Hand-held gamma camera

Details Hand-held gamma camera Hand-held gamma camera

2003-04-22

2004-04-20

Hannaher, Constantine (Department: 2878)

Radiant energy

Invisible radiant energy responsive electric signalling

C250S370010, C250S36100C

Reexamination Certificate

active

06723988

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to hand-held gamma cameras and in particular to a hand-held gamma camera with a remotely readable spatial position measurement.
BACKGROUND OF THE INVENTION
Generally, in nuclear imaging, a radioactive isotope is injected to, inhaled by or ingested by a patient. The isotope, provided as known as a radioactive-labeled pharmaceutical (radio-pharmaceutical) is chosen based on bio-kinetic properties that cause preferential uptake by different tissues. The gamma or beta photons emitted by the radio-pharmaceutical are detected by radiation detectors outside the body, giving its spatial uptake distribution within the body, with little trauma to the patient.
FIG. 1
illustrates a general nuclear-imaging detector
10
comprising a NaI(Tl) scintillation crystal
12
. Generally, scintillation crystal
12
, of a diameter D
1
, is large enough to image a significant part of the human body (typically 40 cm). An array of photo-multiplier tubes (PMTs)
14
view scintillation crystal
12
, to give positional sensitivity. Each PMT
14
has an x and a y coordinate. When a photon is absorbed by scintillation crystal
12
, light is generated. A number of PMTs
14
receive the light and produce signals. The X and Y coordinates of the event are determined by the strength of the signals generated by each PMT. The energy of the event is proportional to the sum of the signals, called the Z signal. Only Z signals within a given range are counted.
Size is a basic drawback of the multiple PMTs detector system. The basic limiting size of a PMT is too large for multiple PMTs to be fitted in a small camera. An alternative system using an Nal(Tl) scintillation crystal, backed by a single, position sensitive PMT, can be substantially smaller, but the field of view is small.
Semiconductors with high atomic numbers and relatively high densities such as CdZnTe, CdTe, HgI
2
, InSb, Ge, GaAs, Si, PbCs, PbCs, PbS, or GaAlAs, have a high stopping power and can be used as gamma ray detectors with good photon detection efficiencies, good spatial resolution, and a relatively high photon-energy resolution. Solid state semiconductor gamma cameras generally comprise arrays of pixelated detector, hereinafter referred to as “pixelated detectors”. One type of pixelated detector is described in PCT publication WO 98/23974, the disclosure of which is incorporated herein by reference.
FIG. 2
shows a typical construction of a pixelated detector
20
comprising a crystal
22
formed from a semiconductor material such as one of those noted above. A face
24
of crystal
22
has a large single cathode electrode
26
. An opposite face
28
of crystal
22
has an anode
30
comprising a rectangular array of identical small square anode pixels
32
. Typically, sizes of anode pixels
32
vary between 1 and 4 mm
2
, and the thickness of crystal
22
, between anode
30
and cathode
26
is on the order of millimeters to a centimeter. In operation, a voltage difference is applied between anode and cathode so that an electric field, hereinafter referred to as a “detector field”, is generated in crystal
22
. This field is typically on the order of a few kilovolts per centimeter.
When a photon, having an energy typical of the energies of photons used in gamma cameras, is incident on crystal
22
, it generally loses all its energy in crystal
22
by ionization and produces pairs of mobile electrons and holes in a localized region of crystal
22
. As a result of the detector field, the holes drift to cathode
26
and the electrons drift to anode
30
, thereby inducing charges on anode pixels
32
and cathode
26
. The induced charges on anode pixels
32
are sensed and generally partially processed by appropriate electronic circuits located in a detector base
34
to which detector
20
is mounted. Signals from the induced charges on pixels
32
are used to determine the time at which a photon is detected, how much energy the detected photon deposited in the crystal and where in the crystal the photon interaction took place.
An alternative solid-state detector system is described in U.S. Pat. No. 4,672,207 “Readout System for Multi-Crystal Gamma Cameras” by Derenzo. The detector system comprises an array of scintillation crystals arranged in N rows and M columns and adapted to be struck by gamma rays from a subject. A separate solid-state photodetector is optically coupled to each crystal. N+M amplifiers, connected to the photodetectors distinguish the particular row and column of an activated photodetector.
Another alternative solid state system comprises a single scintillation crystal, optically coupled to multiple photodetectors, wherein each photodetectors has a specific x, and y coordinate.
Generally, a collimator
16
is placed between scintillation crystal
12
or
22
and the tissue. Commonly, collimator
16
is honeycomb shaped, comprising a large number of holes separated by parallel lead septa. The purpose of collimator
16
is to intercept and eliminate gamma-ray photons that are not traveling in an accepted direction, parallel to the lead septa.
Small gamma cameras that are hand-held are known. Generally, they are based on solid-state detectors such as a pixelated detector. Alternatively, they comprises a single NaI(Tl) scintillation crystal and a single, position sensitive PMT.
Small cameras are especially useful for detecting beta radiation. Since beta rays are strongly absorbed by tissues, small cameras are able to reduce the distance between the radiation source and the camera, especially in the operating room.
A specific problem with hand-held garnrna cameras is spatial location of any suspected finding with respect to some known reference system, since the hand-held camera itself is not referenced to any coordinate system.
New radio pharmaceuticals enhance the need for mini-cameras for both beta and gamma radiation. These radio pharmaceuticals are based on peptides, FABs (fraction of antibody) or MAB (monoclonal antibodies) which are especially designed to attach themselves to receptors usually found in specific cancerous cells.
SUMMARY OF THE INVENTION
One aspect of some preferred embodiments of the present invention relates to providing a small radiation camera such as a gamma camera or beta camera with a preferably remotely readable spatial coordinate determining device that registers the coordinates of the camera, Preferably, the six orthogonal position and orientation coordinates. Preferably, the remote spatial coordinate device comprises two parts:
1. a transmitter which is attached to the camera, for example at the tip of the handle, and which transmits 3-D coordinate information, preferably continuously, during operation; and
2. a receiver at some remote location to the camera, for example on the ceiling, or near a data-acquisition computer, which receives the 3-D coordinate information sent by the transmitter.
In some preferred embodiments of this aspect, the remote spatial coordinate device is an optical device. Alternatively, it is based on radio positioning. Alternatively, it is a GPS like device (together with some means for measuring angles). Alternatively, it is based on microwaves. Alternatively coordinate determination is based on measurements of static, pulsed DC or AC magnetic fields. Alternatively, any remote spatial coordinate determining device known in the art. None of the above techniques or devices are new, per se, and therefore will not be discussed in detail herein. Many such devices are known in the art, and the present invention may utilize any suitable device.
In some preferred embodiments of this aspect, the remotely readable spatial coordinate determining device is connected to a data-acquisition computer and a display screen, preferably by a cable, so that information acquired by the gamma camera is displayed on screen in real time, with the spatial coordinates of any lesion. Alternatively, signals related to the coordinate determination may be carried by the same cable. Alternatively, both data and coordinate information m

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