1

L. Yaroslavsky. Fundamentals of Digital Image Processing. Course 0555.3230

Lecture 1. IMAGING AND IMAGING DEVICES

- Vision in Live Creatures- First artificial imaging systems and techniques

- Magnifying glass and spectacles- Painting art- Camera-obscura (pinhole camera)

- Optical microscope and telescope- Photography- X-ray imaging- Radiography- Electron microscopy- Electronic television- Acoustic imaging- Scanned proximity probe microscopes- Linear tomography and laminography- Interferometry; fringe methods of active vision- Crystallography- Coded Aperture (multiplexing techniques)- Synthetic aperture radars- Computed tomography- Magnetic resonance imaging- Holography- Digital holography and image processing

Home work:- List and briefly describe image processing biomedical applications you know- Find and briefly describe imaging devices other then those that were described in

the lecture

References1. "History of the Light Microscope" (http://www.utmem.edu/personal/thjones/hist/hist_mic.htm)2. E. Ruska, The Development of the Electron Microscope and of Electron Microscopy, Nobel Lecture,Dec. 8, 1986.3. G. Binning, H. Rohrer, Physica ,127B, 37, 19844. R. Wiesendanger and H.-J. Güntherodt, Introduction, Scanning Tunneling Microscopy I, GeneralPrinciples and Applications to Clean and Absorbate-Covered Surfaces, Springer Verlag, Berlin, 19945. http://stm2.nrl.navy.mil/how-afm/how-afm.html)6. R. Bracewell, Two-dimensional Imaging, Prentice Hall, 19957. L.P. Yaroslavsky , The Theory of Optimal Methods for Localization of Objects in Pictures, In:Progress in Optics, Ed. E. Wolf, v.XXXII, Elsevier Science Publishers, Amsterdam, 19938. D. Gabor, A New Microscopic Principle, Nature, v. 161, 777-778, 1948, Nobel Prize9. E.N. Leith, J. Upatnieks, New techniques in Wavefront Reconstruction, JOSA, v. 51, 1469-1473,196110. Yu . N. Denisyuk, Photographic reconstruction of the Optical Properties of an Object in its OwnScattered Radiation Field, Dokl. Akad. Nauk SSSR, v. 1444, 1275-1279, 1962).11. L. Yaroslavsky, N. Merzlyakov, Methods of Digital Holography, Plenum Press, N.Y., 198012. L. Yaroslavsky, M. Eden, Fundamentals of Digital Optics, Birkhauser, Boston, 199513. L. Yaroslavsky, From Photo-graphy to *-graphies, Lecture notes,http://www.eng.tau.ac.il/~yaro/lectnotes/index.html14. L. Yaroslavsky, Digital Holography and Image Processing, Kluwer, Boston, 2003

2

Vision in Live CreaturesFirst imaging systems were invented by the Nature.

(From: Richard Dawkins, Climbing Mount Unprobable, W. W. Nortom Co, New York, 1998 )

Fly eye

Cup eyes from around the animalkingdom. (a) - flatworm; (b) –bevalve mollusc; (c) – polychaetworm; (d) - limpet

A range ofinvertebrate eyes:(a) – nautilus pinholeeye; (b) - marinesnail; (c) – bivalvemollusc;(d) – abalone;(e) - ragworm

3

Optics and nerve system of human eye

(From: J. S. Lim, Ywo-dimensional Signal and Image Processing, Prentice Hall, Englewood Cliffs, N.J., 1990)

Eye retina: rods and cones(adopted from H. Hofer, D. R. Williams, The Eye’s Mechanisms for Autocalibration, Optics andPhotonic News, January, 2002, p. 34-39 and R. C. Gonzalez< R. E. Woods, Digital Image Processing,Prentice Hall, 2002)

Density of cones in the area of the highest acuity (fovea) ~100.000 elements/mm2.The number of cones in this area is about 300000. Resolving power of human visionis about 1’.

Natural imaging systems (vast majority)- are discrete- are shift invariant- involve image processing (object tracking, stereo image processing, color constancy,etc.)

Light

4

Ever first artificial imaging devices:Magnifying glass and spectacles (Graeco-Roman times). Pliny the Elder wrote in 23-79 A.D.:

"Emeralds are usually concave so that they may concentrate the visual rays.The Emperor Nero used to watch in an Emerald the gladatorial combats."

