Vol.3, No.5, 292-299 (2011)
opyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
Exploring the useful exposure range limits of three
intraoral image receptors for various tube potential,
tube current and exposure time settings
Elli Katsoni1*, Ioannis A. Tsalafoutas2, Panagiotis Gritzalis3, Evripides Stefanou3,
Evangelos Georgiou1, Emmanouel Yakoumakis1
1Department of Medical Physics, Medical School, University of Athens, Athens, Greece;
*Corresponding Author: jzar@rocketmail.com
2Medical Physics Department, Agios Savvas Hospital, Athens, Greece;
3Department of Oral Diagnosis and Radiology, Dental School, University of Athens, Athens, Greece.
Received 28 February 2011; revised 20 April 2011; accepted 4 May 2011.
Objectives: To determine the useful exposure
range limit s of three intraoral image r eceptors of
different technology when exposed to different
X-ray beam spectra, dose and dose rate levels.
Study Design: A dental X-r ay unit offering a wide
range of tube potential, tube current and expo-
sure time settings was used to expose a dental
quality control phantom. The receptors that
were used to capture the radiogr aphic im ages of
the phantom were: the Kodak Insight, the Koda k
RVG-6000 and the Duerr Vistascan system. The
images that were produced over a wide range of
exposure factor settings were evaluated in
terms of dia gnostic qual ity by three e xperienc ed
radiologists. Results: The number of images
with acceptable diagnostic quality was in total
1257; 310 with Insight, 331 with RVG 6000 and
616 with Vistascan. At 60 kV, diagnosable im-
ages were produced with doses ranging from
0.44 - 1.56 mGy for the Insight film 0.44 - 2.82
mGy for the RVG 6000 and 0.22 - 4.93 mGy for
the Vistascan system. At 70 kV, the respective
ranges were 0.39 - 1.28 mGy for the Insight film
0.31 - 2.55 mGy for the RVG6000 and 0.30 - 3.46
mGy for the Vistascan system. Conclusions:
The Vistascan exhibited the widest useful ex-
posure rang e an d r equ ir ed th e l eas t ex pos ur e to
produce a diagnosable image at almost all tube
potential settings. The RVG 6000 exhibited a
slightly wider useful exposure range than the
Insight film, with almost the same dose re-
quirements especially in higher Kv settings.
Keywords: Radiography, Dental, Digital; Dosage
According to the UNSCEAR 2000 Report, dental in-
traoral radiography is among the most frequently per-
formed radiological procedures [1]. Although the patient
exposure associated with dental radiography is relatively
low, intraoral radiography should be optimised in order
to keep the radiation risk “as low as reasonably achiev-
able”, something that is widely known as the ALARA
principle [2].
Over the past 20 years both the X-ray units and the
X-ray receptors used in dental radiology have been
evolved. Modern dental X-ray units incorporate high
frequency generators, operate at higher tube potentials
and produce X-ray spectra that have higher mean energy
and therefore are more penetrating compared to those
produced by older dental X-ray units. These improve-
ments have contributed in the reduction of the radiation
dose to the entrance skin surface of the patient and the
enhancement of image quality. Concerning the X-ray
receptors, new digital systems have been introduced in
to the clinical practice and nowadays digital radiography
is considered an accepted imaging technique in dentistry.
Currently, solid-state detectors based on CCD or CMOS
technology, photostimulable storage phosphor (PSP)
systems, along with the old-fashioned but still widely
used silver halide based films, are commercially avail-
able for intraoral radiography.
In the international literature many remarkable articles
can be found describing digital receptor systems and
presenting comparisons among various systems with
regard to their diagnostic performance [3-7]. Their re-
sults, however, have been derived using a limited range
of exposure factors, despite the fact that the response of
films and solid state or PSP receptors is dependent on
the energy spectrum of the X-ray beam used and the
E. Katsoni et al. / Health 3 (2011) 292-299
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
dose levels to which they are exposed. The influence of
the exposure factors on the performance of dental re-
ceptors of different technologies has not yet been inves-
tigated extensively.
The purpose of this study was to comparatively evalu-
ate, in a systematic inter-equipment manner, the useful
exposure range of three intraoral image receptors which
are representative of the currently available technologies,
when exposed to different X-ray beam spectra, dose and
dose rate levels.
