Chest Imaging

Imaging protocols for CT chest: A

recommendation
Ashu Seith Bhalla, Abanti Das1, Priyanka Naranje, Aparna Irodi2, Vimal Raj3, Ankur Goyal
Department of Radiodiagnosis, All India Institute of Medical Sciences, 1Department of Radiodiagnosis, Safdarjung Hospital and
Vardhaman Mahavir Medical College, 2Department of Radiology, Christian Medical College and Hospital, Vellore, Tamil Nadu,
3
Department of Radiology, Narayana Institute of Cardiac Sciences, 258A, Hosur Rd, Bommasandra Industrial Area, Bengaluru,
Karnataka, India

Correspondence: Dr. Ashu Seith Bhalla, Department of Radiodiagnosis, All India Institute of Medical Sciences, New Delhi ‑110 029, India.
E‑mail: ashubhalla1@yahoo.com

Abstract
Computed Tomography (CT) is the mainstay of diagnostic imaging evaluation of thoracic disorders. However, there are a number of
CT protocols ranging from a simple non‑contrast CT at one end of the spectrum, and CT perfusion as a complex protocol available
only on high‑end scanners.With the growing diversity, there is a pressing need for radiologists, and clinicians to have a basic
understanding of the recommended CT examinations for individual indications. This brief review aims to summarise the currently
prevalent CT examination protocols, including their recommended indications, as well as technical specifications for performing them.

Keywords: Computed tomography angiography; computed tomography chest; computed tomography contrast; dual energy
computed tomography; low‑dose computed tomography; protocol; pulmonary embolism

Introduction balance between attaining adequate diagnostic information

and patient safety needs to be kept in perspective. In
Computed Tomography (CT) forms the workhorse another clinical scenario, where patients may move across
of imaging evaluation of thoracic diseases. With the institutions or hospitals for treatment, with the availability
ever‑expanding clinical spectrum of thoracic disorders, of standardised imaging protocols, there should be no
and diseases with thoracic manifestations, there has been need for repeat imaging as recurrent imaging would entail
increasing frequency of chest CT being ordered. Hence, additional radiation burden and contrast administration.
there is a growing need for the radiologist, and the referring
clinician to have a basic understanding of the recommended Although ultrasound and magnetic resonance imaging
CT examination for specific individual indications. (MRI) are also being increasingly used in the evaluation of
the chest, this review however, confines itself to CT. This
The attendant concern of increased radiation exposure, review article aims to summarize the recommended thoracic
especially in young individuals, as well as the use of iodinated CT protocols for various clinical/radiological indications
intravenous contrast material in contrast‑enhanced CT including their technical parameters as well as applications
should be kept in mind while ordering such investigations,
more so, in patients who require repeated imaging. Hence, a This is an open access journal, and articles are distributed under the terms of
the Creative Commons Attribution‑NonCommercial‑ShareAlike 4.0 License,
Video Available on: www.ijri.org which allows others to remix, tweak, and build upon the work non‑commercially,
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Access this article online the identical terms.
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Cite this article as: Bhalla AS, Das A, Naranje P, Irodi A, Raj V, Goyal A.
Imaging protocols for CT chest: A recommendation. Indian J Radiol Imaging
DOI: 2019;29:236-46.
10.4103/ijri.IJRI_34_19
Received: 15-Jan-2019 Revision: 06-Mar-2019
Accepted: 21-Mar-2019 Published: 30-Oct-2019

236 © 2019 Indian Journal of Radiology and Imaging | Published by Wolters Kluwer ‑ Medknow
 Bhalla, et al.: Recommendations for imaging protocols for CT chest

of newer advancements in day‑to‑day clinical scenario (PUO).Hence, the use of the term clinico‑radiographic
based on current literature. The review does not address the indications is apt.
status of ECG‑gated cardiac/aortic CT. This manuscript was
prepared as a part of initiative of Indian College of Radiology Broadly, the protocols may be divided into non‑contrast CT
and Imaging (ICRI) to standardise imaging protocols in (NCCT), contrast‑enhanced CT (CECT) and then multiple
chest imaging. modifications are available within this basic framework
[Table 1]. Table 2 details the choice of CT protocol based on
Protocols vs Clinico‑Radiographic Indications the clinico‑radiographic indications.There are certain aspects
of CT acquisition, though, which are common amongst all
The indication to perform a chest CT can be clinical, or the protocols. Currently, all thoracic CT scans should be
based on an abnormality on prior imaging studies such acquired in volumetric mode in full inspiration. Sequential
as chest radiograph (CXR), fluoroscopy, MRI or abdomen mode may be used while acquiring limited expiratory scans.
CT. In almost all clinical scenarios, chest radiograph Certain clinical situations mandate the use of intravenous
should be performed initially. Findings on CXR would (IV) contrast such as evaluation of pyrexia of unknown
help to tailor the appropriate CT examination. However, origin (PUO) or acute infections. Omission of contrast in
in several instances, CT will be performed even if the such scenarios can lead to inadequate evaluation of critical
chest radiograph is normal e.g. Pyrexia of unknown origin findings like mediastinal lymph nodes or complications.

