Multidetector

row

CT

for

imaging

the

paediatric

tracheobronchial

tree

The

introduction

of

multidetector

row

computed

tomography

-LRB-

MDCT

-RRB-

scanners

has

altered

the

approach

to

imaging

the

paediatric

thorax

In

an

environment

where

the

rapid

acquisition

of

CT

data

allows

general

hospitals

to

image

children

instead

of

referring

them

to

specialist

paediatric

centres

it

is

vital

that

general

radiologists

have

access

to

protocols

appropriate

for

paediatric

applications

Thus

a

dramatic

reduction

in

the

delivered

radiation

dose

is

ensured

with

optimal

contrast

bolus

delivery

and

timing

and

inappropriate

repetition

of

the

scans

is

avoided

This

article

focuses

on

the

main

principles

of

volumetric

CT

imaging

that

apply

generically

to

all

MDCT

scanners

We

describe

the

reconstruction

techniques

for

imaging

the

paediatric

thorax

and

the

low-dose

protocols

used

in

our

institution

on

a

detector

CT

scanner

Examples

of

the

commonest

clinical

applications

are

also

given

Introduction

Imaging

of

the

airways

with

subsequent

and

reconstructions

has

significantly

improved

with

the

advent

of

the

multidetector

row

computed

tomography

-LRB-

MDCT

-RRB-

scanners

These

scanners

allow

volumetric

acquisition

of

isotropic

datasets

As

a

result

the

scanning

time

is

significantly

reduced

and

large

anatomical

regions

are

covered

within

seconds

with

optimal

intravenous

contrast

material

enhancement

MDCT

scanners

have

significantly

improved

the

image

quality

as

the

artefacts

resulting

from

partial

volume

averaging

and

motion

have

been

dramatically

reduced

Additionally

their

fast

and

user-friendly

workstations

allow

postprocessing

of

impressive

multiplanar

and

reconstructions

which

are

desirable

to

clinicians

as

they

can

be

used

for

comprehensive

presurgical

planning

-LSB-

-RSB-

In

chest

applications

the

whole

of

the

tracheobronchial

tree

can

be

adequately

depicted

with

a

single-breath-hold

volume

acquisition

within

s

normal

or

complex

anatomical

structures

pathological

processes

and

their

anatomical

relationships

can

be

precisely

imaged

-LSB-

-RSB-

Finally

on

the

MDCT

scanner

by

applying

the

Combiscan

protocol

-LRB-

collimated

scans

after

administration

of

intravenous

contrast

medium

-RRB-

postprocessing

of

the

original

data

pool

can

additionally

generate

high-resolution

images

of

the

chest

Technicalities

for

MDCT

of

the

paediatric

airways

Imaging

of

the

airways

and

thoracic

vessels

in

infants

and

children

has

been

significantly

affected

by

the

wide

spectrum

of

applications

of

MDCT

The

key

achievement

with

MDCT

is

the

increased

volume

coverage

per

time

unit

at

high

axial

resolution

which

results

in

improved

temporal

resolution

With

MDCT

scanning

techniques

may

vary

when

different

collimation

is

selected

the

narrowest

collimation

is

applied

when

partial

volume

effect

needs

to

be

minimal

and

the

postprocessing

images

of

optimal

quality

e.g.

