertically oriented cylindric lucency extending from the cricoid cartilage

superiorly to the main bronchi inferiorly on chest radiographs.

Bronchial system

Exhibits a branching pattern of asymmetric dichotomy

Main bronchi arise from the trachea at the carina

Right bronchus forms a more obtuse angle with the long axis of the trachea and is

considerably shorter than the left main bronchus

Bronchi on the end can be seen as a ring shadow on the chest radiographs

Tracheal and main, lobar and segmental bronchial anatomy are easily seen on CT

Pulmonary arteries

Arises from the right ventricle

Left pulmonary artery is a direct continuation of the main pulmonary artery

Right artery divides into the truncus anterior and interlobar arteries

Bronchial arteries

Primary nutrient vessels of the lung

Usually arise from the proximal descending thoracic aorta at the level of the carina

Pulmonary veins

Arise within the interlobular septa from the alveolar and visceral pleural capillaries

Lobar and segmental anatomy

Interlobar fissures

Invaginations of the visceral pleura

Completely or incompletely separate the lobes from one another

There are two interlobar fissures on the right and one on the left

Right minor fissure – separates the middle from the upper lobe

Projects as a thin undulating line on frontal radiographs and as a thin

curvilinear line with a convex superior margin on lateral radiograph

Right and left major fissure – separates the lower lobe from the upper lobe

superiorly and from the middle lobe inferiorly

Not usually visualized on frontal radiographs because of the oblique

course relative to the x-ray beam

The upper lobe bronchus and its artery arising from the truncus anterior branch into three

segmental branches: anterior apical and posterior.

The middle lobe bronchus arises from the intermediate bronchus and divides into medial and

lateral segment branches, with its blood supplied by a branch of the right interlobar pulmonary

artery.

The lower lobe (RLL) is supplied by the RLL bronchus and pulmonary artery. It is subdivided into

a superior segment and four basal segments: anterior, lateral, posterior and medial.

Left upper lobe is subdivided into four segments: anterior, apicoposterior, and the superior and

inferior lingular segments.

The superior and inferior lingular arteries are proximal branches of the left inter-lobar

pulmonary artery analogous to the middle lobe’s blood supply.

Arterial supply to the anterior and apicoposterior segments parallels the bronchi and is via

branches of the upper division of the left main pulmonary artery.

The left lower lobe has a superior segment and three basal segments: anteromedial, lateral and

posterior.

Pulmonary lymphatics

Visceral pleural lymphtics

Reside in the vascular layer of the visceral pleura

Form a network over the surface of the lung that roughly parallels the margins of the

secondary pulmonary lobules

Penetrate the lung to course centrally within interlobular septa, along with the

pulmonary veins toward the hilum

Parenchymal lymphatics

Originate in proximity to the alveolar septa (juxta-alveolar lymphatics)

Course centrally with the Broncho arterial bundle

Perivenous and bronchoarterial lymphatics

Communicate via obliquely oriented lymphatics located within the central regions of the

lung.

The perivenous lymphatics and their surrounding connective tissue when distended by

fluid account for the radiographic appearance of kerley a lines.

Pulmonary interstitium

Provides support for the airways and pulmonary vessels

Begins within the hilium and extends peripherally to the visceral pleura

Axial interstitium

Extends from the mediastinum and envelopes the bronchovascular bundles

edema within is recognized radio graphically as per bronchial cuffing.

Centrilobular interstitium

These are axial fiber system continues distally along with the arterioles, capillaries, and

bronchioles to provide support for the air exchanging portions of the lung.

Peripheral interstitium

Where the pulmonary veins and lymphatics lie within

subpleural interstitium (and interlobular septa)

Parts of the peripheral inerstitium which divides secondary pulmonary lobules

Radio graphically, edema of the peripheral and supleural interstitium accounts for kerley

b lines (or interlobular lines on HRCT) and thickened fissures on chest radiographs.

Intralobular interstitium

Bridges the gap between the centrilobular and peripheral compartments.

Pathologic involvement may account for some cases of so called ground glass opacity on

chest radiographs and HRCT scans.

Respiratory bronchioles contain a few alveoli along their walls and give rise to the gas-

exchanging units of the lung:

Alveolar ducts

Alveolar sacs

Type 1 pneumocyte

Flattened squamous cells

Incapable of mitosis or repair

Type2 pneumocyte

Cuboidal cells

Course of new type 1 pneumocytes and provide a mechanism for repair

following alveolar damage

Source of alveolar surfactant

Posterioranterior chest radiograph

Soft tissues

Consist of the skin, subcutaneous fat and muscles

Visualization of normal fat in the supraclavicular fossae and the companion shadows of

skin and subcutaneous fat paralleling the clavicles helps exclude mass, adenopathy or

edema in his region.

