DR. HARSHIL A. KALARIA RESIDENT,.

DEPARTMENT OF RADIOLOGY

UNDERSTANDING HRCT CHEST

TECHNICAL ASPECT OF HRCT; NORMAL LUNG ANATOMY & HRCT FINDINGS OF LUNG DISEASE

HRCT ------ MEANINGo It is often used for anything and everything to do

with “high resolution”.o Resolution : Means ability to resolve small object

that are close together ,as separate form.

Actual meaning o A scan performed using high- spatial frequency

algorithm to accentuate the contrast between tissue of widely differing densities, eg.,

- air & vessels (lung) - air & bone (temporal & paranasal sinus)

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INTRODUCTION• HRCT -- Use of thin section CT images (0.625 to 2 mm slice

thickness) often with a high-spatial-frequency reconstruction algorithm to detect and characterize disease affecting the pulmonary parenchyma and airways.

• Superior to chest radiography for detection of lung disease, points a specific diagnosis and helps in identification of reversible disease.

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HISTORY• 1982– The term HRCT was first used by TODO et. Al

• 1985 – Nakata et.al and Naidich et.al published first report on HRCT

Since then has been an important tool in pulmonary medicine

• Recent development of MDCT scanner capable of volumetric high resolution scanning has improved the investigation

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TECHNICAL ASPECTParameterso Slice thicknesso Kvpo mAso Scan timeo FoVo Interslice gap (collimation)o Filming.

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SLICE THICKNESS

• Thin sections 0.5 – 1.5 mm is essential for optimal spatial

resolution

• Thicker slices are prone for volume averaging and reduces

ability to resolve smaller structure

• Better for delineation of bronchi, wall thickness and

diameter

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Reconstruction Algorithm

• Denotes the frequency at which the acquired scan data are recorded when creating the image.

• Using a high-resolution algorithm is critical element in performing HRCT.

• High spatial frequency or sharp algorithm -- bone algorithm is used which reduces image smoothing and better depicts normal and abnormal parenchymal interface.

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Standard algorithmHigh resolution algorithm 10

Kilovolts (Peak), Milliamperes, and Scan Time

• In HRCT image, noise is more apparent than standard CT.

• Noise – 1/√ mAs X Kvp X scan time

• As increasing scan time is not feasible, mAs and Kvp are altered to reduce noise

• Noise decreases with increase in Kvp and mAs.

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• For routine technique – Kvp -- 120-140 mAs -- 200- 300

• Increased patient and chest wall thickness are associated with increase image noise, may be reduced by increasing mAs and Kvp

• Scan Time : As low as possible (1-2 sec) to minimize motion artifact.

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WINDOW SETTINGS

Lung windowWindow level setting ranging from – 600 to – 700

HU and window widths of 1000 to 1500 HU are appropriate for a routine lung window.

Soft tissue windowWindow level/width setting of 40-50/ 350-450

HU are best for evaluation of the mediastinum, hila, and pleura.

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LOW DOSE HRCT

• Low dose HRCT uses Kvp of 120- 140 and mA of 30-20 at 2 sec scan time.

• Equivalent to conventional HRCT in 97 % of cases

• Disadvantage : Fails to identify GGO in few cases and have more prominent streak artifact.

• Not recommended for initial evaluation of patients with lung disease.

• Indicated in following up patients with a known lung abnormality or in screening large populations at risk for lung dz.

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Matrix size, Field of View, and Target reconstruction• Matrix size : Largest available matrix s/b used – 512 x 512

• Field of view : smallest FOV that will encompass the patient is used as it will reduce the pixel size. (commonly 35 to 40)

• Retrospectively targeting image reconstruction to a single lung instead of the entire thorax significantly reduces the FOV and image pixel size, and thus increases spatial resolution.

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• INTERSLICE GAP – varies from examination to examination, but is usually 10- 20 mm

• INSPIRATORY LEVEL : Routine HRCT is obtained in suspended full inspiration, which

optimizes contrast between normal structures, various abnormalities and normal aerated lung parenchyma; and

reduces transient atelectasis, a finding that may mimic or obscure significant abnormalities.

• EXPIRATORY SCAN : valuable in obstructive lung disease or airway abnormality

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Patient Position and the Use of Prone Scanning

• Supine adequate in most instances.

• Prone for diagnosing subtle lung

abnormalities.

e.g., asbestosis, suspected early lung

fibrosis

• Prone scan is useful in differentiating

dependent lung atelectasis from early lung

fibrosis18

Axial CT image shows opacity in the posterior part of the lung which could represent dependent opacity or pulmonary inflammation. The prone images shows complete resolution of the opacity suggesting dependent atelectasis.

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Persistent opacity in the posterior lung in a patient with pulmonary fibrosis.

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TECHNIQUE OF SCAN ACQUISITION:1. Spaced axial scans : Obtained at 1cm intervals from lung

apices to bases. In this manner, HRCT is intended to “sample” lung anatomy

It is assumed that the findings seen at the levels scanned will be representative of what is present throughout the lungs

Results in low radiation dose as the individual scans are widely placed

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2. Volumetric HRCT -

MDCT scanner are capable of rapid scanning and thin slice acquisition.

Advantages :

1. Viewing of contagious slice for better delineation of lung abnormality

2. Complete imaging of lung and thorax

3. Reconstruction of scan data in any plane using MIPs or MinIPs.

4. diagnosis of other lung abnormalitiesDisadvantage : greater radiation dose. It delivers 3-5 times

greater radiation.22

Multidetector Helical HRCT

Multidetector CT is equipped with a multiple row detector array

Multiple images are acquired due to presence of multiple detectors

Advantages : - shorter acquisition times and retrospective creation of both thinner and thicker sections from the same raw data 

Acquisition time is so short that whole-lung HRCT can be performed in one breath-hold.