CT

angiography

-LRB-

CTA

-RRB-

and

cardiac

CT

-LSB-

-RSB-

Preparation

of

the

child

is

sedation

always

needed

Due

to

the

faster

scanning

times

possible

with

MDCT

scanners

routine

sedation

is

no

longer

required

In

the

neonate

recent

feeding

usually

provides

tranquillity

while

children

over

years

of

age

tend

to

cooperate

after

explanation

of

the

procedure

through

play

therapy

and

verbal

reassurance

As

a

result

CT

waiting

lists

have

shortened

Which

protocol

should

be

applied

Planning

the

examination

protocol

is

essential

as

this

will

provide

the

optimal

imaging

results

that

will

lead

to

an

accurate

diagnosis

Suggested

paediatric

protocols

applied

in

our

institution

are

displayed

in

Tables

and

Table

protocol

for

the

paediatric

chest

using

a

MDCT

scanner

Routine

scanCombiscan/CTAIndicationStrictureCardiovascular

anomaliesTumourSmall

tracheobronchial

stenosesTracheomalaciaPeripheral

airways

diseaseAnatomical

areaThoracic

inlet

to

diaphragmTube

collimation

-LRB-

mm

-RRB-

Slice

width

reconstructed

-LRB-

mm

-RRB-

feed

-LRB-

mm/rotation

-RRB-

effective

mAs

-LRB-

dependent

on

patient

weight

-RRB-

effective

mAs

-LRB-

dependent

on

patient

weight

-RRB-

s

scan

s

scan

timeRespirationSuspended

inspiration

single

breath-hold

where

possibleThree

to

five

expiratory

scans

for

tracheomalacia/small

airways

diseaseContrast

mediumNoneYesTriggering

for

CTAAlgorithmSoft

tissueSoft

tissue

plus

reconstruction

on

bony

algorithm

for

high-resolution

CT

of

the

lungsTable

delay

times

from

the

injection

of

contrast

medium

Manual

injectionPressure

injectorScan

initiationtime

s

from

termination

of

s

from

start

of

injectionFlow

ml/sAge

rangeAll

age

groupsAll

age

groupsTable

CT

chest

scanning

parameters

according

to

child

's

weight

when

routine

and

Combiscan

protocols

are

performed

-LRB-

mm

-RRB-

Scan

slice

width

-LRB-

mm

-RRB-

feed

-LRB-

mm

-RRB-

time

-LRB-

s

-RRB-

Calculated

Effective

Dose

-LRB-

mSv

-RRB-

CT

Table

CT

chest

scanning

parameters

according

to

child

's

weight

kg

-LRB-

mm

-RRB-

slice

width

-LRB-

mm

-RRB-

feed

-LRB-

mm

-RRB-

time

-LRB-

s

-RRB-

Calculated

Effective

Dose

-LRB-

mSv

-RRB-

CT

Table

angiography

scanning

parameters

according

to

child

's

weight

-LRB-

mm

-RRB-

Scan

slice

width

-LRB-

mm

-RRB-

feed

-LRB-

mm

-RRB-

time

-LRB-

s

-RRB-

Calculated

Effective

Dose

-LRB-

mSv

-RRB-

CT

Radiation

dose

When

dealing

with

children

the

issue

of

performing

a

low-dose

examination

is

crucial

and

of

the

utmost

importance

Radiation

dose

is

a

significant

issue

in

paediatrics

as

it

is

well

established

that

the

life-time

cancer

mortality

risk

attributable

to

CT

examinations

is

considerably

higher

than

in

adults

-LSB-

-RSB-

As

proposed

by

the

ALARA

principle

the

selection

of

appropriate

scanning

parameters

focuses

on

the

optimization

of

the

image

quality

whilst

delivering

the

lowest

possible

radiation

dose

and

shifting

the

risk

benefit

balance

towards

benefit

-LSB-

-RSB-

Technical

parameters

that

need

to

be

selected

for

any

scan

include

thickness

of

collimation

tube

current

and

kilovoltage

The

thickness

of

collimation

is

the

minimum

section

thickness

that

can

be

acquired

once

the

scan

is

finished

and

in

a

MDCT

scanner

is

usually

mm

Thinner

collimation

-LRB-

mm

-RRB-

increases

the

radiation

dose

by

approximately

with

our

in-house

reduced

protocol

and

is

applied

only

in

selected

cases

of

vascular

abnormalities

visualization

of

small

structures

and

in

cardiac

CT

-LRB-

Tables

and

-RRB-

The

axial

images

are

reconstructed

at

thickness

and

archived

to

the

PACS

system

within

our

hospital

In

recent

years

we

have

made

efforts

to

standardize

low-dose

protocols

for

the

children

scanned

in

our

institution

and

the

currently

applied

parameters

are

summarized

in

the

Tables

and

Methods

adopted

to

minimize

radiation

dose

in

MDCT

include

Applying

a

dose

modulation

function

where

the

system

samples

the

patient

thickness

and

adjusts

-LRB-

i.e.

reduces

-RRB-

the

exposure

accordingly

when

the

tube

is

in

the

AP/PA

position

as

patients

are

narrower

in

the

frontal

than

in

the

side-to-side

orientation.Reduction

of

the

kilovoltage

to

kVp

when

imaging

the

thorax

Further

reduction

to

kVp

is

possible

for

CTA

but

as

resolution

of

the

parenchyma

is

not

ideal

this

is

applied

only

if

lung

pathology

is

unlikely.Selecting

tube

collimation

of

mm

The

collimation

improves

spatial

resolution

but

as

already

mentioned

increases

the

radiation

dose

and

is

therefore

reserved

for

CTA

or

where

thin-slice

reconstruction

is

indicated.Selecting

appropriate

mAs

selection

dependent

on

the

patient

's

weight

or

cross-sectional

diameter.Table

comparison

for

different

scanning

protocols

in

a

phantom

study

in

our

institutionWeight

range

-LRB-

kg

-RRB-

Effective

dose

-LRB-

mSv

-RRB-

Volume

-LRB-

mm

-RRB-

Combi

-LRB-

mm

-RRB-

High-resolution

CTCTAChest

radiographyMaleFemaleMaleFemaleMaleFemaleMaleFemaleAPLateral

150.770.900.91.050.360.421.301.510.004870.0079915

240.931.091.131.310.360.421.621.890.008740.0108625

341.341.561.581.840.540.632.242.620.011630.0096835

442.112.462.482.891.001.172.573.00.017690.01452

Unlike

the

single-slice

scanner

an

increase

or

decrease

in

table

feed

time

on

the

MDCT

scanner

only

affects

the

overall

scanning

time

An

increase

in

table

speed

results

in

a

concomitant

increase

in

mA

and

this

has

no

effect

on

the

dose

delivered

The

tube

current

is

automatically

compensated

to

ensure

that

the

preset

effective

and

total

mAs

is

delivered

i.e.