The inferolateral edge of the pectoralis major muscle is normally seen curving towards

the axilla

Breast shadows should be evaluated routinely to detect evidence of prior mastectomy

or distorting mass.

Bones

Thoracic spine, ribs and costal cartilages, clavicles, and scapulae are routinely visible on

frontal chest radiographs.

The bodies of the thoracic vertebrae should be vertically aligned, with endplates,

pedicles, and spinous processes visualized.

Coastal cartilage calcification is seen in a majority of adults, increase in prevalence with

advancing age. Men typically show calcification at the upper and lower margins (vaginal

sign). While the majority of women develop central cartilaginous calcification (penile

sign).

Lungs

Opacity of the lungs as visualized radiographically is attributable solely to th4 presence

of the pulmonary vasculature and enveloping interstitial structures.

Arteries are solid cylinders branching along the airways and both gradually diminish in

caliber as they divide.

Pulmonary veins can often be traced horizontally to the left atrium, whereas the arteries

caqn be followed to their hilar origin, which lies more cephalad than the left atrium.

The effects of gravity explain the basal predominance of vasculature in an upright

patient, as well as isodistribution of vessels in the supine patient.

Lung mediastinal interfaces

Superior vena cava

Straight or slightly concave interface with the right upper lobe extending from

the level of the clavicle to the superior margin of the right atrium.

Lateral margin of the right atrium

Projects just to the lateral margin of the thoracic spine on a normal PA

radiograph.

Smooth convex inter with the medial segment of the middle lobe.

Pectus excavatum- displaces the cardiac shadow leftward and may not

demonstrate this interface.

Right lateral border of the inferior vena cava

Concave lateral interface at the level of the right hemidiaphragm

Best visualized on lateral radiographs

Aortic knob

Small convex indentation on the left lung

Aortopulmonary window

Inferior to the aortic arch

Usually straight or concave toward the lung.

Left lateral border of the main pulmonary artery

Inferior to the aortopulmonary window

This structure may be convex, straight, or concave toward the lung.

Enlargement is seen in diopathic condition in young women, poststenotic

dilatation in valvular pulmonic stenosis, conditions where there is increased

flow or pressure in the pulmonary arterial system.

Left atrial appendage

Forms a concave interface immediately below the main pulmonary artery.

Lateral border of the left ventricle

Comprises most of the left heart border as a gentle convex margin with the

lingua.

Diaphragm

Major inspiratory muscle comprised of muscular origins along the costal margins and

insertions into the membranousdome

Right hemidiaphragm

Overlies the liver

Apex typically lies at the level of the sixth anterior rib on frontal radiographs

exposed in deep inspiration, approximately one half interspace above the apex

of the left hemidiaphragm.

Left hemidiaphragm

Overlies the stomach and spleen

Lateral chest radiograph

Summation of the right hemi thorax over the left.

Knowledge of normal lateral radiographic anatomy can greatly aid in detection and localization

of parenchymal and cardiomediastinal processes.

Parenchymal lung disease:

Pulmonary opacity – abnormal increase in lung density

Pulmonary lucency – abnormal decrease in lung density

Pulmonary opacity

Airspace disease:

Develop when air normally present within the terminal spaces are replaced by material of soft

tissue density such as blood transudate, exudates or neoplastic cells.

Radiographic characteristics of airspace disease:

Lobar or segmental distribution

Poorly marginated

Airspace nodules

Tendency to coalesce

Bat’s wing or butterfly distribution

Rapidly changing over time

CT findings of airspace disease:

Lobar or segmental distribution

Poorly marginated that tend to coalesce

Airspace nodules

Air bronchogram

Differential diagnosis:

Pneumonia

Pulmonary edema

Hemorrhage

Neoplasm

Alveolar proteinosis

Interstitial disease:

Produced by processes that thicken the interstitial compartments of the lung with water bleed

tumor, cells, fibrous tissue or any combination of these

Patterns of interstitial disease are divided into:

Reticular network of curvilinear opacities

Fine reticular or ground glass pattern

1 to 2 mm of intervening lucent spaces

Seen in interstitial pulmonary edema and interstitial pneumonitis

Medium reticulation or honeycombing

3 to 10 mm

Seen in pulmonary interstitial fibrosis

Coarse reticular pattern

<1 cm

Seen langerhanscell histiocytosis of the lung, sarcoidosis and idiopathic

pulmonary fibrosis.