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Which is better HRCT or MD- HRCT

Various study shows the image quality of axial HRCT with multi-detector CT is equal to that with conventional single-detector CT.

HRCT performed with spaced axial images results in low radiation dose as compared with MD-HRCT.

Increased table speed may increase the volume-averaging artifact and may result in indistinctness of subtle pulmonary abnormalities. 

MDCT provides for better reconstruction in Z axis

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Radiation dosePA CHEST Radiograph ----- ----- ----- 0.05 mSvSpaced axial HRCT (10mm space) ----- 0.7 mSv ( 14 X ray)Spaced axial HRCT (20 mm space) ------ 0.35 mSv ( 7 X ray)Low Dose Spaced axial HRCT -------- 0.02 mSV MD-HRCT ---- ------- 4 - 7 msv ( 60-80 x ray)

Combining HRCT scan at 20 mm interval with low mAs scan (40 mAs) would result in radiation comparable to conventional X ray.

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Summary of HRCT protocol  Collimation: thinnest available collimation (1.0-1.5 mm).  Reconstruction algorithm: high-spatial frequency or

“sharp” algorithm (i.e., GE “bone”).  Scan time: as short as possible (1 sec or less).  kV(p), 120-140; mA, 240.  Matrix size: largest available (512 × 512).

Optional  kV(p)/mA: Increased kV(p)/mA (i.e., 140/340).

    Recommended in large patients. Otherwise optional.  Targeted reconstruction: (15- to 25-cm field of view).  Reduced mA (low-dose HRCT): 40-80 mA.

HRCT ARTIFACT• Streak ArtIfacts :

Fine, linear, or netlike opacities

Radiate from the edges of sharply

marginated , high-contrast structures

such as bronchial walls, ribs, or vertebral

bodies.

More evident on low mA

Mechanisms: beam hardening, photon

starvation, and aliasing. 27

Motion-related artIfacts

• Pulsation / Star artefacts

• Doubling artefacts.

• Stair-step artefacts in sag/coro

reconstruction.

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MODIFICATION OF SCAN PROTOCOL

Scan protocol can be modified in relation to disease or patients comfort.

If a disease has basal predominance, it may be wise to begin scanning near the diaphragm and proceed cephalic .

Caudad for disease with an upper-lobe predominance (e.g., sarcoidosis)

An alternative approach - cephalad in all patients.

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MAXIMUM INTENSITY PROJECTION maximum intensity projection (MIP) is a 

volume rendering method for 3D data that projects in the visualization plane thevoxels with maximum intensity that fall in the way of parallel rays traced from the viewpoint to the plane of projection

Volume RenderingVS Maximum Intensity Projection

(a) Volume-rendered image provides clear definition of individual vessels. (b) MIP image reconstructed from the same volume data shows all of the vessels, but their outlines merge; it is impossible to visualize the spatial relationships between the vessels or to delineate individualvessels on the MIP image.

MAXIMUM INTENSITY PROJECTION

Maximum-intensity projection (MIP) image in a patient with small lung nodules obtained using a multidetector-row spiral CT scanner with 1.25-mm detector width and a pitch of 6. A: A single HRCT image shows two small nodules (arrows) that are difficult to distinguish from vessels. B: An MIP image consisting of eight contiguous HRCT images, including A, allows the two small nodules to be easily distinguished from surrounding vessels.

first step in HRCT interpretation of diffuse lung diseases is a good quality scan

. Resolution and size or orientation of structures. The tissue plane, 1 mm thick, and the perpendicular cylinder, 0.2 mm in diameter, are visible on the HRCT scan because they extend through the thickness of the scan volume or voxel. The horizontal cylinder cannot be seen.

MDCT Techniques

Combined “routine” and HRCT studies5 mm sections q 5 mm (separate lung and

mediastinal reconstruction algorithms):1 – 1.25 mm sections q 10 mm (lung algorithm)

Optional image acquisitionsSupine and prone 1 – 1.25 mm sectionsInspiratory/expiratory 1 -1.25 mm sectionsLow dose technique (mAs 40 – 80)

Optional Reconstruction techniquesSliding maximum and minimum intensity projection

images (MIPs/ MINIPs): 5 mm’s q 5 mm

INDICATIONSDetect interstitial lung disease not seen on

chest x-rayAbnormal pulmonary function testsCharacterize lung disease seen on X-rayDetermine disease activityFind a biopsy site

INDICATIONSHemoptysis Diffusely abnormal CXRNormal CXR with abnormal PFT’s Baseline for pts with diffuse lung diseaseSolitary pulmonary nodulesReversible (active) vs. non-reversible (fibrotic)

lung disease Lung biopsy guideF/U known lung disease Assess Rx response

LUNG ANATOMYRight lung is divided by major and minor fissure into 3 lobes and 10 bronchopulmonary segments

Left lung is divided by major fissure into 2 lobes with a lingular lobe and 8 bronchopulmonary segments

ANATOMYThe trachea (windpipe) divides into left and the right mainstem bronchi, at the level of the sternal angle (carina).

The right main bronchus is wider, shorter, and more vertical than the left main bronchus.

The right main bronchus subdivides into three lobar bronchi, while the left main bronchus divides into two.

The lobar bronchi divide into tertiary bronchi, also known as segmentalinic bronchi, each of which supplies a bronchopulmonary segment.

ANATOMYThe segmental bronchi divide into

many primary bronchioles which divide into terminal bronchioles, each of which then gives rise to several respiratory bronchioles, which go on to divide into two to 11 alveolar ducts. There are five or six alveolar sacs associated with each alveolar duct. The alveolus is the basic anatomical unit of gas exchange in the lung.