A modern dental X-ray unit (Prostyle Intra DC, Plan-
meca Oy, Helsinki, Finland) was used, offering eight
tube potential settings (ranging from 50 to 70 kVp),
seven tube current settings (ranging from 2 - 8 mA) and
26 exposure time settings (ranging from 0.01 to 3.2 sec).
The nominal total filtration was 2 mm Al and the focus
to collimator end distance was 30 cm.
A calibrated ion chamber dosimeter (Dosimeter 9010,
ionization chamber type 90x6-6; Radcal Corporation,
Monrovia, USA) positioned at 30 cm from the tube fo-
cus was used to measure the dose in free air and deter-
mine the tube output at that distance. These measure-
ments were carried out for all the available tube potential,
tube current and exposure time selections, in order to
identify possible variations in output with different tube
loading values. The tube potential accuracy and repro-
ducibility were checked using a calibrated kilovolt peak
meter (Gammex RMI 245, Gammex Inc., Middleton,
The intraoral radiographic receptors evaluated in this
study were: the Kodak Insight F speed class film (East-
man Kodak Company, Rochester, NY), the Kodak RVG
6000 (Eastman Kodak Company, Rochester, NY), and
the Duerr Vistascan Combi PSP system (Duerr Dental,
Bietingsheim-Bissingen, Germany). The main technical
characteristics of the systems tested are summarized in
Table 1.
A cylindrical Perspex based phantom (Dental Image
Quality Test Tool, model 76025; Nuclear Associates,
Division of Victoreen, Inc, Carle Place, NY) was used
for the evaluation of image quality [8]. This phantom
contains a real human tooth in the centre and around it
three cylindrical air filled holes of different height. In the
periphery of the phantom four wire meshes of different
wire thickness are included. Finally, the phantom has a
slot in order to fit in the various image receptors. A pho-
tograph and a radiographic image of the phantom are
shown in Figure 1 and Figure 2, respectively.
The phantom was attached to the collimator end and
the image to receptor distance was kept constant at 35 cm.
The phantom was radiographed using all the image re-
ceptors and for each receptor all the tube potential, tube
current and exposure time combinations possible. Thus,
1456 exposures were required for each image receptor in
The films were processed immediately after exposure,
with an automatic processor (Velopex Extra-X, Medivance
Instuments, England) using the Readymatic dental de-
veloper and Readymatic dental fixer solutions (Eastman
Kodak, Rochester NY), at a temperature of 27˚C. This
processor features an automatic replenishment system,
however, in order to ensure that the processing condi-
tions remain fairly constant during the experiments, the
processing stability was repeatedly tested every 50 films
using sensitometry (Pehamed densitometer Densinorm
21, PEHA med. Geräte GmbH Sulzbach, Germany). The
acquired film radiographs were mounted in opaque plas-
tic holders and coded for later use. The film radiographs
were evaluated on a viewing box, with all extraneous
light masked.
For the Vistascan the PSP image plates were unpacked
in a dimly lit room and scanned immediately after expo-
sure, using the Vistascan Combi system [9,10]. The
scanner’s resolution pitch settings were adjusted to 12.5
μm (corresponding to a theoretical resolution of 40 line
pairs per mm). Concerning the RVG 6000 the original
software of the system was used for image capture. No
image processing was performed to enhance image qual-
ity other than the system’s default pre-process.
All digital images were viewed in fit to screen mode
Table 1. Specifications of the systems.
Model ManufacturerPixel Size
(μm) Technology Software Size Bit/PixelWidth
File Size
HALIDE N/A 2 N/A 3.1 (cm) 4.1 (cm)N/A
RVG 6000 KODAK 18.5 × 18.5 CMOS
1 8 1200 1600 1.8
12.5 IMAGE PLATEDBSWIN V.3.32 16 2476 3195 Up to 9.3
E. Katsoni et al. / Health 3 (2011) 292-299
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Figure 1. Photograph of the phantom used for the evaluation
of image quality.
Figure 2. Radiographic image of
the phantom used for the evalua-
tion image quality.
on a 19-inch TFT monitor (Sony SDMHS95PR), with
1280 × 1024 resolution under subdued lighting conditions.
The monitor’s brightness and contrast were adjusted
using the SMPTE (Society of Motion Picture and Tele-
vision Engineers) test pattern [11,12].
