Radiant energy – Calibration or standardization methods
Reexamination Certificate
1998-12-11
2001-02-27
Hannaher, Constantine (Department: 2878)
Radiant energy
Calibration or standardization methods
C250S374000, C250S375000, C250S370080, C250S370060, C250S370100, C250S370110, C250S371000
Reexamination Certificate
active
06194714
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods of processing autoradiography images (autoradiography as such in beta radiation, scintigraphy in gamma radiation etc.), i.e. to methods which make it possible to obtain at least one image from radioactive radiation emitted by at least one radioactive tracer contained in a substrate.
BACKGROUND OF THE INVENTION
More particularly the invention relates to a method of generating at least one image of a substrate from radioactive radiation coming from a number I at least equal to 2 radioactive sources, these radioactive sources comprising at least one radioactive tracer contained in the substrate, this method comprising the following stages:
a) the radioactive radiation emitted by the substrate is detected in a certain observation field sub-divided into K×L pixels, by means of a detector which generates for each pixel (x
k
,y
1
) of the observation field a detection signal f (x
k
,y
1
) representing the detection or non-detection of a radioactive emission in this pixel,
b) and the data representing the different detection signals generated by the detector are memorised, individually for each radioactive emission detected during a determined period called the observation period, these memorised data corresponding at least to an estimated position of an emission point of radioactive radiation in the substrate.
The use has already been suggested of a method of this type for generating, using an apparatus for imaging with a solid scintillator (marketed under the trade name “&mgr;-imager” by the company BIOSPACE MESURES, Paris, France), two images corresponding respectively to the distribution in the substrate of two different tracers (
35
S and
32
P) emitting radiation with different energy spectra; by using separation criteria of these emissions (such as the number of pixels affected by a detection, the maximum amplitude of the detection signal for a detection, the sum of the amplitudes of the detection signals for the same detection, etc.), each detection is classified more or less in real time as corresponding either to one tracer, or to the other (see the thesis of P. Laniece: “Quantization in hybridization in situ and in autoradiography: development of a high resolution radio-imager”, Institut de Physique Nucléaire, 1992 and Y. Charon: “Radio-imaging and biology”, thesis of the UniversitéDenis Diderot,—Paris VII, 1995). In this case, the emission point of each radiation detected is likewise estimated, more or less in real time, at the same time as this radiation is attributed to one or the other of the tracers, and each of the images finally generated consists simply in the superposition of the estimated emission points of the different radiation detected, respectively for each tracer.
OBJECTS AND SUMMARY OF THE INVENTION
The purpose of the present invention is particularly to perfect the known methods of the above-mentioned type in order to improve the definition of the image. To this end, according to the invention, a method of the type in question is essentially characterised in that the data memorised during the period of observation additionnally correspond to a number q at least equal to 1 of supplementary numerical parameters A
1
. . . Aq relative to the detection signals generated by each detection of radioactive radiation, each of these parameters, called “criteria”, being able to take a non-zero number of values A
1
l
. . . to A
1
jl
, . . . , Aq
1
. . . Aq
jq
, called “characteristics”, in that before the observation period (a single time only, at regular time intervals, or before each new observation period or series of observation periods), a preliminary calibration stage is implemented, in which an impulse response is measured Ri,j
1
, . . . jq(x,y) of the detector for each radioactive source i and for each possible combination of the characteristics A
1
j1
, . . . ,Aq
jq
of the different criteria A
1
. . . Aq, this impulse response corresponding to a probability that, when the detector receives radiation coming from a point source of the aforementioned radioactive source, said detector generates on the pixels of the observation field having the relative coordinates (x,y) in relation to the point source, a detection signal presenting said combination of characteristics, and in that said method comprises the following supplementary stages:
c) from the set of memorised data, determining a distribution H(x
k
,y
1
, A
1
j1
, . . . , Aq
jq
) of the detections corresponding to these data, corresponding to the number of detections at each estimated emission point of coordinates (x
k
, y
1
) with each combination A
1
j1
, . . . , Aq
jq
of the characteristics of the different criteria,
d) and estimating a distribution h′i(xk,yl) of detections corresponding to each radioactive source i, which minimises the respective deviations between the distribution H(x
k
, y
1
, A
j1
, . . . ,A
jq
) and the corresponding values:
H
′
(
xk
,
yl
,
A1
,
j1
,
…
Aqjq
)
=
∑
i
h
′
i
(
xk
,
yl
)
⊗
Ri
,
j1
,
…
jq
(
x
,
y
)
,
where
:
h
′
i
(
xk
,
yl
)
⊗
Ri
,
j1
,
…
jq
(
x
,
y
)
=
∑
m
∑
n
h
′
i
(
xk
,
yl
)
.
Ri
,
j1
,
…
jq
(
xk
–
xm
,
yl–yn
)
,
i being an integer between 1 and I, and referring to the radioactive source being considered,
j1 being an integer between 1 and J1, referring to the j1st characteristic possible for the criterion no. 1,
. . .
jq being an integer between 1 and Jq referring to the jq
th
characteristic possible for the criterion no. q,
m being an index between 1 and L,
n being an index between 1 and K,
the distributions h′i(xk,yl) corresponding, for each radioactive source i constituted by a tracer contained in the substrate, to the image of the distribution of this tracer in said substrate.
Thanks to these arrangements, all the information contained in the history of the detections carried out during the observation period is taken into account, in order to obtain an image with excellent resolution.
In preferred embodiments of the invention, one can possibly have recourse in addition to one or other of the following arrangements:
the radioactive sources comprise a plurality of tracers, to which as many distributions h′i(xk,yl) correspond, each forming the image of the distribution of one of said tracers in the substrate;
one of the radioactive sources is a background radiation;
at least one of the radioactive sources is an imaginary source corresponding to at least one defect of the detector;
the detector is a gas detector in which the gamma radiation generates avalanches of electrons on the basis of the detection signal, and said detector comprising hot spots constituted by spots in which are generated avalanches of electrons without detection of beta radiation, these hot spots constituting the imaginary source mentioned above;
each distribution h′i(xk,yl) is estimated by minimising an error function Er defined by:
Er
=
∑
j1
λ
j1
…
∑
jq
λ
jq
∑
k
∑
l
[
H
(
x
k
,
y
l
,
A1
j1
,
…
,
Aq
jq
)
-
∑
i
h
′
i
(
x
k
,
y
l
)
⊗
R
i
,
j1
,
…
jq
(
x
,
y
)
]
2
where &lgr;
j1
. . . &lgr;
jq
are weighting indices:
the indices &lgr;
j1
. . . &lgr;
jq
are all equal to 1;
at least one of the criteria is chosen from the group consisting in:
the maximum amplitude of the detection signal, for each detection,
the number of pixels affected by each detection, these pixels forming a whole which is called hereinafter “detection spot”,
the ellipticity of the detection spot,
the sum of the values of the signal detection on the detection spot,
the variance of the detection spot,
the narrowness of the detection spot,
the asymmetry of the det
Hennion Claude
Maitrejean Serge
Sandkamp Bernhard
Biospace Instruments
Gagliardi Albert
Hannaher Constantine
Larson & Taylor
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