Reticulonodular

May be produced by overlap of reticular shadows or presence of both

nodular and reticular opacities.

Silicosis, sarcoldosis and lymphangitic carcinomatosis give rise to true

reticulonodular pattern.

Nodular – homogenous, well defined, small rounded lesions within the

pulmonary interstitium.

Military < 2 mm

Micro nodules – 2 to 7 mm

Nodules – 7 to 30 mm

Masses – 30 mm

Military or mironodular pattern are seen in granulomatous processes

(military or histoplasmosis) hematogenous pulmonary metastasis

(thyroid and renal cell

And pneumoconiosis (silicosis)

Nodules and masses are seen in metastatic disease to the lung

Linear – processes that thickens the axial (Broncho vascular) or peripheral

interstitium of the lung. Produce parallel linear opacities radiating from the hila

when visualized in length or peribronchial cuffing when visualized end on.

Kerley A lines - < 1 mm thick lines obliquely oriented and course through

the lung toward the hila 2 to 6 cm long.

Corresponds connective tissue within the lung

Kerley B lines – peripheral lines that course perpendicular to and

contact the pleural space 1 to 2 cm long.

Represent thickened peripheral subpleural interlobular septa.

Atelectasis:

Incomplete expansion of the lungs

4 mechanisms of atelectasis:

Obstructive/resorptive atelectasis

Most common form

Secondary to complete endobronchial obstruction of lobar bronchus with

resorption of gas distally

Common causes are bronchogenic carcinoma foreign bodies’ mucous plugs and

malpositioned endotracheal tube.

Passive/relaxation atelectasis

Result from mass effect of an air or fluid collection within the pleural space on

the adjacent lung.

Causes are pneumothorax and pleural effusion.

Compressive atelectasis

Form of passive atelectasis in which intrapulmonary mass compresses adjacent

lung parenchyma.

Causes include bullae, abscess and tumors.

Cicatricial atelectasis

Produced by processes resulting in parenchymal fibrosis and reduce alveolar

volume.

Most often seen in chronic upper lobe fibrotic tuberculosis.

Adhesive atelectasis

Occurs in association with surfactant deficiency disease.

Radiograph show diminution in lung volume.

Pulmonary lucency

Abnormal lucency of the lung may be localized or diffuse

Diffuse lung lucency

Unilateral hyperlucency

Result in decrease in blood flow to the lung.

Hypoplasia of the right or left pulmonary artery.

Lobar resection or atelectasis

Pulmonary arterial obstruction

Swyer james syndrome

Emphysema most common with severe disease

Bilateral hyperlucent lung:

May be simulated by an over penetrated film or by a thin patient

Result of diminished pulmonary blood flow

Congenital pulmonary stenosis

Pulmonary emphysema

Asthma

Focal radiolucent lesions

Includes cavities, cysts, bullae, blebs and pneumatoceles

Cavities

Form when a pulmonary mass undergoes necrosis and communicates

with an airway

The wall of a cavity is usually irregular or lobulated

Wall is greater than 1 mm thick

Lung abscess and necrotic neoplasm are the most common cavitary

pulmonary lesions

Bulla

Gas collection within the pulmonary parenchyma

>1 cm in diameter and has a thin wall <1 mm thick

Represents a focal area of parenchymal destruction (emphysema) and

may contain fibrous strands, residual blood vessels or alveolar septa

Air cyst

Well-circumscribed intrapulmonary gas collection

Smooth thin wall >1 mm thick

Bleb

Collection of gas <1 cm in size within the lawyers of the visceral pleura

Usually found in the apical portion

Not seen on plain radiographs but may be visualized on chest CT

Rupture can lead to spontaneous pneumothorax

Pneumatoceles

Thin-walled, gas-containing structures

Represent distended airspaces distal to a check-value obstruction of a

bronchus or bronchiole

Most commonly secondary to staphylococcal pneumonia

Pneumonia:

Microorganisms enter the lung via three potential routes:

Tracheobronchial tree

Pulmonary vasculature

Direct spread from infection in the mediastinum, chest wall or upper abdomen.

1. Lobar pneumonia:

Typical of pneumococcal pulmonary infection.

The inflammatory exudate begins within the distal airspaces.

