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Technology Update

‘Reconstructed radiographs’ from MDCT volumedata: Why to still ask for a conventional radiograph,after CT is done?

Nitin P. Ghonge*

Department of Radiology, Indraprastha Apollo Hospital, New Delhi 110076, India

a r t i c l e i n f o

Article history:

Received 28 June 2014

Accepted 24 July 2014

Available online xxx

Keywords:

‘Reconstructed radiographs’

MDCT

Mean intensity projection method

(mean-IP)

Average intensity projection

* Tel.: þ91 9811135957.E-mail addresses: drnitinghonge@rediffm

Please cite this article in press as: Ghongventional radiograph, after CT is done?, Apo

http://dx.doi.org/10.1016/j.apme.2014.07.0150976-0016/Copyright © 2014, Indraprastha M

a b s t r a c t

‘MDCT-reconstructed radiographs’ is a radiograph generated from the MDCT volume data.

It is important to be aware of the ability of MDCT to generate ‘reconstructed radiographs’

with use of mean-intensity projection or average intensity projection (mean-IP or average-

IP) and its potential clinical applications. Whenever there is a need for radiograph after CT

is already done, clinicians may ask for ‘MDCT reconstructed radiographs’ rather than

conventional radiograph. This will also ensure that the volume acquisition during MDCT

study which has already subjected the patient to radiation dose is optimally post-

processed to extract the maximum information and the need for any further radio-

graphic exposure is minimized. This clinical practice is likely to minimize the need for a

conventional radiograph in a wide range of clinical conditions, after CT is done; as illus-

trated in this pictorial communication.

Copyright © 2014, Indraprastha Medical Corporation Ltd. All rights reserved.

1. Introduction

In the last few decades, the role and relevance of Multi-

detector CT (MDCT) has rapidly evolved in clinical practice

for a wide range of indications. MDCT is now truly an imaging

‘workhorse’ in the modern healthcare system.1 The marked

increase in the number of CT referrals also indicates the high

acceptance rates for CT as an imaging modality of choice,

among the clinicians. As MDCT allows acquisition of volume

data, wide range of post-processing options are available,

which can be generate images in two-dimensions or three-

dimensions. Depending upon the clinical indication or

ail.com, drnitinpghonge@

e NP, ‘Reconstructed radllo Medicine (2014), http

edical Corporation Ltd. A

imaging findings, MDCT reconstructions can be performed

along the desired planes. These planes can be along the

anatomical structure like ureter or pancreatic duct or along

the disease process. Post-processing methods like Maximum

Intensity Projective (MIP), Minimum Intensity Projection (min-

IP), Shaded Surface Display (SSD) & Multi-Planer Reformation

(MPR) are widely used in the Radiology departments and are

well accepted by the Clinicians, across the globe.2

Despite this popularity of CT, the clinicians in general, still

consider CT as a means of cross-sectional imaging only. The

ability of MDCT to transform the volume data into ‘recon-

structed radiographs’ with use of mean-intensity projection

or average intensity projection (mean-IP or average-IP)

gmail.com.

iographs’ from MDCT volume data: Why to still ask for a con-://dx.doi.org/10.1016/j.apme.2014.07.015

ll rights reserved.

mailto:[email protected]

mailto:[email protected]

www.sciencedirect.com/science/journal/09760016

www.elsevier.com/locate/apme

http://dx.doi.org/10.1016/j.apme.2014.07.015



Fig. 1 e Frontal reconstructed radiograph (A) and conventional radiograph (B) of chest. Conventional radiograph certainly

offers higher spatial resolution, as pulmonary vascular details as better seen in B. Reconstructed radiograph however, offer

greater flexibility and minimize interference from the overlapping structures.


method is not widely known to clinicians. The clinician often

advises conventional radiographs, even after the CT is per-

formed. This trend is quite common and is often related to

clinician's comfort level with the conventional radiographs as

compared to cross-sectional images. This leads to unnec-

essary requests for the radiographs. CT imaging involves

much higher doses of radiation when compared with plain-

film radiography.3 It is mandatory to extract the maximum

information from the CT study and any need for further

radiographic exposure should be minimized. Though, radio-

graphs account formuch lower radiation exposure to patients;

it does unnecessarily increase the overall radiation dose to the

patients, who already had a CT examination.

The purpose of this illustrative communication is to create

awareness about ‘reconstructed radiographs’, which can be

generated from the MDCT volume data and utilized in routine

practice for a wide range of clinical indications.

