Detector for nuclear imaging

Details Detector for nuclear imaging Detector for nuclear imaging

1998-12-07

2002-03-19

Hannaher, Constantine (Department: 2878)

Radiant energy

Invisible radiant energy responsive electric signalling

With or including a luminophor

C250S360100, C250S370090

Reexamination Certificate

active

06359279

ABSTRACT:

BACKGROUND
The present invention relates to the art of diagnostic imaging. It finds particular application in conjunction with nuclear or gamma cameras and single photon emission computed tomography (SPECT) and will be described with particular reference thereto. It is to be appreciated, however, that the present invention will also find application in other non-invasive investigation techniques and imaging systems such as single photon planar imaging, whole body nuclear scans, positron emission tomography (PET) and other diagnostic modes.
In diagnostic nuclear imaging, one or more radiation detectors are mounted on a movable gantry to view an examination region which receives a subject therein. Typically, one or more radiopharmaceuticals or radioisotopes such as
99m
Tc or
18
F-Fluorodeoxyglucose (FDG) capable of generating emission radiation are introduced into the subject. The radioisotope preferably travels to an organ of interest whose image is to be produced. The detectors scan the subject along a selected path or scanning trajectory and radiation events are detected on each detector.
In a traditional scintillation detector, the detector includes a scintillation crystal that is viewed by an array of photomultiplier tubes. A collimator which includes a grid- or honeycomb-like array of radiation absorbent material is located between the scintillation crystal and limits the angle of acceptance of radiation which will be received by the scintillation crystal. The relative outputs of the photomultiplier tubes are processed and corrected to generate an output signal indicative of the position and energy of the detected radiation. The radiation data is then reconstructed into an image representation of a region of interest.
A so-called rotating laminar radionuclide camera (“ROLEC”) has been disclosed by Tosswill and others. Devices utilizing a cadmium telluride (CdTe) detector arrangement have been disclosed in Mauderli, et al., A Computerized Rotating Laminar Radionuclide Camera, J. Nucl. Med 20: 341-344 (1979) and Entine, et al., Cadmium Telluride Gamma Camera, IEEE Transactions on Nuclear Science, Vol. NS-26, No. 1: 552-558 (1979). According to one version, the device included a linear array of CdTe detectors separated by tungsten plates that confined the field of view of each detector to one dimension. The device had a square (approximately 4 cm×4 cm) active area, although a circular lead mask reduced the active area to 13.2 cm
2
. The detectors, which had platinum-film electrodes, were attached to copper strips on a printed circuit board that also served as the base of the collimator and as a support for amplifier-discriminator circuits.
A ROLEC having a 250 mm×250 mm active area was disclosed in Tosswill, U.S. Pat. No. 4,090,080, issued May 16, 1978 and entitled Imaging. The device included scintillating plastic sheets disposed between parallel collimator plates supported by a steel frame. Fiber optics epoxied to the rear surface of each scintillating sheet transferred light generated in the each of the detectors to a corresponding photomultiplier. According to Tosswill, the ROLEC may be operated moving its axis along another curved or other configuration or without rotation, with symmetry preferred but not essential.
Devices using a segmented germanium crystal have been described by Urie, et al., Rotating Laminar Emission Camera with GE-detector, Med. Phys. 8(6): 865-870 (1981); Mauderli, et al., Rotating Laminar Emission Camera with GE-Detector: An Analysis, Med. Phys. 8(6): 871-876 (1981); Malm, et al., A Germanium Laminar Emission Camera, IEEE Transactions on Nuclear Science, Vol. NS-29, No. 1: 465-468 (1982); and Mauderli, et al., Rotating Laminar Emission Camera with GE-detector: Further Developments, Med. Phys. 14(6): 1027-1031 (1987).
In a first version, a 11.5 mm thick, 45 mm×45 mm segmented germanium detector was placed behind parallel tungsten plates. The crystal was segmented to form a plurality of channels, with the plates aligned with the segmentations. A 4.5 cm diameter viewing aperture was located between the detector and the activity source. Projection data acquired at multiple angular orientations as the detector-collimator assembly was rotated about its center was mathematically reconstructed to form a two-dimensional image of the activity distribution.
A second version simulated a 195 mm×195 mm detection area. Five germanium blocks having a total length of 250 mm segmented into distinct electrical channels. The detector was translated linearly in a direction perpendicular to the plane of the plates to simulate a full-size detector.
One advantage of ROLECs is their high efficiency relative to traditional Anger cameras. In particular, the structure of the collimator permits a greater percentage of incident radiation to reach the surface of the detector. Spatial resolution may be improved by increasing the height of the collimator or reducing the distance between the collimator elements with less effect on efficiency as compared to traditional cameras.
While ROLECs have the advantage of relatively higher efficiency and spatial resolution, they have been expensive to produce inasmuch as significant quantities of relatively expensive detector material have been required. Although detector material cost can be reduced by using a number of relatively smaller detector segments, such an approach complicates the manufacturing process and requires that variations in the response of the individual segments be considered.
Still another drawback is that the collimator slat length has been equal to the detector field of view. This has required additional detector, collimator, and structural material, has introduced spurious counts which do not contribute to useful image information, and has introduced additional mass and bulk into a rotating structure.
Yet another disadvantage to ROLECs has been their circular field of view.
SUMMARY
Embodiments of the present invention address these matters, and others.
According to a first aspect of the present invention, a radiation detection apparatus includes a detector. The detector includes a plurality of longitudinally-spaced radiation attenuative septa which define a plurality of slits. Each slit has a longitudinal and a transverse dimension, the transverse dimension being greater than the longitudinal dimension. The detector also includes a plurality of detector segments, each detector segment having a transverse dimension and detecting radiation received in a corresponding slit. The apparatus also includes a drive operatively connected to one of the detector and the object so as to vary the angular relationship between the slits and the object. The transverse dimensions of the detector segments are less than the longitudinal field of view of the detector.
According to a more limited aspect of the invention, a detector segment includes two or more sub-segments. The sum of the transverse dimensions of the sub-segments is less than the longitudinal field of view.
According to another more limited aspect of the invention, the detector includes first and second radiation attenuative side shields.
According to another more limited aspect of the invention, the aperture aspect ratio of the detector is greater than one.
According to a still more limited aspect, the transverse dimension of the septa are given by the equation
W
y
=
LFOV
×
(
C
z
+
W
z
)
+
H
×
C
y
C
z
+
W
z
+
H
.
According to another more limited aspect of the invention, the transverse dimension of each detector segment is less than the transverse dimension of the corresponding slit.
According to a still more limited aspect, each detector segment includes at least two detector sub-segments. The sum of the transverse dimensions of the sub-segments is less than the transverse dimension of the slit.
According to another limited aspect of the invention, radiation attenuative members are disposed between detector segments which detect radiation received in adjacent slits. The thickness of the radiation attenuative material portion may b

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