Physica Medica: European Journal of Medical Physics - Volume 32 - Supplement 1 - February 2016

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Radiological Sciences and Public Health, University of Brescia, Brescia, Italy;
c School of Medical Physics, University of Milan, Milano, Italy; d Medical
Technology Laboratory, Rizzoli Orthopaedic Institute, Bologna, Italy;
e Neuroimaging Lab, Medical and Surgical Specialties, Radiological Sciences and
Public Health, University of Brescia, Brescia, Italy
Introduction: Bone volume fraction (BV/TV), trabecular thickness )
and trabecular separation are the structural parameters used to rep-
resent trabecular bone architecture. In general, micro computed tomography
(micro-CT) is considered the standard for evaluating human trabeculae but
it is limited to specimen due to FOV restrictions. In the present study the
spatial resolution of a CBCT scanner was characterized for in-vivo bone struc-
tural measurements and the derived trabecular parameters were compared
to micro-CT results.
Materials and Methods: For QR Newtom 5G CBCT installed at Spedali Civili
(Brescia, Italy) Noise Power Spectrum (NPS) and Modulation Transfer Func-
tion (MTF) were measured using Catphan600 phantom for different voxel
sizes (75, 100, 125, 150 μm). Four human specimens with different tra-
beculae concentrations were scanned by both CBCT and a Skyscan micro-
CT model 1072 (Bruker MicroCT, Konthich, Belgium) installed at Rizzoli
Orthopedic Institute (Bologna, Italy). For CBCT Gray Level Distributions (GLDs)
of trabecular volumes were compared among the different voxel sizes. Per-
centage differences and intercalibration curves were calculated between
CBCT (all voxel sizes) and micro-CT trabecular parameters.
Results: For CBCT, MTF curve moved toward right while NPS integral in-
creased when decreasing voxel size. GLDs representing bone marrow and
cancellous bone were resolved for all voxel sizes except for 75 μm. For all
voxel sizes CBCT systematically overestimated BV/TV and
Intercalibration curves were monotonic but not linear.
Conclusion: MTF improvement does not justify the use of the 75 μm voxel
size because of noise increase. GLDs comparison points out that the 150 μm
voxel size has the highest discrimination capability between bone marrow
and cancellous bone. Intercalibration curves against micro-CT are not linear
due to a CBCT saturation effect for higher trabecular concentrations, but
can be used to correct CBCT trabecular parameters.
B.276
PERFORMANCE EVALUATION OF DIFFERENT DIGITAL BREAST
TOMOSYNTHESIS SYSTEMS: DOSE AND IMAGE QUALITY ASSESSMENT
A. Maldera P. De Marco P.E. Colombo D.A. Origg A. Torresin
a Ospedale Niguarda Ca’ Granda, Milano, Italy; b Istituto Europeo di Oncologia,
Milano, Italy
Introduction: Digital Breast Tomosynthesis (DBT) is a recently intro-
duced technique for detection of breast cancer. The aim of this work is to
give a physical characterization of three commercial systems in order to
evaluate their performances in clinical practice.
Methods and Materials: The systems investigated are Senograph Essen-
tial® (GE), Mammomat Inspiration® (Siemens) and Selenia Dimensions®
(Hologic). They use different angular ranges (15°–50°), number of projec-
tions (9–25), type of acquisition (step and shoot – continuous) and
reconstruction algorithms (FBP – iterative).
Average Glandular Dose (AGD) and image quality parameters were assessed.
AGD was estimated with a calibrated ionization chamber according to the
model proposed by Dance.
Quality parameters of 3D images include spatial resolution evaluated
with the ‘‘in plane’’ modulation transfer function (MTF) (Zhao 2008), ‘‘in
depth’’ resolution (Marshall 2012) and signal difference to noise ratio
(SDNR).
The artifact was investigated measuring the Artefact Spread Function (ASF,
Wu 2004) of spherical details of various materials and diameters.
Results: Measured AGD was always below acceptable limits of full field
digital mammography (EUREF 2006).