Table 1: Types of Imaging protocols Non‑Contrast CT (NCCT) Chest Protocols

CT protocols
Non-contrast CT chest protocols Routine NCCT NCCT chest can be performed in various protocols such as
LDCT routine NCCT in standard dose, low dose CT (LDCT) or
Ultra ‑LDCT Ultra‑LDCT and their indications and technical parameters
Cine CT are summarized in Table 3.
Contrast-enhanced CT chest protocols Routine CECT
CT angiography protocols CTPA
Routine NCCT
CTA Frequent indications of NCCT chest are suspected cases or
Combined protocols follow up of metastasis, bronchiectasis, ILD and pulmonary
Split‑bolus protocol infections.
Triple rule out
For masses/nodules (Functional Imaging) Dynamic multiphasic CT
Perfusion CT
Image acquisition
NCCT ‑ Non‑contrast CT; LDCT ‑ low dose CT; CECT ‑ Contrast enhanced CT; CTPA ‑CT
All non‑contrast scans should be acquired in volumetric
pulmonary angiography; CTA ‑ CT angiography mode, scanning extending from thoracic inlet to caudally

Table 2: Choice of Chest CT protocol according to clinico‑radiographic scenario

Clinicoradiographic indications CT Protocol
Screening for pulmonary metastasis NCCT
As part of Lung Cancer Screening Program LDCT
Unexplained dyspnoea on exertion, suspected or known case of ILD (e.g. In connective NCCT
tissue diseases, rheumatological disorders), follow ‑up of ILD
Suspected or known bronchiectasis, small airway disease NCCT/LDCT
PUO CECT (chest and abdomen)
Non‑resolving pneumonia CECT
Mediastinal widening CECT
Malignant pleural effusion, empyema, chest wall disease CECT
Staging and follow‑up of lung cancer CECT, Biphasic protocols*
Staging and follow ‑up of lymphoma CECT (neck, chest and abdomen)
Unexplained vocal cord palsy CECT
Evaluation of solitary pulmonary nodules CECT, Dynamic multiphase CT
Blunt or penetrating chest trauma CECT, CTA
Recurrent/Significant haemoptysis CTA, Split‑bolus CTA
Atypical chest pain (additional diagnosis other than acute coronary syndrome is CTA
considered e.g., Pulmonary embolism or aortic dissection)
Intermediate to high clinical probability of pulmonary thromboembolism or positive CTPA
D‑dimer level including pregnant patients (ACR Appropriateness Criteria, revised 2016)
NCCT‑ refers to routine non contrast CT as detailed in the text; ILD‑ interstitial lung disease ;CECT ‑ Contrast enhanced CT; CTPA‑ CT pulmonary angiography; CTA ‑ CT angiography; *. Is used
when these are to be used in special situations detailed in text

Indian Journal of Radiology and Imaging / Volume 29 / Issue 3 / July - September 2019 237
 Bhalla, et al.: Recommendations for imaging protocols for CT chest

Table 3: NCCT chest protocols according to indications

Routine NCCT/standard dose CT Low-dose CT Ultra Low-Dose CT
Indications Suspected pulmonary metastases ILD evaluation* Lung cancer screening/nodule detection
ILD Lung cancer screening Screening lung as a part of coronary
Bronchiectasis Follow‑up imaging for nodules/pulmonary CTs.
Deranged renal parameters infections, bronchiectasis, ABPA, CF
Febrile neutropenia
Acquisition protocol
kVp 100 (<~80kg) 80‑120 120‑140
120 (~80‑113kg)
140 (>113kg)
mA 35 22 Without AEC
with AEC
Tube current (mAs) 130‑200 20‑40 Employs a fixed mAs value‑ 10
Collimation Lowest possible on the scanner (e.g. 0.6) Lowest possible on the scanner Lowest possible on the scanner
Pitch 1.2 Highest pitch NS
Rotation time 0.5 0.5 NS
Slice thickness 1.2‑1.5mm 1.2‑1.5mm NS
Matrix 512×512 512×512 512 × 512
Expected Radiation Dose 3‑8 mSv# 1‑3 mSv 0.182±0.028mSv
i.e. <1 mSv
*Use of LDCT in ILD is recent concept, explained in text.; ABPA‑ Allergic bronchopulmonary aspergillosis; CF‑ Cystic fibrosis; ILD ‑ interstitial lung diseases; NS‑ Non specified. #With modern
scanners and availability of iterative reconstructions, a radiation dose of 2‑3mSv is possible

include upper abdomen [Figure 1]. Patients are imaged in A B

supine position in suspended deep inspiration with arms
extended overhead to reduce beam hardening artefact.
Some modifications of the NCCT scans include expiratory
and prone scans.