All the images acquired were evaluated by three ex-
perienced radiologists in the department of Oral Diagno-
sis and Radiology of the Dental School of the University
of Athens. For each image, the observers evaluated the
cementoenamel junction, the dentoenamel junction, the
root canals and the apical region of the tooth, as well as,
the perceptibility of the three holes and the four
wire-mesh areas included in the phantom. An image was
considered to have adequate diagnostic quality when all
the aforementioned anatomical characteristics of the
tooth were properly imaged and additionally the holes
and the wire meshes were discernible. It had been de-
cided that in case of disagreement among the observers,
the images in question would be reviewed for a second
time and if disagreements were not resolved, the opinion
of the majority would be adopted.
The output measurements revealed that the linearity of
output was within accepted limits at all tube potentials,
even though for small tube loadings ( 0.5 mAs) a re-
duction in output of up to 20% was observed with re-
spect to the mean value of output over the whole mAs
range. The reproducibility of output using the same ex-
posure conditions was found to be better than 1%. The
tube potential accuracy and reproducibility were found
better than 3% and 1%, respectively.
For all the images of acceptable quality, the receptor
type, the exposure factors (kV, mA, s) were noted and
the respective entrance surface air kerma (ESAK) values
at the phantom were then assigned. Examples of such
images derived for a given combination of tube potential
and tube current and varying exposure time, are embed-
ded in Table 2, which is indicative of the differences
observed among receptors with respect to their useful
exposure range.
Concerning the images of insufficient quality that
were considered non-diagnosable, these included the
under and over exposed films and those digital images in
which the appearance of the phantom resembled those of
over or under exposed films, as well as, digital images
with excessive noise or other artifacts (partial inversion
of the greyscale in parts of the image, blooming effects
The number of images with acceptable diagnostic
quality was in total 1257; 310 with Insight, 331 with
RVG 6000 and 616 with Vistascan. An overview of the
useful exposure range of all receptors is presented (Fig-
ure 3). In this figure the exposure range of each receptor
is presented with respect to the nominal mAs (left side)
and the ESAK (right side), for all tube potential settings.
For reasons of straightforward comparison among re-
ceptors in all insert figures the same axis scale was used.
From Figure 3, it is obvious that the VistaScan PSP sys-
tem exhibited by far the most extended useful exposure
range for all the tube potential values used. Furthermore,
it required the least dose to produce a diagnosable image
at all tube potentials except 50 and 55 kV, where the
Insight film required less and exactly the same ESAK,
respectively. The second wider useful exposure range
was exhibited by the RVG 6000. However, it required a
slightly higher minimum ESAK to produce a diagnos-
able image compared to the Insight film, except from 60
and 70 kV where the RVG 6000 required exactly the
same and less dose, respectively. The Insight film exhib-
ited a relatively limited useful exposure range but in
terms of the minimum ESAK required to produce a di-
agnosable image, it was the second after the Vistascan.
Indicatively at 60 kV the useful exposure ranges of the
VistaScan PSP, RVG 6000, Insight and were 0.22 - 4.93,
0.44 - 2.82 and 0.44 - 1.56 mGy, respectively. At 70 kV,
the respective ranges 0.30 - .46 mGy, 0.31 - 2.55 mGy 3
E. Katsoni et al. / Health 3 (2011) 292-299
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Table 2. Images with satisfactory image quality obtained at 70 kV and 4mA with the three different receptors. The exposure time and
the respective ESAK are given in the bottom rows.
RVG 6000
sec 0.1 0.125 0.16 0.20 0.25 0.32 0.4 0.5 0.64 0.8 1
mGy 0.33 0.41 0.53 0.67 0.83 1.07 1.34 1.68 2.16 2.70 3.38
Figure 3. The useful exposure range of the three receptors studied is given for all tube.
E. Katsoni et al. / Health 3 (2011) 292-299
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and 0.39 - 1.28 mGy.
One may notice that a discrepancy exists among the
width of useful exposure ranges of Insight film and the
RVG 6000 as shown in Figure 3 and the respective
number of diagnosable images mentioned above. This is
due to the fact that RVG 6000 exhibited a dependency
on the dose rate, since for a specific tube potential set-
ting and different mA selections, the same ESAK some-
times produced a diagnosable image and sometimes a
non-diagnosable image. This can be seen in Figure 4
where the useful exposure range is given for each tube
loading setting separately, for tube potentials settings of
60 and 70 kV, which are the most frequently tube poten-
tial settings encountered in modern X-ray units. In this
figure it can be seen that RVG 6000 exhibited a better
response at low dose rates (i.e. lower mA settings).