TRACHEAL ANATOMY10-12 cm in lengthExtrathoracic (2-4cm) and Intrathoracic(6-9cm

beyond manubrium)In men, tracheal diameter averages 19.5 mm

and in women, tracheal diameter is slightly less, averaging 17.5 mm

The posterior portion of the tracheal wall is a thin fibromuscular membrane termed the posterior tracheal membrane

There is marked variability in the cross-sectional appearance of the trachea, which may appear convex posteriorly, flat, or convex anteriorly

The membranous posterior membrane allows esophageal expansion during expiration

Contains glands, small arteries, nerves, lymph vessels and elastic fibers

Trachealis muscle overlies esophageal muscle and epithelium

BRONCHIAL ANATOMYAirways divide by dichotomous branching, with

approximately 23 generations of branches from the trachea to the alveoli.

The wall thickness of conducting bronchi and bronchioles is approximately proportional to their diameter.

Bronchi with a wall thickness of less than 300 um is not visible on CT or HRCT.

As a consequence, normal bronchi less than 2 mm in diameter or closer than 2 cm from pleural surfaces equivalent to seventh to ninth order airways are generally below the resolution even of high-resolution CT

There are approximately 23 generation of dichotomous branchingFrom trachea to the alveolar sac

HRCT can identify upto 8th order central bronchioles

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BRONCHUSBLOOD SUPPLY Bronchial Arteries( 2 on left side i.e.

superior and inferior and 1 on right side) Left arises from thoracic aorta Right from either thoracic aorta, sup. lt. bronchial or

right 3rd intercostal artery

VENOUS DRAINAGE on right- azygous vein on left- left

superior intercostal or accessory hemiazygous vein

NERVE SUPPLY Pulmonary plexus at hilum (vagus and sympathetic)

BRONCHOARTERIAL RATIO (B/A)Internal diameter of both bronchus and

accompanying arterial diameter calculated and ratio measured.

If obliquely cut section seen, then the LEAST diameter is considered.

Normal ratio is 0.65-0.70B/A ratio more than 1.0 indicates

bronchiactasis.

BRONCHIAL WALL THICKNESS (T/D)Wall thickness proportionately decreases as

the airway divides further as according to the diameter of the airway.

T/D ratio approximates to 20% at any generation of airway.

The Nomenclature Adopted by the Ad HOC lnternational Committee Meeting at the Time of the lnternational Congress of Otorhinolaryngology in 1949 [I]"

International Nomenclature

Brock Jackson and Huber

Right upper lobe bronchusApical (RB1)Posterior (RB2)Anterior (RB3)Middle lobe bronchusLateral (RB4)Medial (RB5)Right lower lobe bronchusApical (RB6)Medial basal (cardiac) (RB7)Anterior basal (RB8)Lateral basal (RB9)Posterior basal (RB10)

PectoralSubapical

Apical

LateralMedial

ApicalCardiac

Anterior basalMiddle basal

Posterior basal

AnteriorPostenor

Apical

LateralMedial

SuperiorMedial basal

Anterior basalLateral basal

Posterior basal

The Nomenclature Adopted by the Ad HOC lnternational Committee Meeting at the Time of the lnternational Congress of Otorhinolaryngology in 1949 [I]"

International Nomenclature

Brock Jackson and Huber

Left upper lobe bronchusUpper divisionApical (LB1)Apicoposterior LB1 and LB2Posterior (LB2)Anterior (LB3)LingulaSuperior (LB4)Inferior (LB5)Left lower lobe bronchusApical (LB6)Anterior basal (LB8)Lateral basal (LB9)Posterior basal (LB10)

ApicopectoralApical

SubapicalPectoral

UpperLower

ApicalAnterior basalMiddle basal

Posterior basal

ApicalApical-posterior

PosteriorAnterior

SuperiorInferior

SuperiorAnterior medial

basalLateral basal

Posterior basal

MEDIASTINUMBroad central portion that separate the two

laterally placed pleural cavities.Imaginary plane passes through T4 divides it

into Superior & Inferior mediastinumInferior mediastinum is further divided-Heart enclosed in pericardium (M)Sternum to anterior pericardium (A)Posterior pericardium to vertebrae (P)

INTERSTITIAL ANATOMYLung is supported by a network of connective

tissue called interstitiumInterstitium not visible on normal HRCT but

visible once thickened.Interstitium is constituted by AXIAL fibre

system (peribronchovascular & centrilobular), PERIPHERAL fibre system (subpleural & interlobular septa) and SEPTAL fibre system (intralobular septa)

Secondary LobuleIt is the smallest lung unit that is surrounded

by connective tissue septa.It measures about 1-2 cm and is made up of 5-15

pulmonary acini, that contain the alveoli for gas exchange.

The secondary lobule is supplied by a small bronchiole (terminal bronchiole) in the center, that is parallelled by the centrilobular artery.

Pulmonary veins and lymphatics run in the periphery of the lobule within the interlobular septa.

SECONDARY PULMONARY LOBULE

Smallest lung unit that is surrounded by connective tissue septa (Miller)

The basic anatomic unit

Irregular polyhedral in shape.

Measures 1 to 2.5 cm60

Anatomy of the Secondary Lobule and Its Components

1. Interlobular septa and contiguous subpleural interstitium,

2. Centrilobular structures, and

3. Lobular parenchyma and acini.

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Interlobular septa and contiguous subpleural interstitium

The secondary pulmonary lobule is marginated by septa which extends from the pleural surface.

They measure 0.1 mm in thickness.They are less well defined in central lung

Lobular core :The secondary lobule is supplied by arteries and

bronchioles that measures approximately 1 mm in diameter.

It consists of functioning lung parenchyma namely the alveoli, alveolar duct and vessels. The parenchyma is supported by network of central and peripheral fibers of interstitium.

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PULMONARY ACINUS

Portion of lung parenchyma supplied by a single respiratory Bronchiole.