Image reconstructions
The acquired CT images are reconstructed into soft tissue
mediastinal window (20‑30 kernel) and lung window C D
(in sharp algorithm, 60‑80 kernel) and in 1.2 ‑1.5 mm section
thickness for interpretations. The 60‑80 kernel reconstruction
becomes the high resolution CT and hence HRCT chest need
not be acquired in sequence mode separately as in earlier
times. Thus, non‑volumetric sequential mode HRCT has no
indication in current era and any volumetric CT chest data
can be reconstructed in high‑resolution algorithm. The classic
HRCT chest protocol was used in earlier times for acquiring Figure 1 (A-D): NCCT Chest (Routine): (A) Supine topogram image: the
red box shows the area of coverage for routine chest CT, extending from
high resolution images of lung parenchyma. The technique thoracic inlet to upper abdomen. Images reconstructed in soft kernel
includes using thin collimation, usually 1‑2 mm, which in standard lung b50s (B) and mediastinal windows b30s (C); and in
improves the spatial resolution and coupled with a high high‑resolution reconstruction algorithm b80s (D)
spatial frequency reconstruction algorithm which makes the
structure visibly sharper. The images are acquired at 10mm Expiratory scan
interval, thereby considerably reducing the radiation dose. In These scans are mainly acquired in cases of suspected
the centres where MDCT is not available, HRCT acquisition air‑trapping, small airway disease or tracheobronchomalacia,
is still used for evaluation of diffuse lung diseases. and may include contiguous acquisition similar to
the supine inspiratory scan, or a sequential three‑step
The volumetric data can be further subjected to various acquisition involving upper thoracic trachea, carina and
post‑processing on workstations such as multiplanar lung bases through the diaphragm [Figure 3]. Scans can
reconstructions (MPRs), maximum intensity projection be acquired as sequential step‑wise acquisition which
(MIP), minimum intensity projection (minIP), volume delivers less radiation and is preferred in young patients,
rendered images for virtual bronchography, and virtual while volumetric mode can be used in elderly patients.
bronchoscopy to evaluate airways [Figure 2]. Amongst Whenever there is appearance of ground glass opacities,
these, minIP should be performed whenever airways are mosaic pattern on routine NCCT or suspicion of an airway
to be evaluated, and MIP images for nodule identification. dominant disease, it is necessary to acquire an expiratory
238 Indian Journal of Radiology and Imaging / Volume 29 / Issue 3 / July - September 2019
 Bhalla, et al.: Recommendations for imaging protocols for CT chest

CT. In fact a further modification of this is the cine CT attempt to deliver reduced radiation dose to the patient
described subsequently in detail. while maintaining diagnostic quality images.[2] However,
several technical parameters relating to the scan acquisition
Prone scans needs to be modified to achieve optimal results. Usually,
Prone position is advised to differentiate between dependent low dose CT is performed using tube voltage of 120 kVp
density and features of early interstitial lung disease, when (KVp is adjusted according to patient’s weight) and tube
there is equivocal increase in attenuation and reticulation current ranging from 40‑80 mAs. Such low tube‑current
noted on dependent parts of bilateral lung parenchyma on generates increased image noise, which can be partially
routine supine scan [Figure 4]. The acquisition should be compensated by using iterative reconstruction algorithm
restricted to the area of interest. (now available with many CT manufacturers). However,
the vast majority of scanners in the world are still
Low‑dose CT (LDCT) without iterative reconstructions software and use images
LDCT protocols have been developed for patients requiring reconstructed using conventional filtered back‑projection
repeated imaging such as several patients with interstitial [Figure 5].
lung disease (ILD) or nodule. Hence, the need to adhere
to ALARA (As Low As Reasonably Achievable) principle Reconstructed slice thickness is kept at 2.5 mm or higher
cannot be over emphasized. Guidelines exist for dose (for non‑targeted FOV in low frequency algorithm) while a
optimization depending on indications. slice thickness of 1.0‑1.5 mm at high frequency algorithmic
reconstruction needs to be done through the region of interest
For nodule detection/Lung cancer screening (ROI) to improve spatial resolution. The ROI needs to be
Low‑dose protocol is recommended for pulmonary viewed in both low‑ and high‑spatial‑frequency algorithm
nodule follow‑up as well as screening for lung cancer in
select high‑risk patients.[1] Low‑dose CT refers to scanning
techniques which use tube current less than 100 mAs in an

A B

A B
Figure 3 (A and B): NCCT variants. (A) Inspiratory scan showing mild
mosaic attenuation (arrow). (B) Expiratory CT performed in low dose
C D
shows multiple areas of air trapping (black arrows). Note the bowing
of posterior walls of bronchi suggesting adequate expiratory phase
(white arrow)

A B

Figure 2 (A-D): Image reformatting: (A and B) Sagittal and coronal

reformation in standard lung window to allow three‑dimensional view.
(C) Axial maximum intensity projection (MIP) in lung window for
enhanced visualization of nodules. (D) Coronal minimum intensity
projection (minIP) in lung window for assessment of tracheobronchial
airway. (D) Virtual bronchography (volume rendered display) for
visualization of airways
C

Figure 5 (A-C): Low dose CT (LDCT) nodule follow-up. (A).LDCT

A B done in a 46-year old chronic smoker shows a nodule in left lower
Figure 4 (A and B): NCCT variants. NCCT chest in supine (A) position lobe (white arrow).(B) Follow-up LDCT done 6 months later shows no
shows ground glass opacities in posterior basal segments of bilateral interval change in size. (C) Axial maximum intensity projection (MIP)
lower lobes (arrows). CT performed in prone position (B) shows clearing image in lung window shows another smaller nodule (black arrow) in
of the GGOs suggestive of dependent densities (arrows) right lower lobe in addition to left lower lobe nodule