Concerning the images of insufficient quality, these
included the under and over exposed films and those
digital images in which the appearance of the phantom
was resembling this of over or under exposed films and
images with excessive noise and artifacts. Some charac-
teristic examples of the non diagnosable images and er-
ror images obtained with the three receptors have been
gathered in Figures 5(a) to 5(h).
It can be seen that while in Figure 5(a) the appear-
ance of the digital image obtained with the RVG 6000
receptor was similar to that of an overexposed film, fur-
ther increase of the exposure time produced the noisy
image of Figure 5(b), in which the greyscale was auto-
matically inverted. A similar situation is presented in
Figures 5(c) to 5(e). With tube potential and tube current
constant, starting from a digital image that was looking
like an overexposed film (Figure 5(c)), further increase
of the exposure time produced initially an image that
was almost black (Figure 5(d)) and then an image where
the phantom structures reappeared to some extent but
with inverted greyscale (Figure 5(e)).
In Figures 5(f) and 5(g) the appearance of an under-
exposed and an overexposed image with the Vistascan
receptor, respectively, are shown. Finally, in Figure 5(h)
Figure 4. The useful exposure range of the three receptors studied is given for each one of the tube current settings used, for a tube
loading of 60 (left figure’s side) and 70 kV (right figure’s side). Each diagnosable image is represented by a data point.
E. Katsoni et al. / Health 3 (2011) 292-299
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(a) (b) (c) (d)
(e) (f) (g) (h)
Figure 5. Examples of images that were rejected due to lack of image quality and error images that when the exposure was repeated
they resulted in diagnosable images. Rejected images with the RVG 6000 receptor; (a) 50 kV, 8 mA, 1.6 sec, (b) 50 kV, 8 mA, 2.5 sec,
(c) 63 kV, 8mA, 0.64 sec, (d) 63 kV, 8mA, 0.8 sec, (e) 63 kV, 8mA, 1.6 sec. Vistascan (f) - (g), f) 70 kV, 8mA, 0.01 sec (g) 70 kV,
3mA, 3.2 sec, (h) 55 kV, 8mA, 0.01 sec. Error images with the RVG 6000 (k) receptor.
an error with the RVG 6000 receptors is shown. This
error was attributed to some kind of “fatigue” that the
detectors may have experienced during successive ex-
Diagnosable image refers to a quality radiograph in
which the examined anatomic structure is captured with
fidelity. Image quality describes the subjective judgment
by the clinician of the overall appearance of a radiograph.
It combines the features of density, contrast, latitude,
sharpness, resolution and perhaps other parameters.
Various mathematical approaches have been used to
evaluate these parameters further, such the detective
quantum efficiency (DQE) that encompasses image con-
trast, blur, speed and noise. Often a system can be opti-
mized for one of these parameters, but this is usually
achieved at the expense of others. However, more in-
formation is needed for complete understanding of all
the factors responsible for the subjective impression of
image quality. Three main factors that control quality are
receptor characteristics, geometric factors and subject
The wide exposure range of the storage phosphor
technology receptors, well known from their applica-
tions in general radiology, has been also confirmed in the
dental field [13-17]. The phosphor plate systems can
accommodate exposure times which are close to or at the
end of the electronic timer range of many commercially
available X-ray units. Since the radiographs from the
Vistascan receptor remained diagnosable from very low
to very high values of tube loading for all tube potential
values, no re-takes will be normally needed when this
type of receptor is used. On the other hand, it is also true
that with receptors of this type, higher doses than those
actually needed for diagnosis can be systematically used,
something that from the aspect of radiation protection is
considered disadvantageous and in general radiology it
has been reported as “the exposure factor creep” [18].
Concerning the minimum exposure that could give a
diagnosable image, as it can be seen in Figure 3, differ-
ences were observed among the three receptors tested,
especially for the lower kV settings used. However, for
the larger tube potential settings these differences were
quite smaller. At 70 kV the minimum required ESAK
value was about 0.3 mGy for the Vistascan and the RVG
6000, and about 0.4 mGy for the Insight. Regarding the
variation of the minimum ESAK required to produce
diagnosable images with the different tube potential set-
tings, the smallest variations were observed for Insight
(0.35 - 0.44 mGy) and the Vistascan (0.31 - 0.48 mGy).