a

fast

table

movement

results

in

an

automatic

increase

in

the

mA

keeping

the

mAs

constant

Anatomical

coverage

For

imaging

of

the

paediatric

thorax

regular

coverage

extends

from

the

thoracic

inlet

to

the

diaphragm

Greater

coverage

may

be

warranted

in

certain

clinical

cases

such

as

an

extralobar

pulmonary

sequestration

that

may

derive

its

blood

supply

from

the

upper

abdomen

In

order

to

increase

spatial

resolution

the

field

of

view

-LRB-

FOV

-RRB-

should

closely

approximate

the

cross-sectional

area

of

the

body

part

being

studied

A

large

FOV

would

result

in

waste

of

matrix

space

and

partial

volume

averaging

would

generate

poor

quality

images

-LSB-

-RSB-

Breathing

during

scan

Ideally

scans

should

be

performed

during

suspended

inspiration

at

total

lung

capacity

but

this

is

not

often

possible

in

younger

children

Experience

has

proved

quiet

breathing

to

be

more

successful

than

the

confusion

created

over

attempts

to

acquire

the

scans

during

suspended

inspiration

-LSB-

-RSB-

When

subtle

air-trapping

due

to

small

airways

disease

is

suspected

a

few

supplementary

expiratory

sections

may

be

obtained

If

the

child

is

too

young

to

breath-hold

decubitus

scans

may

replace

expiratory

scans

the

dependent

lung

behaving

as

the

expiratory

lung

and

the

nondependent

lung

behaving

as

the

inspiratory

lung

-LSB-

-RSB-

The

acquisition

of

prone

scans

is

rarely

required

in

older

children

who

may

demonstrate

hypoventilation

changes

in

the

dependent

areas

of

the

lungs

General

anaesthesia

is

therefore

applied

only

in

a

limited

number

of

cases

Contrast

medium

When

imaging

the

airways

intravenous

nonionic

contrast

material

is

only

administered

if

paratracheal

abnormalities

such

as

vascular

rings

anomalous

origin

of

the

pulmonary

artery

and

mediastinal

masses

are

suspected

-LSB-

-RSB-

Combiscans

provide

the

potential

to

image

equally

well

the

lung

parenchyma

by

using

the

high-resolution

techniques

-LRB-

HR

-RRB-

for

reconstruction

algorithms

and

the

mediastinal

structures

by

injecting

contrast

medium

However

since

fine

collimation

is

required

there

is

an

inevitable

increase

in

the

radiation

dose

-LRB-

Table

-RRB-

and

its

application

is

limited

to

cases

where

lung

parenchymal

detail

is

of

high

importance

An

intravenous

cannula

should

preferably

be

placed

in

situ

on

the

ward

so

that

the

child

will

not

associate

CT

with

venepuncture

especially

in

those

in

whom

subsequent

scans

may

be

required

It

is

ideally

inserted

via

a

peripheral

vein

of

the

upper

or

lower

limb

Central

lines

are

used

for

injection

in

conjunction

with

clinical

agreement

and

are

more

desirable

as

the

experience

is

less

unpleasant

for

the

child

than

having

to

undergo

repeated

cannulation

Nonionic

contrast

medium

is

administered

at

a

dose

of

ml/kg

up

to

a

maximum

of

ml

via

a

cannula

using

either

a

power

injector

or

hand

injection

-LRB-

when

the

cannula

is

placed

in

the

hand

or

the

wrist

-RRB-

The

power

injector

has

the

advantage

of

instilling

contrast

medium

at

a

constant

delivery

rate

A

flow-rate

of

ml/s

is

used

rising

to

ml/s

for

cardiac

studies

The

delay

time

between

the

start

of

injection

and

the

start

of

the

scan

can

be

empirical

and

bolus

tracking

is

routinely

used

in

cardiac

CT

studies

-LRB-

Table

-RRB-

In

children

with

complex

vascular

anatomy

the

radiologist

should

be

present

for

the

examination

In

those

children

low-dose

planning

scans

are

performed

at

a

predetermined

anatomical

level

and

the

injection

of

contrast

medium

is

triggered

by

the

radiologist

The

volumetric

scan

begins

when

the

contrast

medium

has

reached

the

relevant

preselected

vascular

structure

Postprocessing

There

are

four

reconstruction

displays

available

for

postprocessing

of

the

volumetric

data

which

are

applied

accordingly

multiplanar

reformation

or

reconstruction

-LRB-

MPR

-RRB-

shaded-surface

display

-LRB-

SSD

-RRB-

multiprojective

volume

reconstruction

-LRB-

MPVR

-RRB-

and

volume

rendering

-LRB-

VR

-RRB-

In

fact

the

axial

images

include

all

the

information

about

the

anatomy

of

the

airways

that

is

provided

with

and

reformats

However

postprocessing

gives

added

value

to

imaging

since

the

axial

scans

that

need

to

be

studied

are

usually

numerous

and

oblique

structures

as

well

as

interfaces

and

surfaces

parallel

to

the

axial

plane

are

poorly

demonstrated

and

sometimes

occult

Multiplanar

reformations

These

provide

additional

diagnostic

information

in

different

planes

and

are

as

accurate

as

the

axial

scans

due

to

the

nature

of

the

isovolumetric

acquisition

of

the

data

-LSB-

-RSB-

MPRs

are

one-voxel-thick

tomographic

sections

that

can

be

displayed

in

coronal

sagittal

or

parasagittal

planes

or

in

a

single

tomographic

curved

plane

along

the

axis

of

a

structure

of

interest

e.g.

a

bronchus

or

a

feeding

vessel

-LRB-

Figs.

and

-RRB-

-LSB-

-RSB-

They

are

real-time

easy-to-reconstruct

images

producible

as

soon

as

the

axial

sections

are

completed

They

generally

improve

our

perception

of

images

and

give

information

that

although

contained

in

transverse

images

is

sometimes

less

effectively

displayed

Their

diagnostic

value

is

substantial

in

demonstrating

and

documenting

the

presence

of

small

focal

lesions

defining

the

vertical

extent

of

a

bronchial

stenosis

which

may

go

undiagnosed

from

the

axial

source

CT

images

-LRB-

Figs.

and

-RRB-

and

are

invaluable

prior

to

surgical

remodelling

of

vascular

rings

and

the

tracheobronchial

tree

-LSB-

-RSB-

However

to

avoid

misinterpretations

due

to

partial

volume

effect

e.g.

overestimation

of

the

degree

of

a

stenosis

overlapping

and

thinner

cuts

should

be

applied

when

processing

the

raw

data

Likewise

when

processing

curved

MPRs

the

trace

should

be

centred

within

the

lumen

of

interest

to

avoid

anatomical

distortion

Fig.

oblique

MPR

in

boy

with

trisomy

There

is

right

lung

hypoplasia

and

diaphragmatic

eventration

An

incidental

finding

is

an

aberrant

right

subclavian

artery

-LRB-

arrow

-RRB-

Fig.