Spectacles were invented (re-invented) around 1280-1285 in Florence, Italy. It'suncertain who the inventor was, Some give credit to a nobleman named Amati(Salvino degli Armati, 1299 ). It has been said that he made the invention, but toldonly a few of his closest friends. (adopted from [1])

Painting art

- A woodcut by Albrecht Dürer showing the relationship between a scene, a center ofprojection and the picture planeCamera-obscura (pinhole camera) (Ibn Al Haytam, X century):

Images were regarded as point by point projections of objects on an image plane

Object

Image

Image plane

5

Invention of optical microscope.Inventor of optical microscope is not known. Credit for the first microscope is

usually given to Dutch (from other sources, Middleburg, Holland) spectacle-makerJoannes and his son Zacharios Jansen. While experimenting with several lenses ina tube, they discovered (around the year 1595) that nearby objects appeared greatlyenlarged. (partly adopted from [1]) . That was the forerunner of the compoundmicroscope and of the telescope. The father of microscopy, AnthonyLeeuwenhoek of Holland (1632-1723), startedas an apprentice in a dry goods store wheremagnifying glasses were used to count thethreads in cloth. He taught himself new methodsfor grinding and polishing tiny lenses of greatcurvature which gave magnifications up to 270,the finest known at that time. These led to thebuilding of his microscopes and the biologicaldiscoveries for which he is famous. He was thefirst to see and describe bacteria, yeast plants,the teeming life in a drop of water, and thecirculation of blood corpuscles in capillaries.

Robert Hooke, the English father ofmicroscopy, re-confirmed Anthony vanLeeuwenhoek's discoveries of the existence oftiny living organisms in a drop of water. Hookemade a copy of Leeunwenhoek's microscope andthen improved upon his design

Microscope of Hooke (R. Hooke,Micrographia, 1665)

Modern Zeiss microscope

Newton’s telescope-refractor

Hubble spacetelescope

Telescope (Zacharias Joannides Jansen of Middleburg,1590)In 1609, Galileo, father of modern physics and astronomy,heard of these early experiments, worked out the principlesof lenses, and made a much better instrument with afocusing device.Huygens (“Dioptrica, de telescopiis”) held the view thatonly a superhuman genius could have invented the telescopeon the basis of theoretical considerations, but the frequentuse of spectacles and lenses of various shapes over a periodof 300 years contributed to its chance invention.The scientific impetus produced by the great discoveriesmade with the telescope can be gauged from the enthusiasticmanner in which Huygens in the “Dioptrica” speaks of thesediscoveries. He describes how Galileo was able to see themountains and valleys of the moon, to observe sun-spotsand determine the rotation of the sun, to discover Jupiter’ssatellites and the phases of Venus, to resolve the Milky Wayinto stars, and to establish the differences in apparentdiameter of the planets and fixed stars (after E. Mach, Theprinciples of Physical Optics, Dover Publ., 1926).

6

Photographic camera: a revolutionary step

In the 19-th century, scientists began to explore ways of “fixing” the imagethrown by a glass lens. (H. Nieps, 1826; J. Dagherr, 1836; W. F. Talbot, 1844)

The first method of light writing was developed by the French commercialartist Louis Jacque Mande Daguerre (1787-1851). The daguerrotype was made on ashhet of silver-plated coper, which could be inked and then printed to produceaccurate reproduction of original works or scenes. The surface of the copper waspolished to a mirrorlike brilliance, then rendered light sensitive by treament withiodine fumes. The copper plate was then exposed to an image sharply focused by thecamera’s well-ground, optically correct lens. The plate was removed from the cameraand treated with mercury vapors to develop the latent image. Finally, the image wasfixed by removal of the remaining photosensitive salts in a bath of hyposulfite andtoned with gold chloride to improve contrast and durability. Color, made of powderedpigment, was applied derectly to the metal surface with a finely pointed brush.

Daguerre’s attempt to sell his process (the daguerreotype) through licensingwas not successful, but he found an enthusiastic supporter in Francois Arago, aneminent member of the Academie des Sciences in France. Arago recommended thatthe French government compensate Daguerre for his considerable efforts, so that thedaguerreotype process could be placed at the service of the entire world. The Frenchgovernment complied, and the process was widely publicized by F. Arago, 19.8.1839at a meeting of L’Institut, Paris on August 19, 1839, as a gift to the world fromFrance.