Indian Journal of Radiology and Imaging / Volume 29 / Issue 3 / July - September 2019 239
 Bhalla, et al.: Recommendations for imaging protocols for CT chest

as the latter reconstruction may erroneously show high (i.e. volumetric inspiratory) should be between 1 to 3 mSv
density edge artifacts simulating calcium. Recent evidence (low‑dose CT), with added caution to avoid ultra‑low dose
shows that there is no significant difference in inter‑observer CT (<1 mSv).[7]
and intra‑observer variability in measurement of nodule
volumes when low‑dose CT is compared to standard dose Ultra‑low dose CT
CT, suggesting that the former can be used for follow When doses are kept at <1 mSv, it is often referred to as
up of pulmonary nodules.[2‑5] Various studies have been ultra‑low dose CT. Its utility has been shown in screening
performed with different combinations of kVp and mAs in for lung cancer and in screening for lung nodules as
the context of low‑dose CT leading to variable estimated a part of coronary CT. [8] This is strictly restricted to
doses, but on an average an acceptable low‑dose CT screening/surveillance and not for routine clinical
screening can be performed with an approximate effective evaluation of lung parenchyma.
dose of 2mSv.[6]
Cine CT
For suspected ILD Cine CT is not available in every scanner, and if available
Use of low dose CT is a recent concept in imaging of ILD. An tailor coverage to airway (critical areas being lower trachea
attempt should be made henceforth to modify unstructured and carina). Cine CT without table feed during free
protocols and achieve dose <3 mSv even in ILD patients. breathing has been investigated as an alternative diagnostic
The current recommendations for performing CT for modality for assessment of dynamic airway collapsibility
imaging evaluation of suspected ILD includes volumetric and has been found to have comparable diagnostic efficacy
acquisition with sub‑millimetric collimation, highest pitch as flexible bronchoscopy, which is considered the gold
and shortest rotation time. Tube voltage and tube current standard for diagnosis[9‑11] [Figure 7]. In fact, the former is
are determined based on patient size. The recommended considered better than paired static inspiratory/expiratory
acquisitions include supine sustained end‑inspiratory images. Initial studies had used electron beam CT and single
phase (volumetric) and supine sustained end‑expiratory detector CT for cine acquisition of airway during functional
(volumetric or sequential) phase [Figure 6]. Additional manoeuvres and showed encouraging results, albeit with
optional scan includes prone inspiratory scan (volumetric limited z‑axis coverage and increased radiation dose.[12]
or sequential) limited to lower lobes. Image reconstruction Subsequently, 64‑slice MDCT with z‑axis coverage of more
is done at thin slices (1.5 mm) at high‑spatial‑frequency than 3 cm was successfully employed for dynamic airway
algorithm which can be contiguous or overlapping. assessment during coughing.[13] The anatomical coverage
Post‑processing tools including minIP and MIP to be used to was further extended to 16 cm using a 320‑row MDCT by
assess low attenuation lesions and micronodular infiltration, Wagnetz U et al. to cover the airway from lower end of larynx
respectively. The radiation dose for first acquisition to the origin of lower lobe bronchi.[14]

Recently, respiratory gated 4D CT of the whole chest has

been performed with a dose‑modulated protocol at a pitch
of 0.09 (lowest possible), minimal exposure parameters
(80 kVp and 10 reference mAs) and thin collimation (16 ×
1.2 mm). Image reconstruction was done using iterative
reconstruction algorithm, at slice thickness of 1.5mm at
increments of 1.0 mm in a medium soft kernel.[15] The
reported radiation dose ranged from 2.9 to 3.1 mGy
A B
CTDIvol. The radiology technicians should be aware of such
advanced protocols available in the scanners.

C D
Figure 6 (A-D):LDCT for evaluation of ILD. (A) Axial image of LDCT in
high resolution reconstruction algorithm in a 65‑year old chronic smoker
with suspected ILD. (B and C) Routine axial and coronal reconstruction A B
in lung window allow evaluation of cranio‑caudal and axial distribution of Figure 7 (A and B): Cine CT showing dynamic collapsibility of right
reticulations, interlobular septal thickening and macrocysts. (D) Curved main bronchus more than 50 percent suggestive of bronchomalacia.
MPR along the axis of bronchus (black arrow) allows distinction between (A) Saved screenshot of inspiratory phase. (B) Saved screenshot of
honeycombing or macrocysts and traction bronchiolectasis expiratory phase. (C)Video file (supplementary).