The manufacturers of digital radiographic systems of-
E. Katsoni et al. / Health 3 (2011) 292-299
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ten claim that their systems offer a reduction in patient
exposure when compared to films. In the literature it is
also generally accepted that the patient dose is generally
lower in digital than in conventional film based intraoral
radiography with films of E-speed class [19-21]. How-
ever, in this study only the Vistascan produced diagnos-
able images at lower doses than the Insight film in all
tube potentials except at 50 kV, where it required more
dose and at 55 kV where it required exactly the same
The dependence of the response of RVG 6000 on the
dose rate was another interesting finding of this study.
The limitation of the useful exposure range of the RVG
6000 observed with the increase of tube current settings,
could be in part attributed to the difficulty of the receptor
controlling, in a linear and reproducible way, the ex-
tremely short exposure times.
European guidelines, in the context of the ALARA
principle, have recommended the establishment of diag-
nostic reference levels (DRLs) in dental radiography
[22]. Relevant surveys conducted in Greek dental radio-
graphic facilities over the last 10 years have demon-
strated a trend for reduction of the entrance surface dose
[8,23]. Hatziioannou et al. had suggested a DRL of 3.5
mGy for the intraoral dental equipment operating in
Greece [24]. However, in a recent study Gonzalez et al.,
have suggested a reference value of 1.8 mGy for E/F
speed class films and 0.6 mGy for the digital image re-
ceptors [25].
In this study it was shown that for the specific phan-
tom used, the Kodak Insight F speed class film required
doses quite smaller than the typical value suggested by
Gonzalez et al. [25] to produce images of satisfactory
diagnostic quality. On the other hand, regarding the
digital receptors the entrance dose of 0.6 mGy proposed
by Gonzalez et al. was outside the lower limit of the
useful exposure range of the RVG 6000 at tube poten-
tials of 50, 55 and 57 kV [25]. It is therefore obvious that
since the minimum dose required is strongly dependent
on the tube potential selection, any reference or DRL
values should also specify the tube potential range to
which they apply.
Since the vast majority of the dental X-ray units of
those commercially available and those currently in use
worldwide, offer a single or at best two tube potential or
tube current settings, it should not be taken for granted
that these are compatible with all commercially available
digital receptors.
Most modern dental X-ray units operate at a tube po-
tential value in the range of 60 to 70 kV. However, many
of them have only one tube current value setting that is
usually 7 mA and therefore, if combined with a digital
receptor of limited exposure range, only the very short
exposure time settings in the range of 0.1 to 0.3 sec
could be utilized for tube potentials larger than 60 kV
(assuming that these X-ray units have an output and a
total filtration similar to that of the unit used in this
study and that the same focus to receptor distance is
used). This problem will be more pronounced in dental
X-ray units with shorter collimators offering a minimum
focus to skin distance of about 20 cm (which is the case
for the majority of dental X-ray units), where only two
or three exposure time selections smaller or equal to 0.1
sec may be available for producing a diagnosable image.
However, in X-ray units which offer a tube current
around 4 mA as the standard or as an alternative selec-
tion, a wider range of exposure time settings can be util-
The differences observed in the useful exposure range
of the receptors tested, suggest that manufacturers
should include in the technical data sheets relevant in-
formation concerning the useful exposure range of their
receptors in terms of tube potential, ESAK and ESAK
rate in reference to a dental phantom (like this used or
any other that could serve as a reference dental phantom).
In this way the potential user would be able to determine
if a given receptor is compatible with the dental X-ray
unit that may already have and furthermore he/she would
be able to compare receptors using a performance index
that relates to the clinical practice and therefore is easy
to comprehend.
In conclusion, Vistascan presented the widest useful
exposure range compared to the RVG 6000 and the In-
sight film. At almost all tube potentials Vistascan re-
quired the least dose to produce a diagnosable image,
something that clearly is an advantage. On the other
hand, Vistascan could produce diagnosable image with
doses twice or three times the upper limit of the useful
exposure range of the RVG 6000 and the Insight, some-
thing that in the hands of an untrained dentist may be-
come a serious disadvantage. RVG 6000 exhibited a
wider useful exposure range than the Insight film with
almost the same dose requirements especially in higher
Kv settings.
We are grateful to the following companies: Dentomedica SA, Den-
tofair SA and Duerr Gmbh Germany, for supplying us with the image
detectors. We also thank our colleagues who served as observers.
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