X-ray or gamma ray systems or devices – Electronic circuit – With display or signaling
Reexamination Certificate
2000-10-10
2001-06-12
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Electronic circuit
With display or signaling
C378S098110
Reexamination Certificate
active
06246747
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
BACKGROUND OF THE INVENTION
This invention relates generally to multi-energy x-ray machines and in particular to an improved method of discriminating between x-ray energies in such machines that permit lower x-ray flux rates and longer x-ray tube life.
Measuring the x-ray attenuation of an object at two different x-ray energies can reveal the composition of that object as a proportion of two arbitrarily selected basis materials. In the medical area, the basis materials may be “bone” and “soft tissue” allowing x-ray images to yield quantitative information about in vivo bone density for the diagnosis of osteoporosis. Alternatively, the basis “fat” and “lean” tissue may be selected to provide the indication of total body fat useful in the treatment of obesity or conversely wasting diseases.
Basis materials of “explosive” and “nonexplosive” materials may be used in the baggage scanning industry to augment images of the contents of baggage with the indication of the composition of the imaged contents.
Other basis materials may be selected for other industrial applications.
Referring to
FIG. 1
, a commercially available multi-energy x-ray machine
10
, in this case a bone densitometer, includes an x-ray source
12
supported at one end of a C-arm
14
positioned beneath a patient support table
16
. An energy sensitive detector
18
is held by the other end of the C-arm
14
opposite the x-ray source receives a fan beam
20
of x-rays from the x-ray source
12
. The fan beam is formed by a collimator (not shown) being one or more x-ray opaque shutters which block x-rays in all but narrow rectangular cross section as is well understood in the art.
A patient (not shown) positioned on the patient support table
16
may be scanned by motion of the C-arm with respect to the patient so that the x-ray fan beam
20
illuminates the patient over a region of interest.
Referring now to
FIG. 2
, the x-ray source
12
may be a conventional polychromatic x-ray tube producing x-rays having a single mode spectrum
22
encompassing both high and low energy x-rays. The x-ray fan beam
20
is received by a k-edge filter
24
such as a cerium filter having an a real density of approximately 343 mg/cm
2
. The effect of the k-edge filter
24
is to preferentially block mid-energy x-rays to produce a bi-modal spectrum
26
having two peaks in regions of high and low energy.
The x-ray fan beam
20
continues through a patient
28
to arrive at an energy sensitive detector
18
. Absorption of x-rays by the patient
28
produces at the energy sensitive detector
18
an attenuated bi-modal spectrum
30
also exhibiting the two peaks of bi-modal spectrum
26
but with lower amplitude.
The energy sensitive detector
18
may include a single scanned detector element or a number of detector elements
32
arranged in a linear or a real array. The detector elements in combination with motion of the C-arm (shown in
FIG. 1
) allow a spatial mapping of x-ray signals to particular lines through the patient
28
and thus imaging of the patient
28
and spatially dependent measurements of the patient
28
such as area densities.
A detector is “energy sensitive” as used herein if it can distinguish the fluence of x-rays at different energies. A number of energy discriminating detector types are known in the art including scintillation-type detectors in which the x-rays are converted to light via a scintillator material. The amount of light for each event indicates the energy of the x-ray photon. The scintillation material may be followed by a photo multiplier tube to amplify the light output and the light may be measured by any of a number of light detectors including but not limited to Charge-Coupled Devices (CCD). Ionization detectors which work by measuring current formed by an ionized gas in the path of the x-rays can provide energy discrimination through measurement of the amount of current generated at each photon event. Solid state detectors using photodiodes can provide energy discrimination through the use of filters in a stacked or side-by-side configuration. Cadmium Zinc Telluride (CZT) provides direct electrical outputs in response to detected x-rays in the form of pulses for each incident photon where pulse amplitude or area is proportional to the photon's energy.
As shown in
FIG. 2
, the output of the energy sensitive detector
18
for one detector element
32
may be a series of pulses
34
of varying times and heights corresponding to arrival times of related x-ray photons and the energies of those photons. The statistical distribution of the heights of the pulses
34
will conform generally to the attenuated bi-modal spectrum
30
.
The signals for each detector element
32
may be received by an amplifier/pulse shaping circuit
35
and then by energy discriminator
36
(only one shown for clarity). The energy discriminator compares each pulse's height to a reference band
38
(implemented by a high and low voltage) which establish a high and low end point of an energy range for a plurality of window comparators
40
(
a
) through
40
(
c
). Generally, only pulses having heights within the corresponding reference band
38
will be passed by the window comparators
40
(i.e., pulse voltage peaks greater than the low voltage and lesser than the high voltage). Window comparators
40
can be constructed by two standard comparators, the first connected to the low references voltage and the pulse signal to provide a low output unless the pulse is above the low reference voltage and the second connected to the high references voltage and the pulse signal to provide a low output unless the pulse is below the high reference voltage. The outputs of the comparators are then logically ANDed together.
Referring now to
FIGS. 2 and 4
, each reference band
38
(
a
)-(
c
) generally establishes a different detection zone in the attenuated bi-modal spectrum
30
. Reference band
38
(
c
) in conjunction with window comparator
40
(
c
) defines a low energy (LE) range causing the detection of only x-ray photons in the lower peak of attenuated bi-modal spectrum
30
. Similarly, ranges
38
(
a
) and
38
(
b
) together, establish with their window comparators
40
(
a
) and
40
(
b
), a high-energy (HE) range detecting photons in the higher energy peak of attenuated bi-modal spectrum
30
. Within the HE range, reference band
38
(
b
) further establishes a lower range (LR) and reference band
38
(
a
) establishes an upper range (UR) equally dividing the HE range. The purpose of these subranges will be described below.
Each window comparator
40
(
a
) through
40
(
c
) is followed by an integrator
42
such as a counter which counts the total number of pulses passed by the comparator within the respective ranges LE and HE and subranges LR and UR of range HE.
The output of the integrators
42
is provided to a basis material processor
46
acting on high and low energy attenuation information to establish the composition of the intervening material of the patient
28
. The low energy attenuation information is provided directly by the output of the integrator associated with window comparator
40
c
of the LE range whereas the LR and UR images are added together to form the high energy attenuation information of the HE range. The latter addition is shown by summing block
44
.
The basis material processor
46
operates according to well known techniques to process the high and low energy attenuation information to determine a basis material decomposition such as may be displayed to an operator on an interface terminal
48
of conventional design. The basis material processor
46
may be a microprocessor-based computer of a type well known in the art.
Referring now to
FIG. 4
, variations in the signal chain between the detector elements
32
and the integrators
42
can cause the attenuated bi-modal spectrum
30
to vary in time by a compression or dilation along the horizontal or energy axis as indicated by attenuated bi-modal spectrum
30
′. For
Lenz Daniel R.
Payne Randall K.
Washenko Robert A.
Wear James A.
GE Lunar Corporation
Ho Allen C.
Kim Robert H.
Quarles & Brady LLP
LandOfFree
Multi-energy x-ray machine with reduced tube loading does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Multi-energy x-ray machine with reduced tube loading, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multi-energy x-ray machine with reduced tube loading will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2463823