Astronomers were among the first to employ the new imaging techniques. In1839-1840: John W. Draper, professor of chemistry at New York University, madefirst photographs the moon in first application of daguerreotypes in astronomy. Thephotoheliograph, a device for taking telescopic photographs of the sun, was unveiledin 1854.

Fundamental innovation:

Imaging optics was supplemented with photo sensitive recording material. Imageformation and image display were separated. Photographic plate/film combines threefunctions: image recording, image storage and image display

Fast progress of photographic techniques

In 1840 optical means used to reduce daguerreotype exposure times to 3-5 min.In1841 William Henry Fox Talbot patents a new process involving creation of papernegatives. By the end of 19-th century, photography had become an important meansfor scientific research and also a commercial item that entered people every day life. Ithas been keeping this status till very recently.

7

X-ray imagingNext mile stones in the evolution of imaging techniques are X-ray imaging andradiography.X-rays were discovered by Wilhelm Conrad Röntgen, Nov. 8,1895; Institute ofPhysics, University of Würzburg, when he experimented with cathode rays. (1-stNobel Prize, 1901)

Wilhelm Conrad Röntgen (1845 - 1923) One of the first medical X-ray images (ahand with small shots in it)

Fluorography 1907 Fluorography 2000

8

Photography had played a decisive role inthe discovery of radioactivity as well.

In 1896, Antoine Henri Becquerelaccidentally discovered radioactivitywhile investigating phosphorescence inuranium salts.

This discovery eventually led, along withother, to new imaging techniques,radiography

Modern gamma-camera:Gamma-ray collimator + Gamma-ray-to light converter + photo sensitive array + CRTas a displayCollimator separates rays from different object points; this goal is achieved by theexpense of energy losses.

9

Next mile stone: Electronic imaging.Electron microscopy (1931. Ernst Ruska, The Nobel Prize, 1986)Electron optics + luminescent screen or electron sensitive array + CRT display

Transmission Electron Microscope:Atoms of gold (Au_clusters) on MoS2.

Scanning electron microscope image ( fromhttp://www.sst.ic.ac.uk/intro/AFM.htm )

10

Electronic televisionA bit of history~1910, Boris Lvovich Rosing, St. Petersburg, Russia, suggested CRT as a display device~1920-25, Rosing’s student, Vadimir Kozmich Zvorykin (1889-1982) – iconoscope& kinescope,Jan. 1929 V. Zvorykin met David Sarnov from RCA and got financial grant from him~1935 : first regular TV broadcasting, Britain and USA

An important step: image discretization.Originally it was dictated by the need to transmit 2-D images over 1-Dcommunication channels

Modern CCD and CMOS cameras

Radar (~1935), Sonar:beam forming antenna + space scanning mechanism + CRT as a display

11

Acoustic microscope (1950-th, after R. Bracewell, Two-dimensional Imaging, Prentice Hall,

1995):

A monochromatic sound pulse can be focused to a point on the solid surface of anobject by a lens (sapphire rode), and the reflection will return to the lens to begathered by a receiver. The strength of the reflection depends on the acousticalimpedance looking into the solid surface relative to the impedance of the propagatingmedia. If the focal point performs a raster scan over the object, a picture of the surfaceimpedance is formed. Acoustic impedance of a medium depends on its density andelastic rigidity. Acoustic energy that is not reflected at the surface but enters the solidmay be only lightly attenuated and then reflect from surface discontinuities to revealan image of the invisible interior. With such a device, an optical resolution can beachieved. A major application is in the semiconductor industry for inspectingintegrated circuits.

The idea of focusing an acoustic beam was originally suggested by Rayleigh. Theapplication of scanning acoustic microscopes goes back to 1950.

A scanning optical microscope can also be made on the same principle. It has value asa means of imaging an extended field without aberrations associated with a lens.

ElectricOscillator

Receiver

Sapphir(Al2O3) rode

Piezo-electrictransducer

(niobium titanate)

Movable specimen(immersed in a liquid)

12

Scanned-proximity probe (SPP) microscopes.SPP- microscopes work by measuring a local property - such as height, optical

absorption, or magnetism - with a probe or "tip" placed very close to the sample. Thesmall probe-sample separation (on the order of the instrument's resolution) makes itpossible to take measurements over a small area. To acquire an image the microscoperaster-scans the probe over the sample while measuring the local property in question.Scanned-probe systems do not use lenses, so the size of the probe rather thandiffraction effects generally limit their resolution

Tunnel microscope (1980-th; The Nobel prize 1986)