240 Indian Journal of Radiology and Imaging / Volume 29 / Issue 3 / July - September 2019
 Bhalla, et al.: Recommendations for imaging protocols for CT chest

Contrast Enhanced CT (CECT) Chest Protocols to the volume, rate and manner of contrast injection
(monophasic vs biphasic), timing of scan acquisition and
The numerous options of contrast enhanced scans range use of dual energy.
from a routine contrast enhanced CT (CECT) to CT
perfusion scans. Various contrast media are available for Protocols for primary visualisation of vascular tree (CT
use in contrast enhanced CTs. For routine CECT, iodine angiography protocols)
concentration of 300‑350 mgI/ml suffices whereas for Different CT angiography protocols are devised to account
CT angiography protocols, a higher concentration of for different time of peak opacification of the two vascular
350‑400 mgI/ml is preferred. The dose of contrast to be trees of chest, pulmonary and systemic (aortic) following IV
administered depends on the weight of the patient and contrast, with the former opacifiying 10‑14 seconds earlier.
current CT scanners allow 1‑1.5 ml/kg to be used for
routine CECT as well as CTA protocols. Doses up to 2 ml/kg CT Pulmonary angiography (CTPA)
may sometimes be employed for CTA protocols in obese CTPA is performed for suspected pulmonary embolism (PE),
patients. Availability of Dual energy CT scanners further follow up of PE and evaluation of cause of pulmonary artery
helps to reduce the contrast dose because of better contrast hypertension. CTPA should be performed during shallow
visualization at lower keV images. inspiratory breath hold; mainly to avoid Valsalva manoeuvre
associated with deep inspiration during the acquisition as
Routine CECT chest it can lead to poor vascular opacification due to dilution of
Routine CECT chest essentially retains the same parameters as contrast bolus with unopacified blood flowing from inferior
NCCT with administration of intravenous contrast. Usually a vena cava.[19] For very sick patients, or those who cannot
scan delay of 55‑70 seconds is kept following administration follow respiratory commands, CTPA can also be performed
of contrast to allow for optimal enhancement of soft tissues[16] with free‑breathing by increasing the pitch in dual‑source
[Figure 8]. Contrast is usually delivered using hand injection CT scanners (up to 3) so that the scan is complete in less than
with optional use of power injector and bolus chase. CECT a second.[20] The same when coupled with low‑voltage and
chest is often coupled with upper abdomen (liver and adrenals) iterative reconstruction algorithm can substantially reduce
for baseline staging and follow‑up of lung cancer, and with the radiation dose with acceptable image quality.[19]
abdomen and neck for PUO evaluation or other malignancies
such as lymphoma staging. Two different protocols exist for CTPA scans should be acquired in caudo‑cranial direction
the same: the first one involves single delayed acquisition of to avoid streak artefacts from dense contrast media in
chest and abdomen. The other one uses dual acquisition‑an superior vena cava or subclavian vein, thus allowing
earlier acquisition for chest (20‑35 seconds delay), and a time for the saline chaser to clear off the contrast to chest
second delayed acquisition for abdomen in portal venous by the time imaging proceeds to that level [Figure 9]. To
phase.Although, no consensus exists over the superiority of avoid these artefacts, some authors have also proposed a
one protocol over another, recent evidence suggests that a triphasic contrast injection protocol that allows for graded
single 60 seconds delayed scan covering chest and abdomen decrease in contrast concentration in a phasic manner i.e.,
offers better image quality in terms of improved lymph nodal Phase 1: 50 ml of undiluted contrast agent, phase 2: 30 ml
visualisation, reduced perivenous contrast‑ related artefacts, of contrast in 70%:30% dilution of saline and contrast,
lower radiation dose with acceptable thoracic vascular and and phase 3: 50 ml of pure saline).[20] A minimum mean
hepatic parenchymal enhancement.[17] Some authors also attenuation value of 250 HU is required in main pulmonary
suggest a modified contrast infusion protocol for better artery for accurate diagnosis of pulmonary embolism.[21]
visualisation and characterisation of a pleural disease with a
greater infusion rate (150 ml at 2.5 ml/sec).[18] With the advent of dual‑energy CT, there have been several
advancements in the technical aspect of image acquisition
The various modifications of contrast‑enhanced scans and post‑processing of CTPA. The most important
as discussed below and detailed in Table 4 are related advantages of image acquisition in dual energy mode are:
(1) generation of material density display which can be used
to generate iodine perfusion maps providing panoramic
visual assessment of lung parenchyma thereby, highlighting
any focal areas of perfusion defect, (2) generation of virtual
non‑contrast images, and (3) post‑processing for image
optimization (like low keV images can be used even if the
contrast opacification was not adequate due to an error in
A B C timing or calculating the dose of contrast bolus).[19] Several
studies have shown that a combination of high pitch
Figure 8 (A-C): (A-C) Contrast‑enhanced CT chest (Routine). Axial,
coronal and sagittal reformations in standard mediastinal window. The (using dual source scanner), low tube‑voltage acquisition
cross‑bar allows three‑dimensional localization of lesion with iterative reconstruction for post‑processing can not only
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 Bhalla, et al.: Recommendations for imaging protocols for CT chest