MPR

of

the

chest

in

a

child

with

a

history

of

recurrent

infections

due

to

a

congenital

pulmonary

airway

malformation

A

thin-walled

multicystic

lesion

in

the

right

lower

lobe

is

shownFig

in

an

child

with

a

congenital

pulmonary

airway

malformation

in

the

right

lower

lobe

a

Coronal

MPR

in

lung

window

setting

shows

the

air-filled

cystic

component

of

the

lesion

b

c

Axial

CT

slice

-LRB-

b

-RRB-

and

coronal

MPR

-LRB-

c

-RRB-

showing

a

large

arterial

feeder

-LRB-

arrow

-RRB-

This

is

however

visualized

and

appreciated

better

with

an

oblique

MIP

along

the

axis

of

the

vessel

-LRB-

d

-RRB-

and

with

coronal

anterior

and

posterior

VR

-LRB-

e

-RRB-

These

images

additionally

demonstrate

the

pulmonary

venous

drainage

of

the

lesion

i.e.

intralobar

sequestration

-LRB-

curved

arrows

-RRB-

Fig.

tracheal

stenosis

in

a

girl

with

trisomy

a

Series

of

axial

slices

demonstrating

stenosis

in

the

central

third

of

the

trachea

b

This

is

more

sensitively

demonstrated

on

coronal

MPR

which

correlates

well

with

the

bronchographic

appearances

-LRB-

c

-RRB-

-LRB-

arrows

-RRB-

d

Virtual

bronchoscopy

also

demonstrates

mild

stenosis

of

the

supracarinal

portion

of

the

trachea

-LRB-

arrowheads

-RRB-

Fig.

CT

-LRB-

mm

collimation

following

intravenous

injection

of

contrast

medium

-RRB-

in

boy

with

recurrent

wheezing

due

to

congenital

tracheal

stenosis

treated

previously

with

tracheoplasty

There

is

mild

stenosis

of

the

trachea

and

the

origin

of

the

right

main

bronchus

which

is

appreciated

with

difficulty

on

the

axial

scans

-LRB-

a

-RRB-

but

is

nicely

shown

in

coronal

MPR

-LRB-

arrow

-RRB-

-LRB-

b

-RRB-

Virtual

bronchoscopy

in

this

case

was

unnecessary

Bronchography

-LRB-

c

-RRB-

and

bronchoscopy

confirmed

stenosis

in

the

right

main

bronchus

-LRB-

arrow

-RRB-

that

was

caused

by

granulation

tissueFig

CT

-LRB-

collimation

after

intravenous

injection

of

contrast

medium

-RRB-

in

a

girl

with

absent

pulmonary

valve

syndrome

a

Axial

contrast-enhanced

CT

shows

massive

dilatation

of

the

main

and

the

left

pulmonary

arteries

with

possible

compression

of

the

left

main

bronchus

This

is

also

appreciated

on

serial

oblique

MIPs

-LRB-

b

-RRB-

but

becomes

more

apparent

on

the

oblique

MIP

along

the

axis

of

the

left

main

bronchus

-LRB-

c

-RRB-

-LRB-

black

arrow

-RRB-

and

on

the

VR

-LRB-

d

-RRB-

-LRB-

white

arrow

-RRB-

Fig.

of

the

chest

in

girl

with

laryngeal/pulmonary

papillomatosis

a

There

is

irregular

thickening

and

narrowing

of

the

proximal

tracheal

wall

that

is

well

demonstrated

on

axial

imaging

b

c

Coronal

MPRs

additionally

demonstrate

intrapulmonary

cavitating

lesions

Same

findings

are

impressively

demonstrated

on

VR

-LRB-

d

-RRB-

Fig.

tumour

in

a

child

with

a

history

of

cough

and

haemoptysis

Axial

imaging

-LRB-

a

-RRB-

and

coronal

-LRB-

b

-RRB-

MPR

demonstrate

infiltration

of

the

right

main

bronchus

from

a

heterogeneous

soft-tissue

massFig

MPR

shows

in

detail

the

extent

of

the

pneumomediastinum

with

associated

surgical

emphysema

and

right

pneumothorax

in

a

child

with

severe

combined

immune

deficiency

-LRB-

SCID

-RRB-

and

Pneumocystis

carinii

pneumoniaFig

MPR

in

lung

window

setting

demonstrates

left

lower

lobe

bronchiectasis

-LRB-

arrow

-RRB-

in

a

boy

with

a

history

of

chronic

aspiration

imaging

This

is

a

diagnostic

tool

only

in

certain

cases

as

it

usually

requires

more

time

and

postprocessing

skills

to

provide

information

already

included

and

demonstrated

in

the

axial

images

and

the

MPRs

There

is

no

doubt

however

that

the

reformatted

images

may

further

increase

the

diagnostic

confidence

which

eventually

affects

patient

management

particularly

pertinent

in

presurgical

assessment

Communication

with

the

referring

clinicians

is

simplified

as

the

images

portray

the

spatial

relationships

of

important

anatomical

structures

shaded-surface

display

techniques

These

are

only

applied

in

the

imaging

of

the

central

airways

and

they

are

usually

more

visually

impressive

than

clinically

useful

Their

generation

from

original

data

is

time-consuming

and

they

carry

the

risk

of

loss

of

density

information

due

to

problems

with

thresholding

Multiplanar

volume

reconstructions

These

are

selective

images

that

resemble

the

MPRs

and

depict

peripheral

airways

better

than

individual

sections

With

this

technique

a

combination

of

the

spatial

resolution

of

thin

sections

and

the

anatomical

display

of

thicker

slices

is

achieved

and

all

the

information

acquired

in

the

raw

data

set

is

used

The

routine

CT

images

are

combined

in

multiples

to

create

an

image

thicker

in

voxels

the

volume

slab

which

constitutes

an

interactive

sum

of

axial

coronal

and

sagittal

reconstructed

sections

-LSB-

-RSB-

By

using

different

algorithms

and

setting

thresholds

maximum

or

minimum

intensity

voxels

can

be

highlighted

within

the

slab

For

the

evaluation

of

the

airways

minimum

intensity

projections

within

the

slab

are

usually

applied

-LRB-

Fig.

