System for non-invasive classification of different types of micro-calcifications in human tissue
A non-invasive method distinguishes between two types of micro-calcification by x-ray imaging in mammography. Two major types of micro-calcifications are found and confirmed by histopathology and they are correlated to benign and malignant breast lesions. Distinguishing between them non-invasively will significantly improve early breast cancer diagnosis. This is based on the fact that these two types of micro-calcifications show opposite absorption and small-angle scattering signals in x-ray imaging. The imaging system, which can record these two signals of the breast tissue simultaneously for instance, an x-ray grating interferometer, can be used to uniquely determine the micro-calcification type. This is expected to be used in mammography to improve early breast cancer diagnosis, increase diagnosis accuracy and decrease the biopsy rate.
1. A system for a non-invasive classification of different types of micro-calcifications in human tissue by combining an absorption signal and a small-angle scattering signal, the system comprising:
a set-up for recording the absorption signal and the small-angle scattering signal; and
signal processing means configured to analyze at least one pair of micro-calcifications, an analysis based on different types of micro-calcifications having opposite absorption and small angle scattering signals, wherein, one type gives a weaker absorption signal but a stronger small-angle scattering signal than the other type or vice-versa.
2. The system according to claim 1 ,
wherein a signal pair (t 1 ,t 2 ) is assigned to a pair of micro-calcifications, where t 1 ,t 2 ⊂{+,−} and t 1 and t 2 represent a relative signal strength of the absorption signal and the small angle scattering signal, respectively, wherein “+” means a signal is stronger, “−” means the signals is weaker; and
further comprising an evaluator module disposed in said signal processing means for identifying if two signal pairs constitute a combination of (+,−) and (−,+), which yields that the two signal pairs belong to different types of micro-calcifications wherein a micro-calcification signed to (−,+) is determined to be more likely a type I micro-calcification whereas (+,−) indicates that the micro-calcification is determined to be more likely a type II micro-calcification.
3. The system according to claim 1 , wherein said signal processing means calculates a ratio r of the absorption signal and the small-angle scattering signal of the micro-calcification to decouple a thickness parameter and identify micro-calcification types I and II, wherein
r
=
AC
SC
=
μ
_
·
L
c
S
_
·
L
=
μ
_
c
S
_
,
where
AC is the absorption signal, AC=∫ 0 L μ(l)dl= μ ·L;
SC is the small-angle scattering signal, SC=c∫ 0 L S(l)dl=cS·L;
L is a thickness of a specimen;
μ is an attenuation coefficient;
S is a generalized scattering parameter;
c is a constant decided by geometry and system parameters of said set-up; and
further using an predetermined threshold t that will sort out if,
{
r
<
t
,
one
type
of
the
micro
-
calcification
r
>
t
,
another
type
of
the
micro
-
calcification
.
4. The system according to claim 3 , wherein when signal data is obtained with multi-modality computed tomography, said signal processing means reconstructs tomograms of absorption information and small-angle scattering information from projection and the attenuation coefficient μ and the generalized scattering parameter S are obtained directly, wherein the absorption information and the small-angle scattering information are also opposite for two types of the micro-calcifications.
5. The system according to claim 1 , wherein the absorption signal and small-angle scattering signal are obtained from a configuration outputting x-rays, for obtaining quantitative x-ray images from a sample, said configuration including:
an X-ray source;
said setup having at least two gratings;
a position-sensitive detector with spatially modulated detection sensitivity having a number of individual pixels;
means for recording images of said position-sensitive detector;
said signal processing means having an evaluator module enabled to evaluate intensities for each pixel in a series of the images, in order to identify characteristics of an object for each individual pixel as an absorption dominated pixel, a differential phase contrast dominated pixel or an x-ray scattering dominated pixel; and
wherein the series of the images is collected by continuously or stepwise rotating from 0 to πor 2π either a sample or said setup and said x-ray source relative to the sample.
6. The system according to claim 5 , wherein the system performs in a so-called “near field regime” or in a “Talbot-regime”.
7. The system according to claim 5 , wherein said gratings include:
a first line grating selected from the group consisting of absorption gratings and phase gratings and is a low absorption grating generating a considerable X-ray phase shift; and
a second line grating having a high X-ray absorption contrast with its period being a same as that of a self image of said first line grating; and
said second line grating is disposed closely in front of said position-sensitive detector with its lines parallel to those of said first line grating.
8. The system according to claim 7 , wherein for near-field-regime operation, a distance between said gratings is chosen freely within the near field regime, and for the Talbot-regime is chosen according to
D
n
,
sph
=
L
·
D
n
L
-
D
n
=
L
·
n
·
p
1
2
/
2
η
2
λ
L
-
n
·
p
1
2
/
2
η
2
λ
where n=1,3,5 . . . , and
η
=
{
1
if
the
phase
shift
of
G
1
is
(
2
l
-
1
)
π
2
,
p
2
=
L
+
D
n
,
psh
L
p
1
2
if
the
phase
shift
of
G
1
is
(
2
l
-
1
)
π
,
p
2
=
L
+
D
n
,
psh
L
p
1
2
where l=1,2,3 . . . , D n is an odd fractional Talbot distance when a parallel X-ray beam is used, while D n,sph is that when a fan or cone X-ray beam is used, L is a distance between said x-ray source and said first line grating, and G 1 is said first line grating.
9. The system according to claim 5 , wherein said at least two gratings are two of three gratings, and phase stepping is performed by a shift of one of said three gratings with respect to said other gratings.
10. The system according to claim 1 , wherein said set-up for recording the absorption signal and the small-angle scattering signal records signals of X-ray investigations based on grating-based interferometry, based on analyzer-crystal-based imaging or based on coded aperture imaging.
11. The system according to claim 5 , wherein the absorption signal and the small-angle scattering signal are obtained from a configuration outputting hard x-rays.
12. The system according to claim 7 , wherein the considerable X-ray phase shift being of π or odd multiples thereof.