Table 4: Protocols of contrast enhanced scans for opacification of pulmonary and systemic circulation
CTPA (Pulmonary circulation) CTA (Systemic Circulation) Combined protocol‑ (Pulmonary +
systemic circulation)
Indication Pulmonary embolism Aorta and its branches Both pulmonary artery and aorta and its
branches.
Area of coverage Lung apex to level of diaphragm in all cases. Thoracic inlet to lower border Thoracic inlet to lower border of L2
Just above aortic arch to just below heart (in of L2
young or pregnant patients with normal CXR
and minimal suspicion of PE)
Slice thickness ≤2mm ≤1.5mm ≤1.5mm
For reconstruction
kVp For patients <30 years and 30‑60 years: 100kVp Dual energy (80kVp and 140kVp
120, 100 or 80 kVp depending on patient
BMI or automatic tube voltage selection
For patients >60 years: 120 kVp
mAs For patients <30 years: 150 mA with tube Automated tube current Automated tube current modulation
current modulation. modulation
For patients 30‑60 years and >60 years:
200 mA with tube current modulation.
Rate of contrast injection (where 3‑4ml/s (normal resting heart rate) 3.5‑4ml/sec 3/4th contrast at 5ml/s
applicable) 4‑5ml/s (elevated cardiac output) 1/4th contrast at 3ml/s
Saline chase at 3ml/s
ROI position (where applicable) Pulmonary trunk or MPA or right atrium Descending aorta Ascending aorta
Threshold HU (where applicable) 60‑100HU* 100HU 100HU
Time delay/phase of acquisition 4‑5 sec after bolus trigger time 6 sec after bolus trigger time 5 sec after bolus trigger time
Reconstruction Contiguous image reconstruction at Reconstruction interval 2.0mm Axial image reconstruction at 1.5 mm
intermediate‑spatial‑resolution algorithm. or similar depending upon slice thickness and increment of 1.2 mm
View in cine mode at window width scanner, at standard mediastinal at standard mediastinal and lung
450‑600HU and window level 35‑100HU (#) window (Window level 40HU, windows.
and maximum intensity projections (MIP) window width 400HU)
*60 HU is used by several dual source DECT scanners. #Pulmonary embolism can be missed when images with very bright contrast is viewed only on mediastinal window settings

In cases of chronic pulmonary thromboembolism (PTE),

the CT can be done in two phases (pulmonary and
systemic) when using dual energy CT. This helps to
generate iodine perfusion maps, to demonstrate the areas
of perfusion defects in pulmonary arterial phase, which
subsequently gets opacified in late (aortic) phase if sufficient
collateralisation has taken place[22] [Figure 10]. Even when
A B using single source MDCT scanners, biphasic protocol is
advocated for demonstration of systemic collaterals that
develop in chronic PTE.

CT Angiography for systemic arteries

The term CT angiography (CTA) is used when primarily
the focus is on systemic circulation (aorta and its branches)
[Figure 11]. CTA of thorax is essentially performed in three
scenarios 1. Evaluation of hemoptysis which includes
pre‑procedural imaging for bronchial artery embolization,
C D
2. Suspected aortic dissection/aneurysm, 3. Demonstration
Figure 9 (A-D): CT Pulmonary angiography (CTPA on a DECT
of anomalous artery in congenital lung malformations
scanner). (A) ROI positioning in right atrium. (B) Enhancement curve
for bolus tracking showing the beginning of acquisition at 60HU. Axial (e.g., sequestration). Among these, CTA for aortic
(C) and coronal (D) MIP images show the optimal visualisation of main dissection/aneurysm evaluation requires an ECG gated
pulmonary artery and peripheral branches acquisition, the complete discussion of which is beyond
the scope of this article.
significantly reduce patient dose with comparable image
quality, but can also achieve improved temporal resolution CT angiography for haemoptysis
(reducing motion artefacts and allowing simultaneous MDCT angiography of thorax is increasingly being
cardiovascular evaluation) with reduced contrast dose.[19] recommended in the diagnostic work‑up and management
242 Indian Journal of Radiology and Imaging / Volume 29 / Issue 3 / July - September 2019
 Bhalla, et al.: Recommendations for imaging protocols for CT chest

A B
A B

C D
Figure 11 (A-D): CT thoracic angiography ‑ CTA. (A) ROI
C D positioning in descending thoracic aorta with trigger at 100 HU. Axial
Figure 10 (A-D): Iodine map (DECT‑CTPA) in an 83‑year old female (B and C) and Coronal (D) reconstructed images show faint attenuation
with chronic pulmonary thromboembolism. (A and C) Axial and coronal of right sided heart and pulmonary arteries, with predominant
color‑coded iodine map overlay generated from pulmonary arterial opacification of left sided heart and aorta
phase shows multiple wedge‑shaped perfusion defects peripherally
in bilateral hemithorax. (B and D) Axial and coronal colour –coded generation of scanners, especially with the introduction
iodine map overlay of subsequently acquired aortic phase; shows
uniform distribution of iodine bilaterally suggestive of homogenous of dual energy CT. The authors have adopted a similar
arterial perfusion (through systemic collaterals), filling previous areas biphasic contrast‑injection protocol (split‑bolus) with added
of pulmonary perfusion defects modifications, which is currently being followed at our
institute for evaluation of haemoptysis and is described
of hemoptysis, especially for planning of bronchial in Table 4. The scan thus acquired allows evaluation of
artery embolization (BAE). [23] Antoine Khalil et al. [24]
bronchial arteries (branches of thoracic aorta), non‑bronchial
described an angiographic protocol on 16‑slice scanner
systemic supply as well as the pulmonary vessels, in a
(120kV and 180 mA) which involved cranio‑caudal scan
single acquisition with smaller contrast dose.[28] The benefit
acquisition from lung apices to lung bases in supine position
of opacification of pulmonary vessels is that in addition to
and maximum inspiratory breath hold. However, a more
detecting the pulmonary arterial causes of haemoptysis
extensive coverage from the base of the neck till the level
(like pseudoaneurysms), the dilated pulmonary arterial or
of renal arteries is recommended, corresponding to L2
venous branches (corresponding to areas of shunting) can
vertebral level to include non‑bronchial systemic supply
also be well seen, aiding in exact localization of bleeding
from branches of arch of aorta and infra‑diaphragmatic
[Figure 12].
arteries.[25] The protocol is described in Table 4.