-RRB-

-LSB-

-RSB-

Slabs

are

useful

in

detecting

and

localizing

micronodular

or

microtubular

patterns

and

in

analyzing

mild

forms

of

uneven

attenuation

of

the

lungs

-LSB-

-RSB-

However

they

are

time-consuming

and

should

be

reserved

for

cases

of

complex

morphology

to

give

the

clinicians

a

comprehensive

multilevel

roadmap

image

Fig.

vascular

ring

around

the

trachea

and

the

oesophagus

formed

by

a

double

aortic

arch

a

Diagrammatic

representation

of

the

abnormality

b

Corresponding

contrast-enhanced

axial

image

at

the

level

of

the

double

aortic

arch

the

right

part

being

the

dominant

c

VR

image

of

the

double

aortic

arch

from

a

left

anterior

oblique

view

Volume

slab

-LRB-

d

-RRB-

and

coronal

MPR

-LRB-

e

-RRB-

additionally

demonstrate

the

resulting

significant

narrowing

of

the

trachea

volume

rendering

These

represent

the

main

technique

for

reformatting

of

the

airways

and

the

vascular

structures

of

the

mediastinum

The

VR

technique

is

particularly

useful

for

displaying

structures

that

course

parallel

or

oblique

to

the

transverse

plane

and

those

that

develop

or

extend

into

multiple

planes

-LSB-

-RSB-

However

preliminary

editing

is

still

necessary

and

can

be

time

consuming

altering

work

patterns

in

CT.

In

VR

different

anatomical

tissues

are

represented

by

proportional

values

that

are

assigned

to

every

voxel

and

depend

on

the

range

of

tissue

attenuation

values

in

the

original

data

set

Voxels

are

selected

by

the

probability

of

belonging

to

the

object

of

interest

thus

they

are

displayed

in

different

colours

or

several

shades

of

grey

different

transparency

or

opacity

Transition

from

the

reconstructed

surface

to

the

surrounding

media

is

gradual

and

the

depiction

of

interfaces

like

the

inner

tracheal

lining

is

supposed

to

approach

their

true

appearances

Although

this

segmentation

technique

is

better

and

more

complicated

than

the

others

previously

mentioned

some

information

is

lost

during

processing

so

that

the

axial

images

are

still

indispensable

for

the

radiologist

to

assess

extraluminal

disease

and

identify

artefacts

Three-dimensional

VR-reconstructed

images

are

attractive

and

appealing

to

the

clinicians

as

they

may

better

illustrate

short

focal

areas

of

narrowing

the

craniocaudal

length

of

a

tracheobronchial

stenosis

and

complex

congenital

cardiovascular

and

tracheobronchial

anomalies

-LRB-

Figs.

-RRB-

Fig.

Contrast

enhanced

MCDT

-LRB-

collimation

-RRB-

showing

marked

tracheal

narrowing

and

an

aberrant

origin

of

the

left

pulmonary

artery

from

the

right

pulmonary

artery

-LRB-

pulmonary

sling

-RRB-

b

VR

demonstrating

an

elongated

and

stenotic

trachea

with

identification

of

a

separate

bronchus

for

the

right

upper

lobe

Virtual

bronchoscopy

The

inner

surface

of

the

air-containing

tracheobronchial

tree

can

be

displayed

with

virtual

bronchoscopy

-LRB-

VB

-RRB-

which

is

performed

with

either

polygonal

SSD

or

direct

VR

VB

is

a

noninvasive

and

accurate

technique

that

can

provide

bronchoscopic

views

of

the

central

and

the

peripheral

airways

-LRB-

Figs.

and

-RRB-

This

technique

like

fibreoptic

bronchoscopy

is

considered

supplementary

to

CT

and

referral

to

the

axial

sections

is

again

valuable

in

recognizing

artefacts

and

in

gaining

perception

of

orientation

within

the

virtual

airways

VB

uses

perspective

surface

rendering

which

takes

advantage

of

the

natural

contrast

between

the

airway

and

the

surrounding

tissues

-LSB-

-RSB-

The

point

for

viewing

is

located

intraluminally

so

that

external

structures

do

not

overlap

and

editing

takes

shorter

time

periods

Sub-millimetre

-LRB-

mm

-RRB-

slice

thickness

allows

deeper

penetration

and

visualization

of

the

bronchial

surface

down

to

bronchial

diameters

of

less

than

mm

it

is

however

associated

with

an

inevitable

increase

in

radiation

dose

-LSB-

-RSB-

Fig.

