X-ray detector for CT scanners

• US 4,947,412 A
• Filed: 11/23/1988
• Issued: 08/07/1990
• Est. Priority Date: 10/20/1988
• Status: Expired due to Fees

• Current Assignee: Picker International, Inc. (Koninklijke Philips N.V.)
• Original Assignee: Picker International, Inc. (Koninklijke Philips N.V.)
• Inventors: Mattson, Rodney A.
• Primary Examiner(s): Church, Craig E.
• Assistant Examiner(s): Freeman, John C.
• Application Number:
  US07/275,782
• Time in Patent Office: 622 Days
• Field of Search: 378/4, 378/19, 250/370.08, 250/370.09, 250/370.11, 250/368
• US Class Current: 378/19
• CPC Class Codes: A61B 6/032 Transmission computed tomography [CT]
• CPC Class Codes: A61B 6/4021 involving movement of the focal spot
• CPC Class Codes: A61B 6/5205 involving processing of raw data to produce diagnostic data
• CPC Class Codes: G01T 1/20187 Position of the scintillator with respect to the photodiode, e.g. photodiode surrounding the crystal, the crystal surrounding the photodiode, shape or size of the scintillator
• CPC Class Codes: G01T 1/2985 In depth localisation, e.g. using positron emitters; Tomographic imaging (longitudinal and transverse section imaging; apparatus for radiation diagnosis sequentially in different planes, steroscopic radiation diagnosis); using external radiation sources A61B6/02

Abstract

Detectors (20) of a CT scanner (10) have a radiation receiving face (34) which is larger than a photosensitive face (30) of a photodiode (22). Lead wires (28) connect the ends of the diode photosensitive surface to terminals (26). A scintillation crystal (32) has an overhanging portion (38) which overhangs at least the interconnection between the lead wires and the photosensitive face to protect the adjoining areas of the photosensitive face from incident radiation. This enables the radiation receiving surface to be larger than the photosensitive surface. The crystal is either undercut to define the overhanging area or a section of light pipe (60) is provided between the photosensitive surface and the crystal. Increasing the radiation receiving face decreases rotor ripple artifacts. Decreasing the photosensitive face area decreases diode capacitance and increases resistance which improves amplifier performance.

Claims

1. A medical diagnostic scanner comprising:

a source of ionizing radiation for projecting ionizing radiation across an examination region;

a plurality of ionizing radiation detectors disposed across the examination region from the radiation source, each ionizing radiation detector including;

a scintillation crystal having an overhanging cross portion, having a first length and a lower portion having a second length wherein the first length is longer than the second length, the scintillation crystal defining an ionizing radiation receiving face along a length of the cross portion and a second face disposed generally parallel to the ionizing radiation receiving face across the lower portion;

a photodiode having a photosensitive face that has at least one lead wire connected adjacent one end of the photosensitive face, the photosensitive face being coupled in an optically transmissive relationship with the second face of the scintillation crystal such that the scintillation crystal cross portion is displaced from and overhangs a portion of the diode photosensitive face adjacent the lead wire.

2. The scanner as set forth in claim 1 further including a light reflective material coating at least an undersurface of the overhanging cross portion.

3. A medical diagnostic scanner comprising:

a source of ionizing radiation for projecting ionizing radiation across an examination region;

a plurality of ionizing radiation detectors disposed across the examination region from the radiation source, each ionizing radiation detector including;

a scintillation crystal defining an ionizing radiation receiving face of a first length along a length of an overhanging cross portion and a second face disposed generally parallel to the ionizing radiation receiving face;

an optic light pipe section extending between the scintillation crystal second face and a diode photosensitive face;

a photodiode having at least one lead wire connected adjacent one end of the diode photosensitive face, the photosensitive face being coupled in an optically transmissive relationship with the optic light pipe section, the light pipe section having a second length shorter than the first length adjacent the diode photosensitive face, such that the scintillation crystal cross portion is displaced from and overhangs a portion of the diode photosensitive face adjacent the lead wire.

4. An ionizing radiation detector for CT scanners, the detector comprising:

a supporting substrate;

a photodiode mounted on the substrate with a photosensitive face oriented away from the substrate, the photosensitive face having a first length and lead wires connected adjacent one end of the photosensitive face;

an optically transmissive portion having a coupling face of a second length, which second length is shorter than the first length, the optically transmissive portion being spaced from the lead wires and coupled with the photodiode photosensitive face in a light transmissive relationship;

a scintillation crystal optically coupled with the optically transmissive portion and having an ionizing radiation receiving face of a third length, which third length is longer than the first and second lengths, the scintillation crystal being disposed with the ionizing radiation receiving face generally parallel to the photodiode photosensitive face and with a portion of the scintillation crystal spaced from and overhanging the lead wires such that the overhanging portion of the scintillation crystal shields the portion of the diode light sensitive face immediately adjacent the lead wires from ionizing radiation and defines a space therebetween;

a light reflective coating on at least a scintillation crystal overhanging surface defined between the overhanging scintillation crystal portion and a portion of the light sensitive surface immediately adjacent the lead wires.

5. The detector as set forth in claim 4 wherein the scintillation crystal, optically transmissive portion, and the photodiode all have widths that are shorter than the first, second, and third lengths.

6. The detector as set forth in claim 4 wherein the optically transmissive portion is a section of optic light pipe.

7. The detector as set forth in claim 4 wherein the optically transmissive portion includes a scintillation crystal portion.

8. The detector as set forth in claim 4 wherein the optically transmissive portion is generally trapezoidal in cross section.

9. An x-ray detector comprising:

a photodiode having a photosensitive face with a first area;

lead wires connected to and extending from one end of the photosensitive face;

a scintillation crystal for transforming received x-rays into light, the scintillation crystal having;

a central portion which is coupled in an optically transmissive relationship to a major portion of the diode photosensitive face and optically isolated from a portion of the photosensitive face immediately contiguous to the lead wires,

an overhanging portion which is spaced from and overhangs a portion of the diode photosensitive face connected with the lead wires to define an air gap therebetween,

a radiation receiving surface disposed generally parallel to the diode photosensitive face and having a second surface area which is larger than the diode photosensitive face first surface area.

10. An ionizing radiation detector comprising:

a scintillation crystal having a rectangular ionizing radiation receiving face of length l1 and width w, the length being longer than the width;

an optically transmissive portion having a trapezoidal cross section in a plane parallel to length l1 and transverse to the ionizing radiation receiving face, the optically transmissive portion having length of substantially l1 optically coupled with the scintillation crystal and a light output face with a length l2;

a photodiode having a light sensitive face of length l3, where length l3 is longer than length l2 by a sufficient length to accommodate lead wires and shorter than l1, the scintillation crystal, optically transmissive portion, and photodiode being interconnected such that the optically transmissive portion output face is coupled in an optically transmissive relationship to the diode photosensitive face displaced from the lead wires and such that the scintillation crystal overhangs the lead wires and shields a portion of the photosensitive face adjacent the lead wires from ionizing radiation.