Triple rule out CT (TRO CT)

Combined protocols (For pulmonary and systemic circulation)
There is a growing trend towards achieving adequate TRO CT is a dedicated ECG gated examination aimed to
opacification of both aortic and pulmonary systems in a evaluate aorta, coronary artery and pulmonary artery and
single acquisition to allow simultaneous evaluation without mid‑to lower thorax in a single scan. TRO is essentially used
additional exposure of multiple scans. This is primarily to rule out acute coronary syndrome (ACS), pulmonary
achieved by using split‑bolus techniques for contrast embolism or acute aortic syndrome as the underlying
administration or prolonged administration of contrast. cause for patients presenting with chest pain to emergency
department (low‑to moderate risk of ACS or non‑ACS
Split‑bolus protocol for hemoptysis diagnosis considered).[29] The scanning length approximates
A comprehensive evaluation into the source of hemoptysis 20 cm extending from above aortic arch till the caudal aspect
requires optimal enhancement of both bronchial (systemic) of heart, and is acquired in less than 15 second under ECG
and pulmonary arterial bed in a single examination.[26] Hence, gating. Scan parameters include tube voltage of 120kVp,
CT using biphasic contrast bolus injection is advocated mean effective tube current 600mAs per section with mean
for optimal visualization of both pulmonary arteries and effective radiation dose in helical mode of scanning of
thoracic aorta without additional radiation or contrast 18mSv without tube current modulation and 8.75 mSv with
compared to monophasic contrast injection.[27] Although the modulation. There is extensive literature available on ECG
earlier protocols used higher doses of undiluted contrast, the gated triple rule‑out CT, the details of which are beyond
contrast dose has significantly come down with the current the scope of this article.

Indian Journal of Radiology and Imaging / Volume 29 / Issue 3 / July - September 2019 243
 Bhalla, et al.: Recommendations for imaging protocols for CT chest

Protocols for multiphasic evaluation of masses/nodules on enhancement characteristics[31] [Figure 13]. A similar
(functional imaging) protocol has recently been adopted in SPUtnIK trial for
Different tumours opacify at different timings following characterization of incidental indeterminate solitary
IV contrast injection based on the tumour histology and pulmonary nodules (SPN).[32] This mode of CT acquisition
amount of angiogenesis. A single phase CT may hence can be performed even on low‑end scanners and the detector
fail to demonstrate the tumour and its extensions reliably. collimation varies accordingly. The suitability of the nodule
Also, nodules demonstrate different peak enhancement at for multiphase CT is initially assessed prior to performing
different times depending on aetiology. Similarly, a biphasic multiphase CT. Hence, a baseline routine NCCT/LDCT is
acquisition in two phases maybe required if all arterial and performed to confirm the size (atleast 8mm), visibility and
venous anatomy needs to be analysed preoperatively or soft tissue attenuation of nodule on mediastinal window.
while evaluation of suspected hypervascular tumor in chest. Tube voltage is kept at 100kVp for better contrast‑to‑noise
ratio while the tube current is modulated according to
There are two basic modes of performing dynamic patient size. Following injection of contrast, serial breath
contrast‑enhanced CT (DCE‑CT): the more widely available hold acquisitions are performed at 60 s, 120 s, 180 s and 240 s.
and established technique uses multiple scan acquisitions Slice thickness is kept at 3 mm, with 2mm reconstruction
at pre‑determined time delays with respect to the initiation interval. Nodule analysis is performed in mediastinal
of contrast injection, while the newer ‘first pass’ technique window (width: 400 HU, level: 40 HU) in axial plane. The
evaluates the initial passage of contrast media though the analysis of resultant image set involves measurement of
intravascular space by acquiring a baseline non‑contrast peak mean nodule enhancement and time‑attenuation curve
image followed by a series of images after contrast which can be performed on most of the routinely available
administration. Analysis of the temporal changes in the commercial software.
contrast enhancement of the tissues allows generation
of various perfusion‑related parameters that reflect the Perfusion CT/Dynamic ‘first pass’ CT
vascular status of the tissue being studied.[30] The former Dynamic first pass contrast–enhanced perfusion CT
more conventional approach to DCE‑CT is routinely (DCE‑CT) has been used by various investigators for
available on the current scanners and has more clinical quantitative assessment of perfusion parameters for
acceptability while the latter is largely considered a research characterization of pulmonary nodules or masses, as well
tool with limited availability. as for early assessment of treatment response in lung
cancer following chemotherapy.[33‑36] The current role of
Dynamic multiphase CT DCE‑CT is more as a complimentary modality to established
The more conventional approach involves 5‑6 images investigations as CT and 18F FDG PET‑CT for lesion
acquired through the nodule at fixed time intervals characterization. The CT protocol outlined in the present
post contrast injection. This aids in characterization of review is based on the recommendations of on‑going
the pulmonary nodules as benign or malignant, based multi‑centric SPUtNik trial which assesses the diagnostic
performance, costs and health outcome of DCE‑CT as an
adjunct to 18F FDG PET‑CT for nodule characterization.
Prior to performing DCE‑CT, it is essential to evaluate the
suitability of the lesion using similar parameters as detailed
in dynamic multiphasic protocol.[32]