Schematic of the physical principle and initial technicalrealization of Scanning Tunnel Microscope. (a) shows apexof the tip (left) and the sample surface (right) at amagnification of about 108. The solid circles indicate atoms,the dotted lines electron density contours. The path of thetunnel current is given by the arrow. (b) Scaled down byfactor of 104. The tip (left) appears to touch the surface(right). (c) STM with rectangular piezo drive X,Y,Z of thetunnel tip at left and “loose” L (electrostatic “motor”) forrough positioning (ìm to cm range) of the sample S (fromG. Binning, H. Rohrer: Physica 127B, 37, 1984)

Scanning tunnel microscope image ofsilicon surface. The image shows two

single layer steps (the jagged interfaces)separating three terraces. Because of thetetrahedral bonding configuration in thesilicon lattice, dimer tow directions are

orthogonal on terraces joined by asingle layer step. The area pictured is

30x30 nm

A conductive sample and a sharp metal tip, which acts as a local probe, are broughtwithin a distance of a few ångstroms, resulting in a significant overlap of theelectronic wave functions (see the figure). With applied bias voltage (typicallybetween 1mV and 4V), a tunelling current (typically between 0.1nA and 10 nA) canflow from the occupied electronic states near the Fermi level of one electrode into theunoccupied states of the other electrode. By using a piezo-electric drive system of thetip and a feedback loop, a map of the surface topography can be obtained. Theexponential dependence of the tunneling current on the tip-to-sample spacing hasproven to be the key for the high spatial resolution which can be achieved with theSTM. Under favorable conditions, a vertical resolution of hundredths of an ångstromand the lateral resolution of about one ångstrom can be reached. Therefore, STM canprovide real-space images of surfaces of conducting materials down to the atomicscale. (from R. Wiesendanger and H.-J. Güntherodt, Introduction, Scanniing Tunneling Microscopy I,General Principles and Applications to Clean and Absorbate-Covered Surfaces, Springer Verlag,Berlin, 1994)

13

Atomic force microscope (after http://stm2.nrl.navy.mil/how-afm/how-afm.html).

The atomic force microscope is one of about two dozen types of.

Figure 1. Concept of AFM and the optical lever: (left) a cantilever touching a sample;(right) the optical lever. Scale drawing; the tube scanner measures 24 mm in diameter,while the cantilever is 100 µm long.

AFM operates by measuring attractive or repulsive forces between a tip andthe sample. In its repulsive "contact" mode, the instrument lightly touches a tip at theend of a leaf spring or "cantilever" to the sample. As a raster-scan drags the tip overthe sample, some sort of detection apparatus measures the vertical deflection of thecantilever, which indicates the local sample height. Thus, in contact mode the AFMmeasures hard-sphere repulsion forces between the tip and sample. In noncontactmode, the AFM derives topographic images from measurements of attractive forces;the tip does not touch the sample.

AFMs can achieve a resolution of 10 pm, and unlike electron microscopes, canimage samples in air and under liquids. To achieve this most AFMs today use theoptical lever. The optical lever (Figure 1) operates by reflecting a laser beam off thecantilever. Angular deflection of the cantilever causes a twofold larger angulardeflection of the laser beam. The reflected laser beam strikes a position-sensitivephotodetector consisting of two side-by-side photodiodes. The difference between thetwo photodiode signals indicates the position of the laser spot on the detector and thusthe angular deflection of the cantilever. Image acquisition times is of about oneminute.

14

2.5 x 2.5 nm simultaneous topographic andfriction image of highly oriented pyrolytic graphic(HOPG). Each bump represents one carbon atom.As the tip moves from right to left, it bumps intoan atom and gets stuck behind it. The scannercontinues to move and lateral force builds up untilthe tip slips past the atom and sticks behind thenext one.

“Steps”

Atomic force microscope, University of Konstanz, May 1991

The ability of AFM to image at atomic resolution, combined with its ability to imagea wide variety of samples under a wide variety of conditions, has created a great dealof interest in applying it to the study of biological structures. Images have appeared inthe literature showing DNA, single proteins, structures such as gap junctions, andliving cells.

15

Linear tomography (~1930-th)

Schematic diagram of linear tomography. Due to the synchronous movement of theX-ray source and X-ray sensor, certain plane cross-section of the object is alwaysprojected in the same place of the sensor while others are projected with adisplacement and therefore will appear blurred in the resulting image.