bronchus

a

Bronchography

and

b

volume

rendered

VB

demonstrating

an

accessory

bronchus

-LRB-

curved

arrows

-RRB-

On

the

MDCT

image

at

the

level

of

the

carina

a

more

cephalad

origin

of

the

apical

accessory

bronchus

isnoted

Again

VB

practically

never

really

adds

anything

new

to

the

established

diagnosis

However

pulmonologists

may

prefer

and

relate

to

these

images

in

conjunction

with

the

axial

or

the

reformatted

ones

-LSB-

-RSB-

In

practice

VB

is

of

limited

value

reserved

for

cases

where

bronchoscopy

is

not

applicable

-LRB-

children

in

whom

traditional

bronchoscopy

presents

a

risk

-RRB-

or

precise

navigation

is

not

possible

to

guide

airway

interventional

procedures

and

in

emergencies

such

as

infant

airway

-LRB-

tracheal

-RRB-

stenosis

which

can

not

be

otherwise

evaluated

-LSB-

-RSB-

The

images

produced

resemble

the

actual

bronchoscopic

ones

and

can

additionally

advance

distal

to

an

airway

obstruction

where

the

real

endoscope

can

not

penetrate

-LSB-

-RSB-

However

when

compared

to

fibreoptic

bronchoscopy

VB

does

not

allow

any

therapeutic

manoeuvring

is

incapable

of

detecting

endoluminal

lesions

smaller

than

mm

that

may

go

undetected

due

to

the

partial

volume

effect

and

provides

limited

information

about

mucosal

detail

-LRB-

morphology

vascularity

and

colour

-RRB-

making

differentiation

between

pathological

processes

and

retained

secretions

difficult

-LSB-

-RSB-

There

is

consensus

that

measurements

should

be

performed

only

on

sections

as

they

may

otherwise

be

inaccurate

-LSB-

-RSB-

The

technique

is

additionally

affected

by

the

partial

volume

effect

which

may

lead

to

misinterpretation

of

severe

stenoses

as

occlusions

and

the

threshold

level

is

therefore

of

importance

for

displaying

accurate

simulations

-LSB-

-RSB-

Dynamic

and

functional

inspiratory

and

expiratory

scanning

In

conjunction

with

single-breath-hold

MDCT

dynamic

and

functional

inspiratory

and

expiratory

scanning

helps

identify

strictures

areas

of

air-trapping

and

tracheobronchomalacia

but

is

rarely

applied

in

paediatric

practice

because

of

the

associated

radiation

burden

-LSB-

-RSB-

Peripheral

airways

Modern

volumetric

techniques

have

partially

overcome

the

difficulty

in

demonstrating

images

of

the

peripheral

airways

Data

are

acquired

and

reconstructed

at

a

later

time

allowing

thin-slice

high-resolution

images

at

any

level

so

that

a

whole

affected

bronchiectatic

segment

can

be

displayed

on

a

single

MPR/VR

oblique

section

-LRB-

Fig.

-RRB-

with

images

that

resemble

conventional

bronchography

and

may

influence

the

approach

for

tissue

sampling

-LSB-

-RSB-

If

there

is

suspicion

of

small-airways

disease

some

additional

expiratory

slices

may

be

useful

Whatever

the

application

we

perform

all

the

techniques

are

considered

as

an

adjunct

to

conventional

HRCT

evaluation

of

the

peripheral

airways

that

allows

accurate

and

precise

assessment

of

diffuse

lung

disease

at

very

low

doses

equivalent

to

approximately

ten

chest

radiographs

-LSB-

-RSB-

Clinical

applications

of

volumetric

imaging

of

the

airways

in

children

Selection

of

the

most

appropriate

CT

protocol

for

each

individual

case

is

paramount

in

imaging

of

the

airways

in

children

Ultimately

the

best

protocol

is

the

one

that

provides

the

most

relevant

information

at

the

lowest

radiation

burden

possible

The

indications

include

-LRB-

-RRB-

congenital

bronchial

anomalies

-LRB-

e.g.

accessory

bronchi

bronchial

hypoplasia

and

atresia

and

bronchopulmonary

foregut

malformations

-RRB-

-LRB-

-RRB-

tracheomalacia

-LRB-

-RRB-

tracheobronchial

strictures

-LRB-

congenital

and

acquired

-RRB-

or

tumours

and

-LRB-

-RRB-

peripheral

-LRB-

small

-RRB-

airways

disease

Tracheobronchial

anomalies

Approximately

of

adult

patients

who

undergo

bronchoscopy

demonstrate

some

form

of

congenital

variant

-LSB-

-RSB-

Tracheobronchial

anomalies

may

be

associated

with

recurrent

episodes

of

pulmonary

infection

and

airway

obstruction

and

usually

go

undiagnosed

with

conventional

imaging

-LSB-

-RSB-

Tracheal

bronchus

Tracheal

bronchus

with

an

incidence

of

represents

an

aberrant

bronchus

that

usually

arises

from

the

right

tracheal

wall

above

the

carina

and

ventilates

the

apical

segment

of

the

upper

lobe

-LRB-

Fig.

-RRB-

-LSB-

-RSB-

If

the

right

upper-lobe

bronchus

has

a

normal

trifurcation

then

the

tracheal

bronchus

is

supernumerary

and

may

end

blindly

it

is

also

called

a

tracheal

diverticulum

Left

tracheal

bronchus

has

also

been

reported

-LSB-

-RSB-

Its

presence

may

be

associated

in

some

patients

with

other

abnormalities

of

the

lung

or

within

the

spectrum

of

the

VACTREL

-LRB-

V

vertebral

A

anorectal

atresia

C

cardiac

T

tracheobronchial

R

renal

E

esophageal

L

lumbosacral/limb

abnormalities

-RRB-

association

Diagnosis

of

tracheal

bronchus

should

be

considered

early

in

the

clinical

course

of

intubated

patients

with

recurrent

right

upper-lobe

complications

-LSB-

-RSB-

Coronal

MPRs

are

particularly

helpful

in

demonstrating

the

presence

of

a

tracheal

bronchus

which

may

go

undetected

on

axial

images

Findings

can

be

additionally

supported

with

VB

Bronchial

atresia

Bronchial

atresia

may

present

with

a

variety

of

findings

depending

on

the

child

's

age

-LRB-

water-density

mass

in

newborns

bronchocele

and

air-trapping

during

childhood

and

solitary

pulmonary

nodule

or

area

of

emphysema

in

adults

-RRB-

In

doubtful

cases

MPRs

help

identify

mucoid

impaction

and

bronchocele

as

a

branching

structure

radiating

from

the

hilum

-LSB-

-RSB-

Bronchopulmonary

foregut

malformations

These

are

anomalies

of

pulmonary

development

that

are

due

to

abnormal

budding

of

the

embryonic

foregut

and

tracheobronchial

tree

They

include

duplication

cysts

characterized

by

an

isolated

portion

of

lung

tissue

communicating

with

the

upper

gastrointestinal

tract

or

the

central

nervous

system

such

as

bronchogenic

cysts

enteric

cysts

and

neurenteric

cysts

Symptoms

are

usually

provoked

by

the

size

and

location

of

the

cysts

which

may

cause

compression

of

the

trachea

or

bronchi

leading

to

distal

collapse

and

air

trapping

Infection

is

less

commonly

encountered

Pulmonary

underdevelopment

The

spectrum

of

pulmonary

underdevelopment

includes

agenesis

of

the

bronchus

and

lung

-LRB-

pulmonary

agenesis

-RRB-

presence

of

a

rudimentary

blind-ending

bronchus

without

lung

tissue

-LRB-

pulmonary

aplasia

-RRB-

and

bronchial

hypoplasia

with

reduction

of

lung

tissue

of

variable

degree

-LRB-

pulmonary

hypoplasia

-RRB-

-LRB-

Fig.