2. MDCT ‘reconstructed radiograph’ e meanintensity projection [mean-IP] method

Radiographs can be reconstructed using the MDCT datasets,

provided the spiral acquisition of the volume data is acquired

Fig. 2 e Reconstructed frontal radiograph of chest can be genera

(A) and other adjusted according to posterior chest (B). Adjustme

specific anatomical region of chest in a reconstructed radiograp

while anterior ends of the ribs and the cardiac margins are not

Please cite this article in press as: Ghonge NP, ‘Reconstructed raventional radiograph, after CT is done?, Apollo Medicine (2014), http

using the narrow collimation. The thin volume data can be

subsequently utilized to create the reconstructed radiograph

using mean intensity projection [mean-IP] method on pro-

cessing workstations. In contrast to MIP images used for CT

angiography, (which utilizes maximum attenuation values

fromthe imagingslab) andmin-IP imagesused for lung imaging

(which utilizesminimum attenuation values from the imaging

slab), the mean-IP method summates the mean attenuation

values of the imaging slab. ‘Reconstructed radiograph’ there-

fore represents themean or average attenuation values across

thevolumedata,whichcanbeviewed fromdesiredprojections.

The processing is fast and does not significantly add to the

computer memory. The generated ‘reconstructed radiograph’

can be filmed or saved on CD-ROM [Fig. 1].

3. Advantages of MDCT ‘reconstructedradiographs’

Unlike the conventional radiographs, the reconstructed ra-

diographs offer flexibility in terms of the imagemanipulation.

Image manipulation includes window level and width set-

tings, which allows highlighting the body regions of particular

CT attenuation. This is also feasible with digital radiographic

ted as two separate images, one adjusted to anterior chest

nt of the window level and width settings will highlight the

h. Note that posterior ends of the ribs are not seen in A,

seen in B.

diographs’ from MDCT volume data: Why to still ask for a con-://dx.doi.org/10.1016/j.apme.2014.07.015



Fig. 3 e Reconstructed radiographs e frontal projection of paranasal sinuses (A) and lateral projection of neck (B) provides

excellent delineation of the regional anatomy with minimum overlap from the adjoining structures. Small impacted foreign

body is seen in the posterior hypopharyngeal wall (arrow).

a p o l l o m e d i c i n e x x x ( 2 0 1 4 ) 1e7 3

images which offer higher spatial resolution. But with MDCT

reconstructed radiographs, the reconstruction coordinates

can be adjusted to highlight the particular depth of the volume

data. This flexibility allows a set of radiographs for a particular

body region. For example, the ‘reconstructed’ chest

Fig. 4 e Degenerative arthropathy of right hip joint. MDCT max

attenuation of right hip joint space with presence of sub-articul

lateral (C) reconstructed radiographs provide a true radiographic

separate conventional radiographs.

Please cite this article in press as: Ghonge NP, ‘Reconstructed radventional radiograph, after CT is done?, Apollo Medicine (2014), http

radiograph can be shown as two separate images, one

adjusted to anterior chest and the other one adjusted ac-

cording to posterior chest [Fig. 2]. These adjustments allow

creation of set of radiographs to highlight the different parts of

the region being evaluated. Themaximum thickness available

imum intensity projection image (A) showing gross

ar cysts and sclerotic changes (small arrow). Frontal (B) and

rendition of joint pathology (long arrows) without need for




Fig. 5 e Reconstructed radiographs of chest in frontal projection show anterior junctional line (A, arrows) and the right para-

tracheal stripe (B, arrow).


on the software interface for the mean-IP image reconstruc-

tion is 128 mm. This is likely to constitute an important lim-

itation in conditions, when the volume data is significantly

thicker than 128 mm, as in a particularly obese patient. It is

therefore necessary to create a set of radiographs to highlight

the anterior and posterior body regions separately, to convey

the complete thickness of the volume data.

Reconstruction of MDCT data to create radiographs also

ensure that radiographic views, which are difficult to acquire

with use of film radiography or computed radiography are

easily reconstructed, without any need for patient movement

or positioning. Apart from the standard frontal, lateral and

oblique views, the reconstructed radiographs allow use of

Fig. 6 e Reconstructed radiographs of chest (lateral projection) s

(B). In contrast to conventional lateral radiograph of chest, recon

left hilum with minimum overlap of structures.


non-conventional planes. Use of reconstructed radiographs

offers an additional advantage for the patients with trauma

who had unstable fractures and cannot be mobilized for the

optimal radiographic views. Once the volume data is acquired

with MDCT, the reconstructed radiographs in different ori-

entations can be generated without the need for any addi-

tional patient movement or discomfort or any need for

separate radiographic exposures.