Airways are usually spared, air bronchograms are common and significant volume loss is

unusual.

2. Bronchopneumonia:

Most common patterns

Most typical staphylococcal pneumonia

Early stages of inflammation is centered primarily in and around lobular bronchi

As the inflammation progresses, exudative fluid extends peripherally along the bronchus to

involve the entire pulmonary lobule.

Radio graphically, multifocal opacities that are roughly lobular in configuration produce a

patchwork quilt appearance.

Exudate within the bronchi accounts for the absence of air bronchograms in bronchopneumonia

3. Interstitial pneumonia

Seen in viral and mycoplasma infection

There is inflammatory thickening of bronchial and bronchiolar walls and the pulmonary

interstitium

Radiographic findings – pattern of airways thickening and reticulonodular opacities

Segmental and sub segmental atelectasis from small airways obstruction is common.

Pulmonary tuberculosis:

Mycobacterium tuberculosis is an aerobic acid fast bacillus

Two principal forms of tuberculous pulmonary disease are recognized clinically and

radiographically

Primary tuberculosis (TB)

Reactivation or post-primary disease

Involves cell-mediated immunity (delayed hypersensitivity)

Primary PTB:

Has classically been a disease of childhood

Ranke complex: calcified parenchymal focus (the ghon lesion) and nodal calcification.

Nonspecific focal pneumonitis – seen as small ill-defined areas of segmental or lobar

opacification.

Unllateral/ollateral hilar or mediastinal lymph node enlargement.

Post-primary PTB:

Tends to occur in the apical and posterior segments of the upper lobes and the superior

segments of the lower lobes as ill-defined patchy and nodular opacities.

Cavitation: may lead to transbronchial spread of organisms and result in a multifocal

bronchopneumonia.

Rasmussen aneurysm – erosion of a cavitary focus into a branch of the pulmonary artery can

produce an aneurysm and cause hemoptysis.

Parenchymal healing is associated with fibrosis, bronchiectasis and volume loss (cicatrizing

atelectasis) in the upper lobes.

Military TB:

May complicate either primary or reactivation disease.

Results from hematogenous dissemination of tubercle bacilli and produces diffuse

bilateral 2 to 3 mm pulmonary nodules.

Asthma:

An airway disorder characterized by the rapid onset of bronchial narrowing with

spontaneous resolution or improvement as a result of therapy.

Radiographic findings include:

Hyperinflation

Bronchial wall inflammation and thickening (peribronchial cuffing and tram tracking)

In some patients the hila are prominent from transient pulmonary arterial hypertension.

Emphysema:

Defined as an abnormal permanent enlargement of the airspaces distal to the terminal

bronchioles accompanied by destruction of alveolar walls and without obvious fibrosis.

Frontal and lateral chest radiographs are the initial radiographic examinations obtained in

patients with suspected emphysema.

Hyperinflation – most important plain radiographic finding.

1. Centrilobular emphysema

Most common affects the upper lobes to a greater extent than the lower lobes

Airspaces distention in the central portion of the lobule sparing of the more distal portions of

the lobule.

2. Panlobular emphysema

Affects lower lobes more than the upper lobes.

Uniform distention of the airspaces throughout the substance of the lobule from the central

respiratory bronchioles to the peripheral alveolar sacs and alveoli.

3. Paraseptal emphysema

Most often seen in the immediate subpleural regions of the upper lobes.

Selective distention of peripheral airspaces adjacent to the interlobular septa with sparing of the

centrilobular region.

May coalesce to form apical bullae.

4. Paracicatricial or irregular emphysema

Destruction of lung tissue associated with fibrosis; has no consistent relationship to a given

portion of the lobule.

Often seen in association with old granulomatous inflammation.

Bronchogenic carcinoma:

Majority of patients are cigarette smokers who are over 40 yrs of age.

Men are more affected.

Solitary pulmonary nodule or mass and a hilar mass with or without bronchial obstructionare

the most common radiographic findings.

Obstruction of the bronchial lumen can result into resorptive atelectasis or obstructive

pneumonitis

Pancoast tumor (superior sulcus) – peripheral neoplasm arising in the lung apex indented

superior by the subclavian artery.

Majority are squamous cell carcinomas or adenocaricinomas.

Apical thickness of >5 mm asymmetry of the apical opacities of >5 mm or evidence of rib

destruction should prompt further evaluation with helical CT or MR.