-RRB-

-LSB-

-RSB-

Scimitar

syndrome

The

scimitar

syndrome

also

called

venolobar

syndrome

and

hypogenetic

lung

syndrome

is

a

rare

congenital

cardiovascular

anomaly

involving

the

right

lung

It

consists

of

ipsilateral

anomalous

pulmonary

drainage

of

part

of

the

right

lung

into

the

inferior

vena

cava

hypoplasia

of

the

right

lung

dextrorotation

of

the

heart

hypoplasia

of

the

right

pulmonary

artery

and

anomalous

systemic

arterial

supply

to

the

lower

lobe

of

the

right

lung

from

the

subdiaphragmatic

aorta

or

its

main

branches

It

may

be

associated

with

abnormal

bronchial

anatomy

abnormal

diaphragm

hemivertebrae

and

anomalies

of

the

genitourinary

tract

CT

with

MPRs

shows

the

size

of

the

right

hemithorax

the

associated

bronchial

anomalies

and

the

anomalous

pulmonary

-LRB-

scimitar

-RRB-

vein

-LSB-

-RSB-

Sequestration

spectrum

The

sequestration

spectrum

includes

congenital

pulmonary

airway

malformations

-LRB-

CPAMs

-RRB-

anomalies

previously

termed

congenital

cystic

adenomatoid

malformations

the

pulmonary

sequestrations

and

also

hybrid

lesions

that

histologically

consist

of

both

entities

-LRB-

Figs.

and

-RRB-

CT

defines

their

location

extent

and

anatomical

relationships

and

evaluates

their

density

MPRs

and

VRs

can

impressively

demonstrate

the

arterial

feeder

from

a

subphrenic

aortic

branch

and

detect

the

venous

drainage

into

the

systemic

or

pulmonary

circulation

for

the

extra

and

intralobar

sequestrations

respectively

-LRB-

Fig.

-RRB-

Enhancement

of

the

cystic

wall

implies

infection

Tracheomalacia

Tracheomalacia

is

a

condition

that

refers

to

softening

of

the

tracheal

wall

This

is

caused

from

an

abnormality

of

the

cartilaginous

ring

and

hypotonia

of

the

myoelastic

elements

There

is

dynamic

collapse

of

the

trachea

during

expiration

which

leads

to

airway

obstruction

with

development

of

wheeze

cough

stridor

dyspnoea

cyanosis

and

recurrent

respiratory

infections

Primary

tracheomalacia

is

thought

to

be

caused

by

congenital

immaturity

of

the

tracheal

cartilage

and

may

be

associated

with

other

developmental

defects

such

as

a

vascular

ring/compression

or

tracheo-oesophageal

fistula

The

natural

history

shows

that

it

improves

by

the

end

of

the

first

year

In

secondary

tracheomalacia

previously

normal

cartilage

undergoes

degeneration

-LSB-

-RSB-

Tracheobronchial

strictures

Congenital

tracheal

stenosis

Congenital

tracheal

stenosis

is

a

rare

disorder

characterized

by

a

fixed

tracheal

narrowing

caused

by

complete

tracheal

cartilage

rings

-LRB-

Fig.

-RRB-

Approximately

of

congenital

tracheal

stenoses

are

focal

located

usually

in

the

lower

third

of

the

trachea

are

generalized

and

are

funnel-shaped

-LSB-

-RSB-

The

bronchi

are

usually

of

normal

size

This

abnormality

which

may

be

associated

with

other

anomalies

more

commonly

pulmonary

artery

sling

should

be

suspected

when

a

distal

tracheal

stenosis

is

recognized

in

an

infant

-LSB-

-RSB-

Congenital

lobar

emphysema/overinflation

Areas

of

malacia

or

stenosis

of

the

bronchial

cartilage

are

thought

to

be

the

aetiological

factors

in

the

development

of

congenital

lobar

emphysema/overinflation

through

a

check-valve

mechanism

which

is

characterized

by

progressive

distension/hyperinflation

of

a

lobe

most

commonly

the

left

upper

lobe

CT

will

typically

show

hyperinflation

of

the

affected

lobe

without

destruction

of

the

alveolar

walls

and

will

help

to

differentiate

this

condition

from

others

-LRB-

Fig.

-RRB-

Fig.

CT

of

an

infant

with

mediastinal

shift

shown

on

a

chest

radiograph

showing

hyperinflation

of

the

left

upper

lobe

without

destruction

of

the

alveolar

walls

consistent

with

congenital

lobar

emphysema

Acquired

tracheobronchial

stenoses

Acquired

tracheobronchial

stenoses

may

result

from

prolonged

intubation

-LRB-

post-intubation

webs

-RRB-

or

at

the

anastomosis

sites

following

surgical

intervention/lung

transplantation

In

patients

in

whom

the

axis

of

the

stenosis

is

vertical

or

slightly

oblique

it

is

usually

difficult

to

perceive

on

the

axial

images

alone

and

MPRs/VRs

are

useful

adjunctive

tools

-LRB-

Fig.

-RRB-

Compression

of

the

airways

of

cardiovascular

origin

This

is

a

relatively

common

complication

of

cardiovascular

diseases

that

may

go

unrecognized

for

some

time

Compression

is

caused

either

because

of

an

underlying

anomalous

anatomical

relationship

between

the

tracheobronchial

tree

and

the

vascular

structures

e.g.

a

double

aortic

arch

or

is

extrinsic

caused

by

enlarged

cardiac

or

pulmonary

vascular

structures

e.g.

congenital

heart

disease

dilated

pulmonary

arteries

-LRB-

Fig.