Size is 7 to 8 mm in adults

3 to 24 acini = Sec Pul. Lobule

Primary Lobule: Lung parenchyma associated with a single Alveolar duct.

4-5 Primary Lobules Acinus 63

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A group of terminal bronchioles

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Accompanying pulmonary

arterioles

67

Surrounded by lymph vessels

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Pulmonary veins

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Pulmonary lymphatics

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Connective Tissue Stroma

LUNG INTERSTITUM

Lung interstitium

Axiel fiber system

Peribronchovascular

interstitiu

m

Centrilobular

interstitium

Peripheral fiber sysem

Subpleural

interstitium

Interlobular septa

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The peribronchovascular interstitum invests the bronchi and pulmonary artery in the perihilar region.

The centrilobular interstitium are associated with small centrilobular bronchioles and arteries

The subpleural interstitium is located beneath the visceral pleura; envelops the lung into fibrous sac and sends connective tissue septa into lung parenchyma.

Interlobular septa constitute the septas arising from the subpleural interstitium.

LUNG INTERSTITUM

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The normal pulmonary vein branches are seen marginating pulmonary lobules. The centrilobular artery branches are visible as a rounded dot

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Anatomy of pleural surfaces and chest wall.

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Every CT scan starts with a scout view, a projection image that looks like a second rate X-ray.

A line on scout view tells you the level of axial cut.

HOUNSFIELD UNIT (HU)HU scale is a linear transformation of the original

linear attenuation coefficient measurement into one in which radio density of distilled water at STP is defined as zero HU, while radio density of air at STP is defined as -1000 HU.

Fat -50 to -100 HUBlood +30 to 45 HUBone >+400 HUMuscle +40HUContrast +130 HU

APPEARANCE ON CT SCANAIR JET BLACKFAT MODERATELY

BLACKWATER GRAYMUSCLES SLIGHT WHITEBONES WHITECALICIFICATION DENSE WHITE

LUNG WINDO

W

MEDIASTINAL WINDOW

BONE WINDOW

NORMAL LUNG ATTENUATION

Normal lung attenuation : –700 to – 900 HU

Attenuation gradient : densest at dependent region of lung as a result of regional difference in blood and gas density due to gravity

Difference in attenuation of anterior and posterior lung ranges from 50 – 100 HU

In children, lung attenuation is greater than adults.

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NORMAL EXPIRATORY HRCT

Performed to detect air trapping in small airway obstruction

Attenuation increases with expiration (ranges from 100 to 130 HU)

60 % of normal individual shows air trapping in the superior segment of lower lobe and involving single lobule, normal variant.

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LOBAR AND BRONCHIAL ANATOMY ON HRCT THORAX

RIGHT APICAL SEGMENT

LEFT APICAL SEGMENT

TRACHEA

ESOPHAGUSRB1 LB

1

CARINA

LEFT MAIN BRONCHUS

RIGHT MAIN BRONCHUS

RB2 RB1

RB3 LB3

LB1,2

BRONCHUS INTERMEDIUS

LEFT UL BRONCHUS

RIGHT ML BRONCHUS

RB5

LUL

LLL

RLL

RML

RB5 LB4

LB5

RLL BRONCHUS

LLL BRONCHUS

LB6

LINGULAR BRONCHUS

RB6

RB7LB6

RLL BRONCHUS

LLL BRONCHUS

MAJOR FISSURE

RB8

RB9

RB10

LB10

LB9

LB8

RLL

LML

LLL

RML

LB2

LB6

LB10

RB7

RB10

RB9

RB6

RB2

RB1

RB2

LB9

LB1,2

UL

LL

UL

LL

ML

RB1 joining RUL bronchus

LB1,2 joining LUL bronchus

LB8

RB8

CARINA

RC2

LC2

RB1RB3

RB8

ML Bronchus

LB4

LB3

RB3

RB5RB4

LB5

LB3

VASCULAR ANATOMY ON CT THORAX

Rt. CCA

Rt. IJV

Rt. EJV

Lt. IJV

Lt. EJV

Lt. CCA

Rt. BCV

Rt. SCV joining Rt. BCV

Rt. CCA

Lt. CCA Lt.

SCV

Rt. SCA Lt.

SCA

Lt. BCV joining Rt. BCV

Rt. BCV

Rt. BCA

Lt. CCA Lt. SCA

SUPRA AORTIC LEVEL

Formation of SVC

Branching from Aortic Arch

AORTIC ARCH

SVC

AORTIC ARCH LEVEL

Ascending AORTA

Main Pulmonary Trunk

SVC

Right Pulmonary Trunk

Left Pulmonary Trunk

Descending AORTA

Aorta arising from Left Ventricle

Pulmonary Trunk arising from Right Ventricle

SVC draining into Right Atrium

Pulmonary Veins draining into Left Atrium

Pulmonary Veins

RVLV

LA

RA

RVLV

IVS

DA

IVC

RV LV

DA

LYMPH NODE STATIONS ON CT THORAX

LYMPH NODES STATION IN THORAX

1. SUPRACLAVICULAR NODES 

• LOW CERVICAL • SUPRACLAVICULAR• STERNAL NOTCH

Extends from the lower margin of the cricoid cartilage to the clavicles and the upper border of the manubrium.

The midline of the trachea serves as border between 1R and 1L.

2. UPPER PARATRACHEAL NODES

2R. Upper Right ParatrachealExtends to the left lateral border of the trachea. From upper border of manubrium to the intersection of caudal margin of innominate (left brachiocephalic) vein with the trachea.2L. Upper Left ParatrachealFrom the upper border of manubrium to the superior border of aortic arch.2L nodes are located to the left of the left lateral border of the trachea. 

3A. Pre-vascularThese nodes are not adjacent to the trachea like the nodes in station 2, but they are anterior to the vessels. 