Current CT scanners are capable of generating thin

submillimeter-thickness images in routine studies. The

sliding-slab mean or average intensity projection technique

renders overlapping data slabs of a pre-determined thickness

with illusion of image-to-image continuity. The illusion of

howing the structures in right hilum (A) and the left hilum

structed radiographs allows separate images for right and




Fig. 7 e Reconstructed chest radiograph (frontal projection) shows an ill-defined area of consolidation in right upper lobe

(long arrow) in a patient with infective pneumonitis (A). Reconstructed chest radiograph (frontal projection) shows a large

cavitory lesion (short arrow) in right upper lobe in another patient with lung malignancy. Metastatic lung lesions are also

seen on the left side (arrowheads).


image-to-image continuity is useful in vascular assessment.

This method thus ensures that the image quality is improved

without any increase in radiation dose. Due to these advan-

tages, the sliding-slab technique can potentially become a

primary mode of image interpretation in CT studies done on

isotropic voxel scanners.4,5

Fig. 8 e Reconstructed frontal radiograph of KUB region

using the delayed phase MDCT urography images provides

the overview with an ‘IVP-like’ image, which is often more

acceptable to the referring Urologist.

4. MDCT ‘reconstructed radiograph’ inclinical practice

Reconstructed radiographs from the MDCT dataset can be

created for different body regions and can be utilized for a

wide range of clinical application, as an alternative to con-

ventional radiographs. Reconstructed radiographs offer

optimal information about the para-nasal sinuses, skull and

soft tissue structures of neck including the airways [Fig. 3].

Radiography of the spine is commonly performed for a variety

of clinical indications including trauma, infections, tumors,

developmental lesions and in post-operative period. Recon-

structed radiographs however, cannot serve as an alternative

to dynamic conventional radiographs performed in flexion-

extension or standing patient positions. Pelvic and hip radio-

graphs are routinely advised for trauma, infections, tumors

and wide range of musculo-skeletal abnormalities. Several

standard and non-standard views can be obtained with use of

reconstructed radiographs to delineate the regional anatomy

[Fig. 4].

Chest Radiograph is one of the most commonly advised

radiographs in clinical practice. Apart from trauma, infections

and tumors, chest radiographs are routinely advised as a part

of pre-operative and for post-operative evaluation. Conven-

tional radiographs are the suitable options for the pre-

operative work-up of patients, if CT chest is not available.

Reconstructed radiographs offer excellent delineation of

several important anatomical landmarks in the chest in

frontal [Fig. 5] and lateral [Fig. 6] projections. These radio-

graphs are therefore useful alternative options for wide range

of clinical indications, if CT chest is available [Fig. 7]. It is


important to understand that the patient is in supine position

and accordingly the radiographic appearances in state of

normalcy and disease will be altered. Studies have empha-

sized on the various aspects of nodule detection in digital

chest radiographs including the impact of anatomical location




Fig. 9 e In patient with poly-trauma, whole-body MDCT data can be processed to generate ‘reconstructed radiographs’ with

wide field-of-view (A). Reconstructed radiographs with small field-of-view for specific regions can be subsequently created

as illustrated here for pelvis in frontal (B) and lateral (C) projections and left thigh in frontal (D) and lateral (E) projections.

Linear undisplaced fracture of left acetabulum and communited fracture of left distal femur are better delineated with

reconstructed radiographs (arrows). With poor patient compliance in these settings, conventional radiographs may show

poor quality and subject the patient to risk of further dislocation during positioning.


of the lung nodule and the system noise. Use of radiographs

reconstructed from MDCT is therefore more likely to convey

the complete information, as compared to a conventional

radiograph.6e8

The mystique of bowel-gas pattern can be more effectively

evaluated with use of reconstructed radiographs of abdomen.

The use of separate reconstructed radiographs for the anterior

and posterior parts of the abdominal cavity allows clear un-

derstanding of bowel-gas pattern and the underlying disease

process. The presence of free intra-peritoneal air should be

expected along the anterior abdominal wall rather than in

sub-diaphragmatic locations. Despite the widespread use of

CT urography, the fondness of urologists for intravenous

urography (IVU) does not seem to wane. Few urologists still

prefer to ask for an IVU study or for a delayed abdominal

radiograph after the contrast is injected for CT urography.

This does expose the patient to an additional radiation,

discomfort and cost. At the same time, this causes additional

burden for a busy radiology department. Reconstructed ra-

diographs serve as a perfect remedy for these circumstances,

as IVU-like images can be generated from the CT data [Fig. 8].

