Diagnostic tomographic laser imaging apparatus

Abstract

A laser imaging apparatus comprises a platform for supporting a female patient in frontdown, prone position, including an opening permitting a breast of the patient to be vertically pendant below the surface of the platform; scanning mechanism disposed below the platform to scan the breast without breast compression. The scanning mechanism includes a source of coherent near infrared light pulses operably directed to the breast; photodetectors operably disposed to detect the light pulses after passing through the breast; circuit for deriving voltages proportional to the intensity of the received pulses; and computer programmed for storing and displaying images of tissue in the breast derived from the voltages.

I claim:  
     
         1 . A laser imaging apparatus, comprising: 
 a) platform for supporting a female patient in front-down, prone position and having an opening permitting a breast of the patient to be vertically pendant below the surface of the platform;    b) scanning mechanism including a multi-faceted mirror adjacent the underside of said platform, said mirror being-rotated about its own axis and orbited around the pendent breast;    c) a source of coherent near infrared narrow light pulses operably directed to said multi-faceted mirror;    d) optical reflectors directing said light pulses onto the facets of said mirror from a point spaced from said platform for reflection in a series of horizontal fan shaped beams through a breast pendent below said platform;    e) photodetectors operably disposed to detect the light pulses after passing through the breast;    f) circuit for deriving voltages proportional to the intensity of the received pulses; and,    g) computer programmed for storing and displaying images of tissue in the breast derived from the voltages.    
     
     
         2 . An apparatus as in  claim 1 , and further comprising: 
 a) a platform carrying said orbiting mirror and said photodetectors, said platform being adapted for stepping said orbiting mirror and photodetectors vertically downwardly in small increments following each orbit.    
     
     
         3 . An apparatus as defined by  claim 1 , in which said light pulses are of the order of 100 femtoseconds in width and a wavelength of the order of 850 nanoseconds.  
     
     
         4 . An apparatus as defined by  claim 1 , in which said source of light pulses includes a titanium sapphire laser and means including an argon ion laser to pump said titanium sapphire laser.  
     
     
         5 . An apparatus as defined by  claim 1 , in which said detecting means includes a stationary ring of reverse biased avalanche diodes surrounding the orbital path of said mirror.  
     
     
         6 . A method of providing imaging of humanoid breast tissue including: 
 a) supporting a patient in face-down, prone position on a horizontal surface with a breast vertically pendent through an opening in said surface;    b) directing a succession of narrow coherent near infrared light pulses through said breast in a horizontal pattern from a plurality of positions completely surrounding said breast;    c) repeating said last step in a plurality of closely vertically spaced horizontal planes until the entire breast has been scanned;    d) detecting said pulses after passage through said breast tissue and;    e) deriving images of the tissue of said breast from said detected pulses by computed tomography reconstruction.    
     
     
         7 . A scanning chamber for use in scanning human tissue, comprising: 
 a) a frame;    b) photodetectors disposed in a ring on said frame;    c) a rotatable plate supported on said frame, said plate including an opening for permitting the human tissue to be suspended in said opening;    d) said plate having an axis of rotation substantially coincident with center of said ring;    e) a rotatable multi-faceted mirror disposed on said plate such that said mirror makes a complete orbit around said opening when said plate is rotated; and    f) said mirror being positioned such that a laser pulse reflected therefrom is directed across said opening and through the tissue and impinge on said photodetectors during a complete orbit of said mirror.    
     
     
         8 . A scanning chamber, as in  claim 7 , wherein: 
 a) said frame is movable vertically.    
     
     
         9 . A scanning chamber as in  claim 7 , wherein: 
 a) drive screws are operably associated with said frame such that rotations of said screws are effective to lower or raise said plate.    
     
     
         10 . A scanning chamber as in  claim 7 , wherein: 
 a) said frame includes a bottom shelf with a central opening; and    b) wedge prism disposed over said central opening adapted to direct a laser pulse passing through said wedge prism to said mirror.    
     
     
         11 . A scanning chamber as in  claim 7 , wherein: 
 a) bearing assembly adapted to rotatably support said plate from said frame.    
     
     
         12 . A scanning chamber as in  claim 11 , wherein: 
 a) said bearing assembly includes an outer race secured to an opening on said frame; and    b) an inner race secured to said plate.    
     
     
         13 . A scanning chamber as in  claim 7 , wherein: 
 a) said plate includes a ring gear; and    b) drive motor operably connected to said ring gear for rotating said plate.    
     
     
         14 . A scanning chamber as in  claim 7 , wherein: 
 a) said frame includes a bottom shelf with a central opening; and    b) turning mirrors disposed on said shelf adapted to direct a vertical laser beam passing through said central opening to said rotating mirror.    
     
     
         15 . A laser imaging apparatus, comprising: 
 a) a scanning chamber including a source of laser beam for passing through a tissue and at least one photodetector adapted to respond to the laser beam exiting the tissue;    b) an operational amplifier circuit connected to said at least photodetector for converting the current output of said at least detector to voltage; and    c) a clamp circuit for protecting said operational amplifier from overvoltage.    
     
     
         16 . A laser imaging apparatus, as in  claim 15  wherein: 
 a) a time-gate switch circuit for sampling only a portion of the amplitude of the response curve of said at least one detector.  
 
     
     
         17 . A laser imaging apparatus as in  claim 15 , wherein: 
 a) said at least one detector is reverse biased avalanche photodiode.    
     
     
         18 . A laser imaging apparatus as in  claim 15 , wherein: 
 a) said laser source comprises femtosecond pulse width, near infrared laser pulses.    
     
     
         19 . A laser imaging apparatus, comprising: 
 a) a scanning chamber including a source of femtosecond pulse width near infrared laser beam for passing through a tissue and a plurality of photodetectors arranged around the tissue and adapted to respond to the laser beam exiting the tissue;    b) a moving mirror for directing said source of laser beam to each of said photodetectors;    c) an analog to digital converter operably connected to said photodetectors for converting output of said photodetectors to digital form; and    d) a computer programmed to generate an image of the scanned tissue from the output of said converter.    
     
     
         20 . A laser imaging apparatus as in  claim 19 , wherein: 
 a) said photodetectors are reverse biased avalanche photodiodes.    
     
     
         21 . A method for scanning a tissue, comprising the steps of: 
 a) providing a series of laser pulses through the tissue;    b) providing a photodetector disposed to receive the laser pulses after traversing the tissue;    c) determining the free flight arrival time of the laser pulses at the detector when the tissue is not present;    d) determining the delayed arrival time of the laser pulses when the tissue is present in the path of the laser pulses;    e) determining the added time-of-flight of the laser pulses due to the presence of the tissue in the path;    f) adding an increment of time to the added time-of-flight; and    g) sampling the response of the photodetector after a delay of the added time-of-flight and the increment of time, from the free flight arrival time.    
     
     
         22 . A method as in  claim 21 , wherein: 
 a) selecting the increment of time from the range 0-40 picoseconds.    
     
     
         23 . A scanning chamber for use in scanning human tissue, comprising: 
 a) a frame;    b) a rotatable plate supported on said frame, said plate including an opening for permitting the human tissue to be suspended in said opening;    c) photodetectors disposed in on said plate;    d) said plate having an axis of rotation substantially coincident with center of said ring;    e) an oscillating mirror disposed on said plate such that said mirror makes a complete orbit around said opening when said plate is rotated; and    f) said mirror being positioned such that a laser pulse reflected therefrom is directed across said opening and through the tissue and impinge on said photodetectors during a complete orbit of said mirror.