Application in dentistry

Moving stage with a X-ray sensor

O1 O2 O3

Moving X-ray point source

Focal plane

Image 3 Image 2 Image 1

16

Laminography

The principle of laminography (http://lca.kaist.ac.kr/Research/2000/X_lamino.html)

X-ray point source moving in the source plane over a circular trajectory projectsobject onto X-ray detector plane. The detector moves synchronously to the source insuch a way as to secure that a specific object layer is projected on the same place onthe detector array for whatever position of the source. The plane of this selected layeris called “focal plane’. Projections of other object layers located above or beneath ofthe “focal plane” will, for different position of the source, be displaced. Therefore ifone sums up all projections obtained for different positions of the source, projectionsof the focal plane layers will be accumulated coherently producing a sharp image ofthis layer while other layers projected with different displacement in differentprojections will produce a blurred background image. The more projections areavailable the lower will be the contribution of this background into high frequencycomponents of the output image.

Illustration of restoration of different layers of a printed circuit board

17

Optical interferometry and moire (Fringe) techniques

Schematic diagram of shapemeasurement by mean ofstructured light illumination(1 – fringe image; 2 – imagesensor; 3 – illumination source;4- support; 5 - object)

Schematic diagram of optical interferometry

Interferograms without (left) and with (right) spatial carrier

Object’s profile

Semi-transparent

mirror

Semi-transparen

t mirror

Mirror

Mirror

Photosensitivemedium

18

2. TRANSFORM IMAGING TECHNIQUES

The main advantages of the direct image plane imaging- It allows generating images that can be dericely perceived by human vision- It allows direct interpretation of a priori knowledge on images in terms of those of

objectsFundamental drawbacks of direct image plane imaging techniques:- They require access to individual points (locations) of objects- They require high sensitivity of the sensor: signal energy

Probably, the very first example of indirect imaging method was that of X—raycrystallography (Max Von Laue, 1912, Nobel Prize 1914-1918)

In 1912 Max von Laue and two students (Walter Friedrich and Paul Knipping)demonstrated the wave nature of X-rays and periodic structure of crystals byobserving the diffraction of X-rays from crystals of zinc sulfide. Discovery ofdiffraction of X-rays had a decisive value in the development of physics and biologyof XX-th century. One of the most remarkable scientific achievements that is based onX-ray crystallography was discovery by J. Watson and F. Crick of spiral structure ofDNA (Nobel Prize, 1953)

19

“Coded” aperture (multiplexing) techniques (1970-th)

Pinhole camera (camera obscura) has a substantial advantage over lenses - it hasinfinite depth of field, and it doesn't suffer from chromatic aberration. Because itdoesn't rely on refraction, pinhole camera can be used to form images from X-ray andother high energy sources, which are normally difficult or impossible to focus.

The biggest problem with pinholes is that they let very little light through to the filmor other detector. This problem can be overcome to some degree by making the holelarger, which unfortunately leads to a decrease in resolution. The smallest featurewhich can be resolved by a pinhole is approximately the same size as the pinholeitself. The larger the hole, the more blurred the image becomes. Using multiple, smallpinholes might seem to offer a way around this problem, but this gives rise to aconfusing montage of overlapping images. Nonetheless, if the pattern of holes iscarefully chosen, it is possible to reconstruct the original image with a resolutionequal to that of a single hole.

Detector array(( ))y,xb

Coding mask(( ))y,xm

Image planedetector

Source of irradiationPinhole camera

a(x,y)

20

Transform imaging :Synthetic aperture radar (C.Wiley, USA, 1951):

Side looking radar: Direct imaging in “range” co-ordinate and transform imaging in“azimuth” co-ordinate

21

Radar map of Venus

If the thick clouds covering Venus were removed, how would the surface appear?Using an imaging radar technique, the Magellan spacecraft was able to lift the veilfrom the Face of Venus and produce this spectacular high resolution image of theplanet's surface. Red, in this false-color map, represents mountains, while bluerepresents valleys. This 3-kilometer resolution map is a composite of Magellanimages compiled between 1990 and 1994. Gaps were filled in by the Earth-basedArecibo Radio Telescope. The large yellow/red area in the north is Ishtar Terrafeaturing Maxwell Montes, the largest mountain on Venus. The large highland regionsare analogous to continents on Earth. Scientists are particularly interested in exploringthe geology of Venus because of its similarity to Earth.