We found the best “in plane” resolution on GE system; this could be related
to the used step&shoot acquisition modality. The “in depth” resolution, mea-
sured with the FWHM of a PSF in z-direction, improved with increasing
scan angle.
The Hologic system showed the best SDNR, probably due to its pixel binning,
while for the Siemens system low contrast detectability was poor.
As expected, ASF depends not only on detail dimension but is especially
sensitive to scan angle range: the persistency of the artifacts away from
the in-focus plane is larger for smaller range systems.
Conclusions: Physical characterization of DBT systems is important to eval-
uate dose and to determine image quality parameters, which can influence
clinical detectability of pathological tissues.
B.277
ESTIMATE ORGAN DOSE FROM CT EXAMINATION: A SOFTWARE
COMPARISON
A. Maldera M. Sutt A. Gaet M. Maddalo P.E. Colomb A. Torresi
a Ospedale Niguarda Ca’ Granda, Milano, Italy; b Spedali Civili Brescia, Brescia,
Italy
Introduction: Risk estimate in CT examination is directly connected to organ
dose calculation. The aim of this work is to evaluate the effect of simula-
tion parameters on organ dose estimation in CT examination with different
commercial software. In this study CT-Expo® (Sascrad, EX), ImpaCT Dose®
(CT Imaging GmbH, ID) and VirtualDose® (Virtual Phantoms Inc., VD) were
compared.
Materials and Methods: The most evident difference among SW is the
adopted phantom: EX and ID employ stylized phantoms, whereas VD in-
cludes a family of hybrid phantoms. Differences between adult phantoms,
adapted to ICRP “standard male and female” have been evaluated with CT
scan simulations that encompass the whole body.
VD and ID allow to simulate on phantoms with different body mass indices:
mean scan parameters of obese patients have been simulated both on
“normal weight” phantom and on “obese phantoms” to analyze organ dose
differences.
EX and ID can simulate tube current modulation (TCM): the effect on organ
dose has been evaluated comparing a chest-abdomen-pelvis scan simu-
lated with constant current and one with TCM.
Results: Dose variability of 30% has been found for totally included organs
of “standard male and female” phantoms due to different dimension and
position of organs. Variability increases for partially included organs up to
70%.
Scan parameters of an obese patient simulated on an “obese phantom”
results in, at least 10% less organ dose than if simulated on a “normal weight
phantom”, with percentage increasing with obesity degree.
Finally, organ doses estimated with and without TCM can vary up to 40%.
Conclusion: A precise patient dose estimate is difficult to obtain, also
because phantoms are eventually just a representation of the patient’s
anatomy and the actual scanner can differ from the one used by software.
Nevertheless, a comparison between different SW can help understand the
existing error bars across dose estimates for further improvement.
B.278
HEALTH DOSE ASSESSMENT OR HEALTH TECHNOLOGY ASSESSMENT?
L. Manco *, A. Turra. Medical Physics Unit, Arcispedale S.Anna Hospital, Ferrara,
Italy
Introduction: The diffusion of radiation dose management software (DMS)
nationwide should allow dose-population’s monitoring? The use of
DoseWatch (GE) software during the two past years allows a continuous
monitoring of CT dose at Sant’Anna Hospital in Ferrara. The purpose of this
work is to evaluate the effective reduction of CT dose after installation of
iterative reconstruction method (ASiR, GE).
Materials and Methods: More than 30,000 exams were collected on
DoseWatch from two CT scanners GE Lightspeed VTC 32 slice. One is used
for body exams and the other for neuro ones. The analysis was carried out
comparing DLP values before and after installation of ASiR in different study
protocols.
Results: The use of iterative reconstruction method on CT scanners allows
a reduction of average dose of 25% for protocol thorax-abdomen and 30%
for protocol head. The compare between before and after ASiR, on all exams,
shows a dose reduction of 52% on CT Boby and 30% on CT Neuro.
e82 Abstracts/Physica Medica 32 (2016) e71–e96