3P. Pre-vertebralThese nodes are not adjacent to the trachea like the nodes in station 2, but behind the esophagus, which is prevertebral. 

4. LOWER PARATRACHEAL NODES

4R. Lower Right Paratracheal From the intersection of the caudal margin of in nominate (left brachiocephalic) vein with the trachea to the lower border of the azygos vein.4R nodes extend from the right to the left lateral border of the trachea. 

4L. Lower Left Paratracheal From the upper margin of the aortic arch to the upper rim of the left main pulmonary artery.

5-6. AORTIC NODES

5. Subaortic nodesThese nodes are located in the AP window lateral to the ligamentum arteriosum. These nodes are not located between the aorta and the pulmonary trunk but lateral to these vessels.

6. Para-aortic nodesThese are ascending aorta or phrenic nodes lying anterior and lateral to the ascending aorta and the aortic arch.

Inferior Mediastinal Nodes 7-9

7. Subcarinal nodes Nodes below carina

8. Paraesophageal nodes Nodes lateral to esophagus

9. Pulmonary Ligament nodes Nodes lying within the pulmonary ligaments.

Hilar, Lobar and (sub)segmental Nodes 10-14

These are all N1-nodes.10. Hilar nodesThese include nodes adjacent to the main stem bronchus and hilar vessels. 

On the right they extend from the lower rim of the azygos vein to the interlobar region. On the left from the upper rim of the pulmonary artery to the interlobar region.

DR. HARSHIL A. KALARIA RESIDENT,.

DEPARTMENT OF RADIOLOGY

UNDERSTANDING HRCT CHESTPart II: HRCT FINDINGS OF LUNG DISEASE

Q.1. What is the dominant HR-pattern ?

Q.2. Where is it located within the secondary lobule (centrilobular, Perilymphatic or random) ?

Q.3. Is there an upper versus lower zone or a central versus peripheral predominance ?

Q.4. Are there additional findings (pleural fluid, lymphadenopathy, traction bronchiectasis) ?

STRUCTURED APPROACH

158

INCREASED LUNG ATTENUATIONLINEAR AND RETICULAR OPACITIES

NODULES AND NODULAR OPACITIES

PARENCHYMAL OPACIFICATION

consolidation

Ground glass

DECREASED LUNG ATTENUATIONCYSTIC LESIONS, EMPHYSEMA, AND BRONCHIEACTASIS

MOSAIC ATTENUATION AND PERFUSION

AIR TRAPPING ON EXPIRATORY SCANS160

Attenuation pattern

High Attenuation pattern

GROUND GLASSCONSOLIDATION

Low Attenuation pattern

Emphysema Lung cysts Bronchiectasis Honeycombing

LINEAR AND RETICULAR OPACITIESRepresents

thickening of interstitial fibers of lung by

- fluid or - fibrous tissue

or - infiltration by

cells

162

Interface sign

Irregular interfaces between the aerated lung parenchyma and bronchi, vessels, or visceral pleural surfaces.

Represent thickened interlobular septa, intralobular lines, or irregular scars.Nonspecific.

Common in patients with an interstitial abnormality, fibrotic lung disease.

163

Peribronchovascular Interstitial Thickening

PBIT

Smooth

Pulmonary edema/ hemorrhage

Lymphoma / leukemia

Lymphangitic spread of carcinoma

Nodular

Sarcoidosis

Lymphangitic spread of carcinoma

Irregular

Due to adjacent lung fibrosis

Sarcoidosis, silicosis, TB and talcosis

Venous, lymphatic or infiltrative

disease

lymphatic or

infiltrative diseases

164

sarcoidosis

UNILATERAL LYMPHANGITIC SPREAD OF CARCINOMA

165

INTERLOBULAR SEPTAL THICKENINGNormally, only a few septa seen

On HRCT, if numerous interlobular septas are seen, it almost always indicate abnormality.

Septal thickening d/t -interstitial fluid, cellular infiltration or fibrosis.

The thickened interstitium outline the secondary pulmonary lobules and are perpendicular to the pleura.

D/D are similar to that of PBIT.

166

Smooth Septal thickening

Septal thickening and ground-glass opacity with a gravitational distribution in a patient with cardiogenic pulmonary edema.

167

Nodular Septal thickening

Focal septal thickening in lymphangitic carcinomatosis

Lymphangitic carcinomatosis : show diffuse smooth and nodular septal thickening.

Sarcoidosis : right lung base shows interlobular septal thickening associated with several septal nodules giving beaded appearance

168

Intralobular interstitial thickening (Intralobular lines)

Results in a fine reticular pattern on HRCT, with the visible lines separated by a few millimeters

Fine lace- or netlike appearance

Causes : Pulmonary fibrosis Asbestosis Chronic Eosinophilic

pneumonitis.

169

PARENCHYMAL BANDSNon tapering , reticular opacity

usually 1 to 3 mm in thickness and from 2 to 5 cm in length.

Is often peripheral and generally contracts the pleural surface

D/D : 1. Asbestosis 2. Sarcoidosis 3. Silicosis/ coal worker

pneumoconiosis 4. Tuberculosis with

associated scarring.

170

Subpleural Interstitial ThickeningMimic thickening of fissure.DD similar to that of

interlobular septal thickening.

more common than septal thickening in Idiopathic Pulmonary Fibrosis or UIP of any cause.

171

Size, Distribution, AppearanceNodules and Nodular Opacities

Size

Small Nodules: <10 mm Miliary - <3 mm

Large Nodules: >10 mm Masses - >3 cms

Appearance

Interstitial opacity: Well-defined, homogenous,Soft-tissue densityObscures the edges of vessels or adjacent structure

Air space: Ill-defined, inhomogeneous.Less dense than adjacent vessel – GGOsmall nodule is difficult to identify

172

Interstitial nodules

Air space opacity

173

Miliary tuberculosis

sarcoidosis

in a lung transplant patient with bronchopneumonia

RANDOM: no consistent relationship to any structures

PERILYMPHATIC: corresponds to distribution of lymphatics

CENTRILOBULAR: related to centrilobular structuresDistribution

174

Perilymphatic distribution Nodules in relation to pulmonary lymphatics

at # perihilar peribronchovascular

interstitium, # interlobular septa, # subpleural regions, and # centrilobular interstitium.