Subtypes of bronchogenic carcinoma:

adenocarcinoma

Most common type of lung cancer (35% of bronchogenic carcinoma)

Usually located in the lung periphery; ¼ of cases found in central portions.

Arise from the bronchiolar or alveolar epithelium.

They have irregular or speculated appearance where they invade adjacent lung

5 year survival rate of 17%

Squamous cell carcinoma

2nd most common subtype of bronchogenic carcinoma (25%)

Arises centrally within a lobar or segmental bronchus.

Usually present as hilar mass with or without obstructive pneumonitis or atelectasis

5 year survival rate 15%

Small cell carcinoma

25% of bronchogenic carcinomas and arise centrally within the main or lobar bronchi.

Most malignant neoplasm arising from neuroendocrine (kultchitsky) cells.

Produces a hilar or mediastinal mass with extrinsic bronchial compression.

5 year survival rate 5%

Large cell carcinoma

15% of bronchogenic carcinomas

Present as a large peripheral mass usually peripherally located

5 year survival rate of 11%

TMN classification of lung cancer

Primary tumor (T)

Tx Malignant cells in sputum without identifiable tumor.

T0 No evidence of primary tumor.

T1 Tumor <3.0 cm in diameter surrounded by lung or visceral pleura arising distal to a main bronchus.

T2 Tumor >3.0 cm in diameter any tumor invading the visceral pleura any tumor with atelectasis or obstructive pneumonitis of less than an entire

lung; tumor must be >2 cm from the tracheal carina.

T3 Any tumor with localized chest wall diaphragmatic mediastinal pleural or pericardial invasion the tumor may be, 2 cm from the carina but cannot involve the carina.

T4 Any tumor that invades the mediastinum or vital mediastinal structures including the heart, great vessels trachea carina or vertebral body; separate tumor nodules in the same lobe; presence of a malignant pleural effusion.

Nodal metastases (N)

N0 No evidence of nodal metastases

N1 Metastasis to ipsilateral peribronchial or hilar nodes including involvement by contiguous spread of tumor.

N2 Metastasis to ipsilateral mediastinal or subcarinal nodes.

N3 Metastasis to contralateral mediastinal or hilar nodes or scalene or supraclavicular nodes.

Distant metastases (M)

M0 No evidence of distant metastases.

M1 Distant metastases separate tumor nodules in different lobes.

Clinical staging of lung cancer based on TNM classification

Ia – T1 N0 M0

Ib – T2 N0 M0

IIa – T1 N1 M0

IIb – T2 N1 M0

T3 N0 M0

IIIa – T1 or T2 N2 M0

T3 N1 or N2 M0

IIIb – any T N3 M0

T4 Any N M0

IV – any T any N M1

Pulmonary vascular disease:

Pulmonary venous hypertension

Elevation in pulmonary venous pressure

Causes: obstruction to left ventricular inflow left ventricular systolic dysfunction mitral valve

regurgitation.

Radiographic findings include: enlargement of pulmonary veins and redistribution of pulmonary

blood flow to nondependent lung zones.

Pulmonary arterial hypertension:

Defined as systolic pressure in the pulmonary artery of 30 mm Hg

Causes: increase resistance to pulmonary blood flow (emphysema, chronic hypoventilation

cystic lung disease constrictive bronchiolitis cystic fibrosis)

Typical radiographic findings are enlarged main and hilar pulmonary arteries that taper rapidly

toward the lung periphery.

There may be associated right ventricular enlargement.

Enlarged pulmonary artery – a transverse diameter of the proximal interlobar pulmonary artery

on PA chest radiograph exceeding 16 mm

Pulmonary edema:

The interstitial spaces of the lungs are kept dry by pulmonary lymphatic located within the

axialand peripheral interstitium of the lung.

There are no lymphatic structures immediately within the alveolar walls, alveolar interstitial

fluid is drawn to the lymphatics by pressure gradient.

When the rate of fluid accumulation exceeds the lymphatic drainage capabilities of the lungs

fluid accumulate first within the interstitial space

Progressive fluid accumulation eventually produces flooding of the alveolar spaces.

Hydrostatic pulmonary edema – most common cause.

Interstitial edema:

Radiologic appearance of results from thickening of the components of the interstitial spaces by

fluid.

Peribronchial cuffing and tram tracking thickening of the peribronchovascular interstitium.

Loss of definition of the intrapulmonary vascular shadows – thickening of the axial interstitium.

Kerley lines.

