Patent Number: 
Section: claims

1. Method for determining a reconstructed image using a particle-optical apparatus, the particle-optical apparatus comprising:a particle source for producing a beam of particles,an object plane on which an object to be imaged may be placed,a condenser system for illuminating the object plane with the beam of particles,a projection system for forming an image of the object plane by imaging particles transmitted through the object on an image plane, anda detector for detecting the image, the detector comprising a semiconductor sensor having an array of pixels for providing a plurality of pixel signals from respective pixels of the array in response to particles incident on the detector, the method comprising:receiving the plurality of pixel signals, anddetermining a reconstructed image using Viterbi Detection on the plurality of pixel signals, by:modelling possible states of a path corresponding to a plurality of possible configurations incident on the detector by determining a plurality of possible state transitions between the pixels, wherein the states are characterized by a run-length constraint that there should be at least two ‘0’s between two ‘1’s;determining the path of state transitions having the highest probability of producing the plurality of pixel signals, anddetermining from the path of state transitions having the highest probability of producing the plurality of pixel signals, the configuration of particles incident on the detector; andmodifying an output of the Viterbi detection by adjusting the determined configuration of particles incident on the detector to define:the modified output to be zero particles for pixels having zero particles in the output of the Viterbi detection, andthe modified output to be one particle for pixels having one or more particles in the output of the Viterbi detection. 2. Method according to claim 1, wherein the states are modelled using a different multiplicity of particles. 3. Method according to claim 1, wherein the states are modelled using different deposited energies of the particle(s). 4. Method according to claim 1, wherein the states are modelled using different point spread functions in modelling deposited energies of the particle(s). 5. Method according to claim 1, wherein the states are used in different iterations of the Viterbi Detection. 6. Method according to claim 1, wherein the array of pixels is a one-dimensional array. 7. Method according to claim 1, wherein the array of pixels is a two-dimensional array and the Viterbi Detection is applied to sequences of pixel signals per row of pixels of the two-dimensional array. 8. Method according to claim 1, wherein the array of pixels is a two-dimensional array and the Viterbi Detection is applied to sequences of pixel signals per column of pixels of the two-dimensional array. 9. Method according to claim 7, wherein the states of the Viterbi Detection correspond to predetermined two-dimensional configurations of particles incident on the detector. 10. Method according to claim 1, further comprising, after having detected one or more incident particles on a pixel, removing a contribution from the detected one or more incident particles from the plurality of pixel signals. 11. Method according to claim 1, wherein the image detected by the detector comprises a dose in a range of 0.0001-0.5 particles per pixel. 12. Method according to claim 1, the method further comprising:receiving a second plurality of pixel signals from the respective pixels of the array in response to particles incident on the detector upon detecting a second image of the object,determining a second reconstructed image using Viterbi Detection on the second plurality of pixel signals by:modelling possible states of a path corresponding to a plurality of possible configurations of particles incident on the detector in detecting the second image by determining a plurality of possible state transitions between the pixels, wherein the states are characterized by a run-length constraint that there should be at least two ‘0’s between two ‘1’s;determining the path of state transitions having the highest probability of producing the second plurality of pixel signals, anddetermining from the path of state transitions having the highest probability of producing the second plurality of pixel signals, a second configuration of particles incident on the detector; andmodifying the output of the Viterbi detection on the second plurality of pixel signals by adjusting the second determined configuration of particles incident on the detector to define:the modified output to be zero particles for pixels having zero particles in the output of the Viterbi Detection, andthe modified output to be one particle for pixels having one or more particles in the output of the Viterbi detection, andcombining the modified output of the Viterbi Detection for the first reconstructed image and the modified output of the Viterbi Detection for the second reconstructed image to form a combined reconstructed image. 13. Method according to claim 1, further comprising:producing a beam of particles,placing an object to be imaged on an object plane,illuminating the object plane with the beam of particles,forming an image of the object plane by imaging particles transmitted through the object on an image plane, anddetecting the image with the detector comprising the semiconductor sensor and providing a plurality of pixel signals from the respective pixels of the array in response to the particles incident on the detector. 14. Particle-optical apparatus comprising:a particle source for producing a beam of particles,an object plane on which an object to be imaged may be placed,a condenser system for illuminating the object plane with the beam of particles,a projection system for forming an image of the object plane by imaging particles transmitted through the object on an image plane,a detector for detecting the image, the detector comprising a semiconductor sensor having an array of pixels for providing a plurality of pixel signals from respective pixels of the array in response to particles incident on the detector, anda signal processor configured to perform the method of claim 1. 15. A computer program hardware product carrying instructions for causing a processor system to perform the method according to claim 1. 16. A method according to claim 8, wherein the states of the Viterbi Detection correspond to predetermined two-dimensional configurations of particles incident on the detector. 17. A method for determining a reconstructed image using a particle-optical apparatus, comprising:providing a particle optical apparatus having a detector for detecting an image, the detector providing a plurality of pixel signals from respective pixels in response to particles incident on the detector;receiving the plurality of pixel signals;determining a reconstructed image using Viterbi detection on the plurality of pixel signals, by:modelling possible states of a path corresponding to a plurality of possible configurations incident on the detector by determining a plurality of possible state transitions between the pixels, wherein the states are characterized by a run-length constraint that there should be at least two ‘0’s between two ‘1’s;determining the path of state transitions having the highest probability of producing the plurality of pixel signals, the most likely configuration of particles incident on the detector; andmodifying a Viterbi output by adjusting the determined configuration of particles incident on the detector to define:the modified output to be zero particles for pixels having zero particles in the output of the Viterbi detection, andthe modified output to be one particle for pixels having one or more particles in the output of the Viterbi detection. 18. The method of claim 17, wherein the different states are modelled using a different multiplicity of particles. 19. The method of claim 17, wherein the different states are modelled using different deposited energies of the particle(s). 20. The method of claim 17, wherein the different states are modelled using different point spread functions in modelling deposited energies of the particle(s).