The institutional protocol being followed at the authors’

centre for evaluation of perfusion in lung carcinoma
A B uses dual‑source DECT scanner with 50 ml of contrast
(320 mg I/ml at 5 ml/second followed by 20 ml saline

C D A B C
Figure 12 (A-D): Single phase split‑bolus DECT angiography in a Figure 13 (A-C): Multiphasic CT for evaluation of nodule enhancement.
case of hemoptysis. (A and B) ROI positioning in ascending aorta Magnified image in mediastinal window of a nodule in left lower lobe.
with trigger at 100HU. (C and D) Simultaneous optimal opacification (A) NCCT and images acquired at 30 secs (B) and 70 secs (C) post
of aorta, pulmonary artery and their branches is seen contrast injection, show awash‑in of 19 HU

244 Indian Journal of Radiology and Imaging / Volume 29 / Issue 3 / July - September 2019
 Bhalla, et al.: Recommendations for imaging protocols for CT chest

Table 5: Key features of acquisition protocol of two subtypes of dynamic contrast‑enhanced CT

Dynamic multiphase CT Dynamic ‘first pass’/perfusion CT
Area of coverage 6 cm 7‑10 cm depending on tumour
Slice thickness 3 mm 5 mm
kVp 100 kVp 80 kVp
mAs According to patient’s weight: 80 mAs
<60 Kg, 200 mAs
60‑90 Kg, 350 mAs >90kg. 500 mAs
Rate of contrast 2ml/sec 5 ml/sec
Time delay/phase Pre‑contrast, 60 sec, 120 sec, 180 sec and 240 sec. Scan delay: 5 sec, 22 dynamic acquisitions: first 10 scans every 3 sec,
of acquisition next 5 scans every 2 sec and next 7 scans every 4 sec
Reconstruction Reconstruction interval: 2mm Reconstruction interval: 3 mm
Standard mediastinal window: (windowlevel: 40HU, width: 400HU) Standard mediastinal window: (windowlevel: 40HU, width: 400HU)
Parameter available Peak enhancement (HU), Wash in and wash out percentages Blood flow, blood volume, permeability, mean transit time, time to peak

flush). Z‑axis coverage varies from 7‑10 cm depending

on tumour. After a scan delay of 5 seconds, dynamic
acquisition of 22 scans are performed in free breathing
(first 10 scans every 3 seconds, next 5 scans every 2 seconds
and next 7 scans every 4 seconds). Tube voltage and
tube current are kept at 80 kVp and 80mAs, respectively. A B C
Image reconstruction is done at slice thickness of 5mm,
reconstruction interval of 3mm and mediastinal soft
tissue kernel. Six perfusion parameters are analysed
(peak enhancement intensity, blood flow, blood volume,
permeability, mean transit time and time to peak) using
two‑compartment analysis model [Figure 14].[37] The Table D E
5 below summarises the key features of two modes of
Figure 14 (A-E): Dynamic perfusion CT of large necrotic mass to choose
performing dynamic contrast enhanced CT for pulmonary appropriate site of biopsy. (A) Axial maximum intensity projection
nodules and masses. (MIP) image in mediastinal window shows large necrotic mass in
right hemithorax, with peripheral thick irregular nodular enhancement
Paediatric Application of CT Chest Protocols (white arrow) and associate collapse of lung (blue arrow).Color‑coded
blood flow (B), blood volume (C) and permeability (D) maps showing
increased perfusion in peripheral nodular areas of enhancement (white
While most of these protocols would be applicable to arrow) with hypoperfused necrotic centre. Distally collapsed lung shows
children, but typically multiphasic CT imaging should be homogeneous high perfusion (blue arrow). (E) Image showing technical
parameters of the acquisition
restricted in children, and dynamic CT perfusion is almost
never used for characterisation. Substitution with USG and
MRI should be considered whenever feasible. Additional standardized thoracic CT protocols to allow for uniformity
equipment and vendor specific features of dose reduction and consensus opinion across institutions.
should be adopted, and general principles of ALARA
Financial support and sponsorship
e.g. restriction of coverage should be adhered to even more
Nil.
strictly. Elaborating on the specific paediatric protocols
in terms of sedation, contrast doses, radiation concerns is
Conflicts of interest
beyond the scope of this article.
There are no conflicts of interest.
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