175

Perilymphatic nodules: D/D

Sarcoidosis

Lymphangitic carcinomatosis

Lymphocytic interstitial pneumonia (LIP)

Lymphoproliferative disorders

Amyloidosis176

Centrilobular nodulesDistributed primarily within

the centre of the secondary pulmonary lobule

Reflect the presence of either interstitial or airspace abnormalities

Dense or ground-glass opacity

Subpleural lung is typically spared- distinguishes from

diffuse random nodules. 177

Tree-in-budCentrilobular nodules m/b further characterized by presence

or absence of ‘‘tree-in-bud.’’

Tree-in-bud -- Impaction of centrilobular bronchus with mucous, pus, or fluid, resulting in dilation of the bronchus, with associated peribronchiolar inflammation .

Dilated, impacted bronchi produce Y- or V-shaped structures

This finding is almost always seen with pulmonary infections.

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179

180

Centrilobular nodules with or without tree-in-bud opacity: D/D :

With tree-in-bud opacity

Bacterial pneumoniaTypical and atypical

mycobacteria infectionsBronchiolitisDiffuse panbronchiolitisAspiration Allergic

bronchopulmonary aspergillosis

Cystic fibrosisEndobronchial-

neoplasms (particularlyBronchioloalveolar

carcinoma)

Without tree-in-bud opacity

All causes of centrilobular nodules with tree-in-bud opacity

Hypersensitivity pneumonitis

Respiratory bronchiolitis Cryptogenic organizing

pneumoniaPneumoconiosesLangerhans’ cell

histiocytosisPulmonary edemaVasculitisPulmonary hypertension

181

Random nodulesRandom nodules – No definable distribution

Are usually distributed uniformly throughout the lung parenchyma in a bilaterally symmetric distribution.

Random nodules: Miliary tuberculosis.

Axial HRCT image shows multiple nodules scattered uniformly throughout the lung parenchyma.

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Random nodules: D/D

1. Haematogenous metastases2. Miliary tuberculosis3. Miliary fungal infection4. Disseminated viral infection5. Silicosis or coal-worker’s

pneumoconiosis6. Langerhans’ cell histiocytosis

185

Parenchymal Opacification

Ground-glass opacity

Consolidation

Lung calcification & high attenuation opacities.

186

GROUND GLASS OPACITIESHazy increased attenuation of lung,

with preservation of bronchial and vascular margins

Pathology : it is caused by # partial filling of air spaces, # interstitial thickening, # partial collapse of alveoli, # normal expiration, or # increased capillary blood

volumeD/t volume averaging of

morphological abnormality too small to be resolved by HRCT

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IMPORTANCE OF GGOCan represent - microscopic interstitial disease(alveolar interstitium) - microscopic alveolar space disease - combination of both

In the absence of fibrosis, mostly indicates the presence of an ongoing, active, potentially treatable process

Ground Glass opacity should be diagnosed only on scans obtained with thin sections : with thicker sections volume averaging is more - leading to spurious GGO, regardless of the nature of abnormality

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DIFFERNTIAL DIAGNOSIS : GGO

189

The location of the abnormalities in ground glass pattern can be helpful:

Upper zone predominance: Respiratory bronchiolitis PCP.

Lower zone predominance: UIP, NSIP, DIP.

Centrilobular distribution: Hypersensitivity

pneumonitis, Respiratory bronchiolitis

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GGO with few cystic and reticular lesion in HIV + ve patient -- PCP

Combination of GGO with fibrosis and tractional bronchiectasis-- NSIP

191

CRAZY PAVING PATTERNIt is scattered or diffuse ground-glass

attenuation with superimposed interlobular septal thickening and intralobular lines.

Causes:

192

Combination of ground glass opacity and septal thickening : Alveolar proteinosis.

193

194

CONSOLIDATIONConsolidation is defined as increased attenuation, which results in

obscuration of the underlying vasculature, usually producing air bronchogram.

The presence of consolidation implies that the air within affected alveoli has been replaced by another substance, such as blood, pus, oedema, or cells.

When consolidation is evident on a chest radiograph, HRCT does not usually provide additional diagnostically useful information.

D/D on the basis of presentationAcute consolidation is seen in: - Pneumonias (bacterial, mycoplasma , PCP) - Pulmonary edema due to heart failure or ARDS - Hemorrhage - Acute eosinophilic pneumonia

Chronic consolidation is seen in: - Organizing Pneumonia - Chronic eosinophilic pneumonia - Fibrosis in UIP and NSIP - Bronchoalveolar carcinoma or lymphoma

195

196

Patchy ground-glass opacity, consolidation, and nodule mainly with peribronchovascular distribution with reversed halo signs (central ground-glass opacity and surrounding air-space consolidation)

Peripheral consolidations with upper lobe predominance (photo negative of pulmonary edema)

Lung calcification & high attenuation opacities Multifocal lung calcification • Infectious granulomatous ds - TB,

histoplasmosis, and varicella, pneumonia; • Sarcoidosis , silicosis, AmyloidosisFat embolism associated with ARDS

Diffuse & dense lung calcification • Metastatic calcification, • Disseminated pulmonary ossification, or • Alveolar microlithiasis

197

High attenuation opacity • Talcosis asso with fibrotic mass, • inhalation of metals (tin/barium)

Small focal areas of increased attenuation • injection and embolized radiodense materials

such as mercury or acrylic cement Diffuse, increased lung attn in absence of

calcification • amiodarone lung toxicity or • embolization of iodinated oil after

chemoembolization 198

199

HRCT findings manifesting as decreased lung opacity

Lung Cysts,

Emphysema,

and

Bronchiectasis

200

HONEYCOMBINGDefined as - small cystic spaces with irregularly

thickened walls composed of fibrous tissue.