22

Principles of reconstructive tomographyThe x-ray-based computerized tomography (CT) was introduced by Hounsfield in1973 (Nobel pize, ~1980)

Schematic diagram of parallel beam projection tomography

In computer tomography, a set of object’s projections taken a different observationangles is measured and used for subsequent reconstruction of the object:

ϑϑ ξξ

(( ))y,xObj

(( ))ξξϑϑ,ojPr

X-ray sensitiveline array

Parallel X-raybeam

y

x

23

Schematic diagram of micro-tomography

Surface rendering of a fly head reconstructed using a SkyScan micro-CT scannerModel L1072 (Advanced imaging, July 2001, p. 22)

24

Magnetic resonance (Nuclear magnetic resonance , NMR,MRI) tomography.

Schematic diagram of NMR imaging

MRI is based on the principles of nuclear magnetic resonance (NMR), a spectroscopictechnique used by scientists to obtain microscopic chemical and physical informationabout molecules. An effect observed when an atomic nucleus is exposed to radiowaves in the presence of a magnetic field. A strong magnetic field causes themagnetic moment of the nucleus to precess around the direction of the field, onlycertain orientations being allowed by quantum theory. A transition from oneorientation to another involves the absorption or emission of a photon, the frequencyof which is equal to the precessional frequency. With magnetic field strengthscustomarily used the radiation is in the radio-frequency band. If radio-frequencyradiation is supplied to the sample from one coil and is detected by another coil, whilethe magnetic field strength is slowly changed, radiation is absorbed at certain fieldvalues, which correspond to the frequency difference between orientations. An NMRspectrum consists of a graph of field strength against detector response. This providesinformation about the structure of molecules and the positions of electrons withinthem, as the orbital electrons shield the nucleus and cause them to resonate at differentfield strengths. (The Macmillan Encyclopedia 2001, © Market House Books Ltd 2000)

x

y

zStrong magnetic field RF inductor

and sensor

RF receiver

Magnetand

“gradient”coils

RF impulsegenerator

Reconstructionand display device

Object

25

Magnetic resonance imaging (MRI) is an imaging technique used primarily in medicalsettings to produce high quality images of the inside of the human body. MRI startedout as a tomographic imaging technique, that produced an image of the NMR signal ina thin slice through the human body. MRI has advanced beyond a tomographicimaging technique to a volume imaging technique.The brief history of MRI

Felix Bloch and Edward Purcell, both of whom were awarded the Nobel Prizein 1952, discovered the magnetic resonance phenomenon independently in 1946. Inthe period between 1950 and 1970, NMR was developed and used for chemical andphysical molecular analysis.

In 1971 Raymond Damadian showed that the nuclear magnetic relaxationtimes of tissues and tumors differed, thus motivating scientists to consider magneticresonance for the detection of disease.

In 1973 the x-ray-based computerized tomography (CT) was introduced byHounsfield. This date is important to the MRI timeline because it showed hospitalswere willing to spend large amounts of money for medical imaging hardware.Magnetic resonance imaging was first demonstrated on small test tube samples thatsame year by Paul Lauterbur. He used a back projection technique similar to that usedin CT.

In 1975 Richard Ernst proposed magnetic resonance imaging using phase andfrequency encoding, and the Fourier Transform. This technique is the basis of currentMRI techniques. A few years later, in 1977, Raymond Damadian demonstrated MRIof the whole body. In this same year, Peter Mansfield developed the echo-planarimaging (EPI) technique. This technique will be developed in later years to produceimages at video rates (30 ms / image).

By 1986, the imaging time was reduced to about five seconds, withoutsacrificing too much image quality. The same year people were developing the NMRmicroscope, which allowed approximately 10 µm resolution on approximately one cmsamples. In 1987 echo-planar imaging was used to perform real-time movie imagingof a single cardiac cycle. In this same year Charles Dumoulin was perfecting magneticresonance angiography (MRA), which allowed imaging of flowing blood without theuse of contrast agents.

In 1991, Richard Ernst was rewarded for his achievements in pulsed FourierTransform NMR and MRI with the Nobel Prize in Chemistry. In 1993 functional MRI(fMRI) was developed. This technique allows the mapping of the function of thevarious regions of the human brain. Six years earlier many clinicians thought echo-planar imaging primary applications was to be in real-time cardiac imaging. Thedevelopment of fMRI opened up a new application for EPI in mapping the regions ofthe brain responsible for thought and motor control.

