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

Results:

T2 Reference values were found between 13 and 150 ms. The mean

percentage difference between T2 reference and GRASE values was 16%.

In vivo brain T2 values ranged from 80 to 120 ms. The Bland–Altman plot

showed a positive trend, possibly indicating that the differences from the

two calculation methods tend to get larger as the average increase.

Conclusions:

A number of recent studies reported that brain iron content

can be assessed by T2 measurements. GRASE is a relatively new technique

with the potential to calculate brain volumetric T2 values. However, to the

best of our knowledge, its accuracy has never been tested. We believe that

the accuracy in calculating in vivo T2 values is essential in studies aiming

to assess brain diseases. In our experience, the use of T2 values evaluated

using proprietaryMR software is not recommended in quantitative evaluation.

http://dx.doi.org/10.1016/j.ejmp.2016.01.437

E.429

QUALITY ASSURANCE OF PHASED ARRAY COILS: ANALYSIS OF THE NOISE

AMPLIFICATION FACTOR DISTRIBUTION

A. Coniglio

* , a ,

G. Vilches Freixas

b , c ,

A. Santarelli

a ,

M. Ciocca

c ,

L. Begnozz

i a .

Medical Physics Department, S. Giovanni Calibita Fatebenefratelli Hospital,

Roma, Italy;

Universitè de Lyon, CREATIS, CNRS, UMR5220, Inserm U1044,

INSA-Lyon, France;

Medical Physics Unit, CNAO Foundation, Pavia, Italy

Introduction:

Due to the spatially varying noise across the image and the

noise dependence on the geometry coil inherent to parallel imaging (PI)

methods, conventional signal to noise ratio (SNR) measurements are in-

adequate to test the performance of phased array (PA) coils working with

PI. The aim of this work is to provide a quality assurance protocol for PA

coils working with PI based on the analysis of the noise amplification factor

(g-factor) distribution.

Materials and Methods:

A fast gradient echo sequence was optimized to

calculate pixel-based SNR and g-factor maps using 3 different reduction

factors (R). Acquisitions were performed using both sensitivity encoding

(SENSE) and generalized auto-calibrating partially parallel acquisition

(GRAPPA) algorithms. Over a period of 18 months, data were acquired with

1.5 T and 3 T MR systems using PA head coils with 8 and 32 channels, re-

spectively. A custom Matlab® code was developed to generate SNR and

g-factor maps. A three-parameter (a,b, k) log-logistic distribution was used

to fit the g-factor distribution. Mean baseline values with the correspond-

ing standard deviations were calculated for mean g-value, distribution

parameters and SNR, with the latter evaluated according to the AAPM pro-

tocol. Acquisitions with different coil operation modes were performed.

Results:

Reduction factors of 3 and 4 resulted in more efficient discrimi-

nation between different coil operation modes. In a number of situations,

SNR lay within the baseline interval whereas a and k parameters lay outside:

image reconstruction with 7 of 8 channels (SENSE,R

3), acquisition per-

formed with dual-MCM (GRAPPA,R

4) and with RSM separate operation

mode (GRAPPA,R

3).

Conclusions:

The analysis of the g-factor distribution permitted to distin-

guish different coil operation modes with respect to the conventional SNR

calculation method and mere calculation of the mean g-factor. The pro-

posed approach appeared robust for both MR systems and for two different

PI algorithms.

http://dx.doi.org/10.1016/j.ejmp.2016.01.438

E.430

IMPLEMENTING INTRA-OPERATIVE MAGNETIC RESONANCE IMAGING

EQUIPMENT – SAFETY CONCERNS

F. Cretti

* , a ,

M. Branchi

a ,

G. Manni

a ,

S. Canini

a ,

F. Biroli

a ,

G. Bonaldi

a ,

C. Bernucci

a ,

M. Passon

i a ,

R. Suard

i a ,

F. Campanella

b ,

P. Colomb

o c .

Azienda

Ospedaliera Papa Giovanni XXIII, Bergamo, Italy;

INAIL Area Ricerca

Certificazione Verifica, Roma, Italy;

Azienda Ospedaliera Niguarda Ca’ Granda,

Milano, Italy

Introduction:

Intraoperative MRI represents an evolution of

neuronavigational tools, addressing the goal of accurate targeting of the

region of interest, with the advantage of overcoming problematic discrep-

ancy in the imaged anatomy after opening the cranium. Nevertheless, taking

a MRI scanner to the surgery theater is not a straightforward operation,

due to severe safety constraints. In our institution a

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solution

was adopted, consisting in a moving 1.5 T scanner that can work in two

different positions, in a two-room layout. One position is dedicated to di-

agnostic activity whereas the other one is for intraoperative use exclusively.