Predominate in the peripheral and subpleural lung regions

Subpleural honeycomb cysts typically occur in several contiguous layers. D/D- paraseptal emphysema in which subpleural cysts usually occur in a single layer.

Indicates the presence of “END stage” disease regardless of the cause.

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Causes

Lower lobe predominance : 1. UIP or interstitial fibrosis 2. Connective tissue disorders 3. Hypersensitivity pneumonitis 4. Asbestosis 5. NSIP (rare)

Upper lobe predominance : 1. End stage sarcodosis 2. Radiation 3. Hypersensitivity Pneumonitis 4. End stage ARDS

202

Honeycombing and traction bronchiectasis in UIP.

Lung cystsThin walled (less than 3mm) , well defined and

circumscribed air containing lesions They are lined by cellular epithelium, usually

fibrous or epithelial in nature.Common cause are : 1. Lymphangiomyomatosis 2. Langerhans

Histiocytosis 3. Lymphoid interstitial

pneumonia They need to be differentiated from

emphysematous bullae, blebs and pneumatocele.204

Axial HRCT image through the upper lobes shows multiple bilateral bizarre-shaped cysts and small centrilobular nodules in a smoker with Langerhans’ cell histiocytosis.

Axial HRCT image through the upper lobes shows multiple bilateral uniform, thin-walled cysts.

205

BRONCHIEACTASISBronchiectasis is defined as localized, irreversible

dilation of the bronchial tree.

HRCT findings of the bronchiectasis include

# Bronchial dilatation # Lack of bronchial tapering # Visualization of peripheral airways.

206

BRONCHIAL DILATATION # The broncho-arterial ratio (internal diameter of

the bronchus /pulmonary artery) exceeds 1. # In cross section it appears as “Signet Ring

appearance”

LACK OF BRONCHIAL TAPERING # The earliest sign of cylindrical bronchiectasis # One indication is lack of change in the size of an

airway over 2 cm after branching.

VISUALIZATION OF PERIPHERAL AIRWAYS # Visualization of an airway within 1 cm of the

costal pleura is abnormal and indicates potential bronchiectasis

207

Coned axial HRCT image shows bronchial dilation with lack of tapering . Bronchial morphology is consistent with varicose bronchiectasis.

208

A NUMBER OF ANCILLARY FINDINGS ARE ALSO RECOGNIZED:

# Bronchial wall thickening : normally wall of bronchus should be less than half the width of the accompanying pulmonary artery branch.

# Mucoid impaction # Air trapping and mosaic perfusion

Extensive, bilateral mucoid impaction Mosaic perfusion caused by large and

small airway obstruction.Small centrilobular nodules are visible

in the right lower lobe

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Types 1. CYLINDRICAL

BRONCHIECTASIS # mildest form of this disease, # thick-walled bronchi that

extend into the lung periphery and fail to show normal tapering

2. VARICOSE BRONCHIECTASIS # beaded appearance of

bronchial walls - dilated bronchi with areas of relative narrowing

# string of pearls. # Traction bronchiectasis often

appears varicose. 210

3. CYSTIC BRONCHIECTASIS :

# Group or cluster of air-filled cysts,

# cysts can also be fluid filled, giving the appearance of a cluster of grapes.

4.TRACTION BRONCHIECTASIS :

# Defined as dilatation of intralobular bronchioles because of surrounding fibrosis

# due to fibrotic lung diseases

211

Tram Tracks

ABPA: glove-finger shadow due to mucoid impaction in central bronchiectasis in a patient with asthma.

Differential diagnosis1. Infective causes : specially childhood

pneumonia, pertusis, measles, tuberculosis

2. Non- infective causes : Bronchopulmonary aspergillosis, inhalation of toxic fumes

3. Connective tissue disorder : Ehlers-Danlos Synd,

Marfan synd , tracheobronchomeglay

4. Ciliary diskinesia : Cystic fibrosis, Kartangener synd, agammaglobulinemia .

5. Tractional bronchiectasis in interstitial fibrosis.

214

EMPHYSEMA Permanent, abnormal enlargement of air

spaces distal to the terminal bronchiole and accompanied by the destruction of the walls of the involved air spaces.

215

Centrilobular (proximal or centriacinar) emphysema Found most commonly in the upper lobes Manifests as multiple small areas of low attenuation without a

perceptible wall, producing a punched-out appearance. Often the centrilobular artery is visible within the centre of

these lucencies.

216

PANLOBULAR EMPHYSEMA Affects the entire secondary pulmonary lobule

and is more pronounced in the lower zonesComplete destruction of the entire pulmonary

lobule.Results in an overall decrease in lung

attenuation and a reduction in size of pulmonary vessels

217

Paraseptal (distal acinar) emphysemaAffects the peripheral parts of the secondary

pulmonary lobuleProduces subpleural lucencies.

218

Cicatricial Emphysema/ irregular air space enlargementpreviously known as irregular or cicatricial emphysema

• can be seen in association with fibrosis • with silicosis and progressive massive fibrosis or sarcoidosis

BULLOUS EMPHYSEMA :

• Does not represent a specific histological abnormality• Emphysema characterized by large bullae• Often associated with centrilobular and paraseptal emphysema

219

Paraseptal Emphysema vs HoneycombingParaseptal emphysema Honeycomb cysts

occur in a single layer at the pleural surface

may occur in several layers in the subpleural lung

predominate in the upper lobes

predominate at the lung bases

unassociated with significant fibrosis

Asso with other findings of fibrosis.