Due to poor patient compliance, the image quality of con-

ventional radiographs in accident and trauma settings is often

sub-optimal. The use of reconstructed radiographs is partic-

ularly useful in poly-trauma settings. MDCT study of these

patients ensures prompt and comprehensive assessment of

osseous, soft tissue and vascular structures. Due to volume


acquisition and post-processing, MDCT scanning is flexible in

terms of patient position and does not need the patient to lie

in a particular position. Reconstructed radiographs can be

then generated from MDCT data, without any additional time

delay, radiation exposure or risk of further dislocation at the

fracture sites. Whole-body MDCT acquisition provides

detailed information about the osseous and soft tissue injury

in patientswith polytrauma [Fig. 9]. In fact,Whole-bodyMDCT

is now suggested as the ‘one-stop’ investigation in patients

with polytrauma. It is important to adhere to this clinical

practice in patients with trauma, with routine use of recon-

structed radiographs.9e11

5. Conclusions

It is important to understand the ability of MDCT to transform

the volume data into ‘reconstructed radiographs’ with use of

mean-intensity projection or average intensity projection

(mean-IP or average-IP). This is an additionalmethod of MDCT

post-processing, which is available at the click of mouse and

the final image looks like a radiograph. If there is need for a

radiograph in patient, after CT study is already done; Clini-

cians may ask for ‘MDCT reconstructed radiographs’ rather

than conventional radiographs. If a reconstructed radiograph

does not serve the purpose, then conventional radiograph can

always be performed.





In view of radiation concerns with use of CT in clinical

practice, it is worth reiterating that CT should be performed

only if there is appropriate clinical indication. Study protocol

should be tailored according to scan indication with use of

optimal radiation dose based on ‘as low as reasonably

achievable’ [ALARA] principles. Post-processing and image

interpretation methods should then ensure that maximum

information is extracted from the acquired data.

‘MDCT-reconstructed radiographs’ with use of ‘mean-IP’

images is a useful additional method to attain these

objectives in clinical practice. This is likely to minimize the

need for a conventional radiograph in a wide range of clinical

conditions.

Conflicts of interest

The author has none to declare.

r e f e r e n c e s

1. Ghonge NP. Computed tomography in the 21st century-current status and future prospects. J Int Med Sci Acad (JIMSA).2013 (JaneMar);26(1):35e42.

2. Fishman EK, Ney DR, Heath DG, Corl FM, Horton KM, John PT.Volume rendering versus maximum intensity projection inCT angiography: what works best, when, and why?RadioGraphics. 2006;26:905e922.


3. Brenner David J, Hall Eric J. Computed tomography e anincreasing source of radiation exposure. N Engl J Med.2007;357:2277e2284.

4. Lee KH, Kim YH, Hahn S, et al. CT diagnosis of acuteappendicitis: advantages of reviewing thin-section datasetsusing sliding slab average intensity projection technique.Invest Radiol. 2006;41:579e585.

5. Kim B, Lee KH, Kim KJ, Mantiuk R, Kim H, Kim YH. Artifacts inslab average-intensity-projection images reformatted fromJPEG 2000 compressed thin-section abdominal CT data sets.Am J Roentgenol. June 2008;190(6):W342eW350.

6. Moore CS, Liney GP, Beavis AW, Saunderson JR. A method toproduce and validate a digitally reconstructed radiograph-based computer simulation for optimisation of chestradiographs acquired with a computed radiography imagingsystem. Br J Radiol. 2011;84(1006):890e902.

7. Bath M, Hakansson M, Borjesson S, et al. Nodule detection indigital chest radiography: effect of anatomical noise. RadiatProt Dosim. 2005;114:109e113.

8. Sund P, Bath M, Kheddache S, Mansson LG. Comparison ofvisual grading analysis and determination of detectivequantum efficiency for evaluation system performance indigital chest radiography. Eur Radiol. 2004;14:48e58.

9. Nguyen D, Platon A, Shanmuganathan K, Mirvis SE,Becker CD, Poletti PA. Evaluation of a single-pass continuouswhole-body 16-MDCT protocol for patients with polytrauma.Am J Roentgenol. 2009;192:3e10.

10. Linsenmaier U, Kr€otz M, H€auser H, et al. Whole-bodycomputed tomography in polytrauma: techniques andmanagement. Eur Radiol. 2002 Jul;12(7):1728e1740.

11. Standards of Practice and Guidance for Trauma Radiology inSeverely Injured Patients. The Royal College of Radiologists;2011. ISBN: 978-4-905034-51-2. Ref No. BFCR(11)3.


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