In 2003 Nobel Prize in physiology medicine was awarded to Paul C.Lautenbur and Sir Peter Mansfield, UK for their discoveries concerning magneticresonance imaging.

26

Holography

Invention of holography by D. Gabor was motivated by the desire to improveresolution power of electron microscope that was limited by the fundamentallimitations of the electron optics. The term “holography” originates from Greece word“holos” (çùëùó). By this, inventor of holography intended to emphasize that inholography full information regarding light wave, both amplitude and phase, isrecorded by means of interference of two beams, object and reference one. Due to thefact that at that time sources of coherent electron radiation were not available, Gaborcarried out model optical experiments to demonstrate the feasibility of the method.However, powerful sources of coherent light were also not available at the time, andholography remained an “optical paradox” until the invention of lasers. The very firstimplementation of holography were demonstrated in 1961 by radio-engineers E. Leitha nd J. Upatnieks and by optician Yu. Denisyuk.- D. Gabor, A New Microscopic Principle, Nature, v. 161, 777-778, 1948, Nobel Prize- E.N. Leith, J. Upatnieks, New techniques in Wavefront Reconstruction, JOSA, v. 51, 1469-1473,

1961- Yu. N. Denisyuk, Photographic reconstruction of the Optical Properties of an Object in its Own

Scattered Radiation Field, Dokl. Akad. Nauk SSSR, v. 1444, 1275-1279, 1962).

Basic principle of holography is illustrated in the figure.

Recording hologram:

Object

Source ofcoherent light

Mirror

Recordingmedium

Object beam

Reference beam(( ))refref iA ΦΦππ2exp

Object beam(( ))objobj iA ΦΦππ2exp

27

Reconstructing hologram:

Schematic diagram of hologram reconstruction

Virtualobject(“real”)

Source ofcoherent light

Mirror

Hologram

Object beam

Referencebeam

Virtualobject

(“imaginary”

Scatteredreference beam

28

Reflection (Denisyuk type) hologram

Object

Objectbeam Photographic

plate Mirror

Laserbeam

Schematic diagram of hologram recording

Referencebeam

Hologram

Virtualobject

Point whitelight source

Hologram playback

29

Digital holography: synthesis and analysis of holograms by digital processing

Synthesis:

Scheme of object visual observation

Mathematical model or signal – computation of the hologram –recording synthesizedhologram

Scheme for visual observation of computer generated holoogram

Recording computer generated hologram is a specific digital-to-analog conversionprocess

Illumination

Light scatteredby object Observation

surface

Computergeneratedhologram

Point source ofcoherent light

30

Digital reconstruction of holograms. Holographic microscopy

Optical hologram and its digital reconstruction (L. Yaroslavsky, N. Merzlyakov, Methods of

Digital Holography, Consult. Bureau, New York, 1980)

Digital holographic microscopy

Hologramsensor

Computer:Hologramreconstructionand imageprocessing

Laser

Collimator

Beam spatialfilter

Lens

Microscope

Object table

DigitalPhoto-graphiccamera

Computer

31

Digital processing of optical and similar signals:

New qualities that are brought to imaging systems by digital computers andprocessors:- flexibility and adaptability. The most substantial advantage of digital computers as

compared with analog electronic and optical information processing devices isthat no hardware modifications are necessary to reprogram digital computers tosolving different tasks. With the same hardware, one can build an arbitraryproblem solver by simply selecting or designing an appropriate code for thecomputer. This feature makes digital computers also an ideal vehicle forprocessing optical signals adaptively since, with the help of computers, they canadapt rapidly and easily to varying signals, tasks and end user requirements.

- digital computers integrated into imaging systems enable them to perform not onlyelement-wise and integral signal transformations such as spatial and temporalFourier analysis, signal convolution and correlation that are characteristic foranalog optics but any operations needed. This removes the major limitation ofoptical information processing and makes optical information processingintegrated with digital signal processing almost almighty.

- acquiring and processing quantitative data contained in optical signals, andconnecting optical systems to other informational systems and networks is mostnatural when data are handled in digital form. In the same way as in economicscurrency is a general equivalent, digital signals are general equivalent ininformation handling. A digital signal within the computer that represents anoptical one is, so to say, purified information carried by the optical signal anddeprived of its physical integument. Thanks to its universal nature, the digitalsignal is an ideal means for integrating different informational systems.

Basic problems:- Digital representation of signals- Digital representation of signal transforms- Development of adaptive algorithms to achieve potential quality limits- Efficient computational algorithms