Associated with other findings of emphysema

Absent

220

Bullae A sharply demarcated area of emphysema ≥ 1 cm in diameter

a thin epithelialized wall ≤ 1 mm.

uncommon as isolated findings, except in the lung apices

Usually asso with evidence of extensive centrilobular or paraseptal emphysema

When emphysema is associated with predominant bullae, it may be termed bullous emphysema

221

Pneumatocele

Defined as a thin-walled, gas-filled space within the lung,

Associated with acute pneumonia or hydrocarbon aspiration.

• Often transient. • believed to arise from lung necrosis and

bronchiolar obstruction. • Mimics a lung cyst or bulla on HRCT and

cannot be distinguished on the basis of HRCT findings. 222

CAVITARY NODULEThicker and more

irregular walls than lung cysts

• In diffuse lung diseases - LCH, TB, fungal infections, and sarcoidosis.

Also seen in rheumatoid lung disease, septic embolism, pneumonia, metastatic tumor, tracheobronchial papillomatosis, and Wegener granulomatosis

Cavitary nodules or cysts in tracheobronchial papillomatosis.

fungal pneumonia 223

Mosaic attenuation & perfusionLung density and attenuation depends partially on

amount of blood in lung tissue.

The term 'mosaic attenuation' is used to describe density differences between affected and non-affected lung areas.

It is seen as inhomogeneous attenuation of lung parenchyma with focal region of lucency which show smaller size of vessels

May be due to vascular obstruction, abnormal ventilation or airway disease/

224

Mosaic attenuation due to small airway disease # Air trapping and bronchial dilatation commonly seen. # Areas of increased attenuation have relatively large

vessels, while areas of decreased attenuation have small vessels.

# Causes include: Bronchiectasis, cystic fibrosis and bronchiolitis obliterans.

Mosaic attenuation due to vascular disease # common in patients with acute or chronic pulmonary embolism (CPE), and # decreased vessel size in less opaque regions is often visible

225

MOSIAC PATTERN

DEPENDENT LUNG ONLY

PRONE POSITION

RESOLVE

PLATE ATELECTASI

S

NOT RESOLVE

GROUND GLASS

NONDEPENDENT LUNG

EXPIRATION

NO AIR TRAPPING

VESSEL SIZE

DECREASED

VASCULAR

NORMAL

GROUND GLASS

AIR TRAPPING

AIRWAYS

DISEASE

226

Inhomogeneous lung opacity: mosaic perfusion in a patient with bronchiectasis.

central bronchiectasis with multifocal, bilateral inhomogeneous lung opacity.

The vessels within the areas of abnormally low attenuation are smaller than their counterparts in areas of normal lung attenuation.

227

Air trapping on expirationMost patients with air trapping seen on

expiratory scans have inspiratory scan abnormalities, such as bronchiectasis, mosaic perfusion, airway thickening, or nodules suggest the proper differential diagnosis.

Occasionally, air trapping may be the sole abnormal finding on an HRCT study.

The differential diagnosis include --- bronchiolitis obliterans; asthma;

chronic bronchitis; and hypersensitivity pneumonitis

228

Air trapping on expiratory imaging in the absence of inspiratory scan findings in a patient with bronchiolitis obliterans.

(A) Axial inspiratory image through the lower lobes shows no clear evidence of inhomogeneous lung opacity.

(B) Axial expiratory image shows abnormal low attenuation (arrows) caused by air trapping, representing failure of the expected increase in lung attenuation that should normally occur with expiratory imaging.

229

Head cheese signIt refers to mixed densities which includes

presence of- # consolidation # ground glass opacities # normal lung # Mosaic perfusion

• Signifies mixed infiltrative and obstructive disease

• Common cause are : Hypersensitive pneumonitis Sarcoidosis DIP

230

Axial HRCT image in a patient with hypersensitivity pneumonitis shows a combination of ground-glass opacity, normal lung, and mosaic perfusion (arrow) on the same inspiratory image.

231

Distribution within the lung

Upper lung zone preference is seen in: 1.Inhaled particles: pneumoconiosis (silica or coal) 2.Smoking related diseases (centrilobular emphysema 3. Respiratory bronchiolitis (RB-ILD) 4.Langerhans cell histiocytosis 5.Hypersensitivity pneumonitis 6.Sarcoidosis

Lower zone preference is seen in: 1. UIP 2. Aspiration 3. Pulmonary edema 232

Central vs peripheral zone

Central Zone Peripheral zone

1. Sarcoidosis 1. COP 2. Cardiogenic pulmonary 2. Ch Eosinophilic

Pneumonia edema 3. UIP 3. Bronchitis 4. Hematogenous

mets

233

Additional findings

Pleural effusion is seen in:Pulmonary edema

Lymphangitic spread of carcinoma - often unilateral

Tuberculosis

Lymphangiomyomatosis (LAM)

Asbestosis

234

Hilar and mediastinal lymphadenopathy# In sarcoidosis the common pattern is right

paratracheal and bilateral hilar adenopathy ('1-2-3-sign').

# In lung carcinoma and lymphangitic carcinomatosis adenopathy is usually unilateral.

#'Eggshell calcification' in lymph nodes occurs in ----Silicosis and coal-worker's pneumoconiosis and is sometimes seen in sarcoidosis, post irradiation Hodgkin disease, blastomycosis and scleroderma .

235

Conclusion• A thorough knowledge of the basic anatomy is of utmost

importance.

When attempting to reach a diagnosis or differential diagnosis of lung disease using HRCT, the overall distribution of pulmonary abnormalities should be considered along with their morphology, HRCT appearance, and distribution relative to lobular structures.

Correlation of the radiological findings with patients clinical and laboratory findings to reach a likely diagnosis

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