The two rooms are separated by a sliding door, kept close during diagnos-

tic activity – in that case the surgery room can work independently – and

open during intraoperative use, when the two rooms are an open space,

with the scanner set in the surgery position. This abstract reports prelim-

inary steps accomplished to get local authority approval.

Material and Methods

: A multidisciplinary team worked to get a project

solution compliant with safety standard. Topics concerned both technical

aspects (aeraulic system, dynamic quench system, Faraday cage continu-

ity, emergency devices, static magnetic field shielding, magnetic

compatibility with the underneath 3T magnet room), and organization

aspects, involving site regulations, staff education, patient management,

surgical devices labeling and administration. Also, INAIL consultation was

availed, with significant contribution to project development.

Results:

A satisfying safety strategy was finally achieved. Also, a specific

surgery procedure was written – as an integrant part of the safety rules –

in order to insure adequate preparation of both patient and surgery area

before scanner positioning. Now the system is being installed.

Conclusion:

Given the complexity of the project, multidisciplinary work

is a prerequisite for successful and safe implementation and operating.

http://dx.doi.org/10.1016/j.ejmp.2016.01.439

E.431

TEMPORAL STABILITY QA IN FUNCTIONAL MAGNETIC RESONANCE

IMAGING

L. Fedeli *, S. Busoni, M. Fedi, P. Saletti, A. Taddeucci.

Azienda Ospedaliero

Universitaria Careggi, Firenze, Italy

Introduction:

MRI scanner performance temporal stability in functional

magnetic resonance imaging (fMRI) is a fundamental aspect both in lon-

gitudinal and cross sectional studies, due to the fact that the blood oxygen

level dependent (BOLD) effects are of the order of few percent. A revised

version of Friedman protocol (JMRI, 23–2006) was adopted to check the

stability of scanners on a weekly basis. Results of a two year survey of four

1.5 T MRI clinical scanners are reported.

Materials and Methods:

The purpose of the procedure is to measure the

stability of the scanners in conditions that are as similar as possible to the

clinical settings. The same head coil and scanning sequence used in the fMRI

experiments are employed. A time series of 200 images of the QA vendor

phantom is collected, with an overall acquisition time of 15 minutes. The

automated analysis is performed with a home-made software code and pro-

vides information about signal intensity, uniformity, magnitude spectrum,

radius of decorrelation, SNR and signal fluctuation to noise ratio.

Results:

All four 1.5 T MRI scanner data fluctuations are of the order of a

few per cent, showing a suitable stability over the two year survey. It appears

that there is a correlation between SNR and SFNR (r

0.7). The Fourier anal-

ysis does not show periodic noise.

Conclusions:

Regular check of parameter stability provides a strong feed-

back regarding scanner performances, and may allow predicting possible

malfunction. Acquired data may be used in order to assess scanner per-

formance reference levels.

http://dx.doi.org/10.1016/j.ejmp.2016.01.440

E.432

SAFETY FOR MRI PATIENTS WITH IMPLANTED MEDICAL DEVICES

E. Genovese

* , a ,

A. Napolitano

a ,

S. Donatiello

a ,

C. Orlandi

a ,

P. Toma’

b ,

F. Campanella

c ,

G. Calcagnin

i d ,

F. Censi

d .

Enterprise Risk Management/

Medical Physics, Bambino Gesù Children’s Hospital, IRCCS, Rome, Italy;

Department of Imaging, Bambino Gesù Children’s Hospital, IRCCS, Rome, Italy;

Dipartimento Medicina, Epidemiologia, igiene del lavoro ed ambientale, INAIL,

Rome, Italy;

Dip. Tecnologie e Salute, Istituto Superiore di Sanità, Rome, Italy

Introduction:

Thanks to the high diagnostic power of magnetic reso-

nance scanners, there is a steady increasing in the number of patients

undergoing magnetic resonance exams while having an implanted medical

device. At the same time, even though a few old regulatory burdens within

the Italian law have been recognized as partially outmoded and misguided

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Abstracts/Physica Medica 32 (2016) e124–e134