-RRB-

In

children

with

unexplained

respiratory

distress

stridor

wheezing

dysphagia

and

apnoea

a

high

index

of

suspicion

is

required

to

identify

these

lesions

that

cause

mechanical

airway

compression

-LSB-

-RSB-

A

vascular

ring

is

an

aortic

arch

anomaly

in

which

the

trachea

and

the

oesophagus

are

completely

surrounded

by

vascular

structures

They

are

formed

because

components

of

the

aortic

arch

complex

persist

or

regress

abnormally

If

the

airway

is

incompletely

encircled

then

a

vascular

sling

is

produced

-LSB-

-RSB-

The

most

common

and

clinically

serious

type

of

vascular

ring

is

the

double

aortic

arch

which

represents

a

persistence

of

both

right

and

left

embryonic

fourth

arches

joining

the

aortic

portion

of

the

truncoaortic

sac

to

their

respective

dorsal

aortae

-LSB-

-RSB-

It

typically

consists

of

a

right

and

a

left

arch

that

encircle

the

trachea

and

oesophagus

in

a

tight

ring

joining

distally

to

form

a

common

descending

aorta

-LRB-

Fig.

-RRB-

Variations

of

this

anomaly

have

been

reported

e.g.

hypoplasia

of

one

arch

-LSB-

-RSB-

Another

vascular

sling

can

be

produced

by

an

abnormal

origin

of

the

left

pulmonary

artery

from

the

right

pulmonary

artery

-LRB-

Fig.

-RRB-

As

the

former

crosses

to

the

left

it

encircles

and

compresses

the

right

main

bronchus

and

the

trachea

and

occasionally

the

left

main

bronchus

This

condition

is

usually

associated

with

other

congenital

anomalies

-LSB-

-RSB-

Foreign

body

aspiration

This

is

one

of

the

most

common

and

potentially

life

threatening

events

in

children

accounting

for

of

lethal

accidents

in

infants

aged

years

-LSB-

-RSB-

MDCT

of

the

chest

for

the

detection

of

radiolucent

foreign

bodies

is

not

the

investigation

of

first

choice

and

not

routinely

used

unless

a

pulmonary

infiltrate

that

fails

to

resolve

within

the

normal

recovery

period

of

days

is

present

-LSB-

-RSB-

It

is

vital

to

remember

that

actual

bronchoscopy

should

be

performed

even

in

cases

of

low

clinical

suspicion

and

no

direct

history

since

the

risk

of

overlooking

foreign

body

aspiration

may

be

lethal

and

may

cause

long-term

pulmonary

damage

Local

extension

of

neoplasms

MPRs/VRs

with

coevaluation

of

the

axial

images

are

the

method

of

choice

for

staging

of

hilar

or

mediastinal

neoplasms

They

demonstrate

interfaces

accurately

e.g.

the

relationship

of

the

lesions

to

the

bronchovascular

walls

and

the

presence

of

mediastinal

lymph

nodes

since

they

maintain

voxel

density

values

-LRB-

Figs.

and

-RRB-

More

complex

rendering

techniques

are

not

usually

required

-LSB-

-RSB-

Peribronchial

air

collections

MPRs/VRs

are

helpful

in

demonstrating

small

extraluminal

air

collections

and

leakages

of

surgical

anastomoses

especially

in

orthotopic

lung

or

heart/lung

transplant

patients

-LRB-

Fig.

-RRB-

They

can

impressively

show

fistulous

paths

that

may

be

indiscernible

on

axial

images

and

affect

patient

management

-LSB-

-RSB-

Additionally

by

correlating

with

VB

the

precise

location

of

the

leak

can

be

traced

prior

to

actual

bronchoscopy

Peripheral

airways

MPRs/VRs

using

MDCT

technology

have

achieved

more

accurate

visualization

of

the

distal

airways

The

VR

technique

is

applied

in

thin

overlapping

transverse

reconstructed

sections

using

a

high-resolution

algorithm

This

is

particularly

helpful

in

the

search

for

bronchiectasis

where

a

single

oblique

MPR/VR

section

may

include

the

whole

portion

of

the

affected

bronchi

-LRB-

Fig.

-RRB-

Additionally

when

planning

the

best

approach

for

tissue

sampling

the

relation

between

peripheral

nodules

and

the

afferent

bronchus

is

better

appreciated

using

the

MIP/VR

sections

Although

the

applications

of

conventional

HRCT

for

the

evaluation

of

the

peripheral

airways

are

beyond

the

scope

of

this

review

article

the

value

of

HRCT

should

not

be

overlooked

When

performed

individually

HRCT

is

considerably

less

of

a

radiation

burden

than

MDCT

-LRB-

Table

-RRB-

but

with

the

standard

HRCT

protocol

limited

slices

are

performed

and

the

imaging

of

the

mediastinum

is

insufficient

On

the

contrary

the

Combiscan

MDCT

protocol

with

the

possibility

of

HR

reconstructions

allows

detailed

parenchymal

evaluation

of

the

whole

of

the

chest

and

simultaneous

imaging

of

the

mediastinum

however

there

is

the

disadvantage

of

extra

radiation

burden

-LRB-

Table

-RRB-

Conclusion

MDCT

with

and

reconstructed

imaging

has

enhanced

the

applications

of

CT

in

imaging

of

the

chest

in

children

Obtaining

high-quality

scans

should

always

be

attempted

at

the

lowest

radiation

dose

possible

CT

and

bronchoscopy

are

supplementary

examinations

in

the

diagnostic

work-up

of

children

with

tracheobronchial

pathology

Although

and

rendering

techniques

are

not

the

first-line

diagnostic

tools

they

significantly

reinforce

the

confidence

in

a

diagnosis

even

in

complex

cases

In

specific

scenarios

they

may

supply

information

that

is

more

easily

interpreted

among

the

different

specialties

than

conventional

axial

scans

In

the

future

virtual

tracheobronchial

endoscopy

is

anticipated

to

be

applied

for

interactive

virtual-reality

guidance

in

surgical

procedures

of

the

airways

O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O B O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O

volumetric
tracheobronchial tree
children