Airspace edema:

Occurs when fluid from the interstitum spills into the alveoli

Upright radiograph show bilateral symmetrical airspace opacities predominantly in the mid to

lower lobes.

Pleura:

The pleura is a serous membrane subdivided into:

Visceral pleura – covers the lungs and forms the interlobar fissure.

Parietal pleura – lines the mediastinum diaphragm and thoracic cage

The potential space between the visceral and parietal pleura is the pleural space which contains

2 to 5 ml of fluid which serves as a lubricant during breathing.

Under normal conditions, pleural fluid is formed by filtration form systemic capillaries in the

parietal pleura and resorbed via the parietal pleural lymphatics.

Pleural effusion:

Occurs when there is imbalance between the formation and resorption of pleural fluid.

Pleural effusions may be classified by:

Gross appearance (bloody, chylous, purulent, serous)

Causative disease

Pathophysiology of abnormal pleural fluid formation (transudative versus exudative)

The radiographic appearance of pleural effusions depends upon:

Amount of fluid present

Patient’s position during the radiographic examination

Presence or absence of adhesions between the visceral and parietal pleura

Small amounts of pleural fluid initially collect between the lower lobe and diaphragm in a

subpulmonic location – as more fluid accumulates, it spills into the posterior and lateral

costophrenic sulci.

On upright PA chest radiographs

Moderate amount of pleural fluid (>175 ml) in the erect patient will have homogeneous

lower zone opacity.

The lateral costopherenic sulcus will show a concave interface towards the lung

(meniscus sign)

Pleural fluid may extend into the interlobar fissures

Free fluid within the minor fissure is usually seen as smooth, symmetric thickening on a

frontal radiograph.

In patients with suspected pleural effusion, a lateral decubitus film with the affected side down

is the sensitive technique to detect small amounts of fluid.

There will be fluid shifting to the dependent portion of the thorax

A large pleural effusions can cause passive atelectasis of the entire lung producing an opaque

hemithorax.

The radiographic detection of pleural effusion in the supine patient can be difficult because fluid

accumulates in a dependent location posteriorly.

The most common findings is a hazy opacification of the affected hemithorax with obscuration

of the hemidiaphragm and blunting of the lateral costophrenic angle.

On axial CT scans pleural fluid layers posteriorly with a characteristic meniscoid appearance and

has a CT attenuation value of 0 to 20 H.

MEDIASTINUM

A narrow vertically oriented structure that resides between the medial parietal pleuraol layers of the

lungs.

Contains central cardiovascular tracheobronchial structures and the esophagus enveloped in fat with

intermixed lymph nodes

Divided into superior (thoracic inlet) and inferior components with the inferior mediastinum subdivided

into anterior middle and posterior compartments.

A line drawn through the sternal angel anteriorly and fourth thoracic intervertebral space posteriorly

divides the mediastinum into superior and inferior compartments.

Contents of the thoracic inlet and mediastinum

compartments contents

Thoracic inlet Thymus Confluence of the right and left internal jugular and subclavian veins Right and left carotid arteries Right and left subclavian arteries Trachea Esophagus Prevertebral fascia Phrenic, vagus, recurrent laryngeal nerves muscles

Anterior mediastinum Internal mammary vessels Internal mammary and prevascular lymph nodes thymus

Middle mediastinum Heart and pericardium Ascending and transverse aorta Main and proximal right and left pulmonary arteries Confluence of pulmonary veins Superior and inferior vena cava Trachea and main bronchi Lymph nodes and fat within mediastinal spaces

Posterior mediastinum Esophagus Azygos and hemiazygos veins Thoracic duct sympathetic ganglia and intercostal nerves Lymph nodes

Mediastinal mass:

Patients with mediastinal masses tends to present in one of two fashions:

With symptoms related to local mass effect or invasion of adjacent mediastinal structures (stridor in a

patient with thyroid goiter)

Incidentally with an abnormality on a routine chest radiograph

Thoracic inlet masses

Marginated by the first rib and represents the junction between the neck and thorax

Commonly present as neck masses or with symptoms of upper airway obstruction resulting from

tracheal compression.

Thyroid masses lymphomatous nodes and lymphangiomas are the most common thoracic masses

Thoracic lnlet masses

Thyroid mass Goiter Malignancy Thyromegaly resulting from thyroiditis

Parathyroid mass Hyperplasia Adenoma carcinoma

Lymph node mass Lymphoma Hodgkin Non-Hodgkin Matastases Inflammatory tuberculosis

lymphangioma