pacs picture archiving and communication system
Download
Skip this Video
Download Presentation
PACS: Picture Archiving and Communication System

Loading in 2 Seconds...

play fullscreen
1 / 125

Chapter 8: PACS: Picture Archiving and Communication System - PowerPoint PPT Presentation


  • 418 Views
  • Uploaded on

PACS: Picture Archiving and Communication System. Feipei Lai National Taiwan University. PACS. A comprehensive computer system that is responsible for the electronic storage and distribution of medical images in the medical enterprise. Reduce costs Improve patient care. PACS 網路架構圖.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Chapter 8: PACS: Picture Archiving and Communication System' - Jimmy


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
pacs picture archiving and communication system

PACS: Picture Archiving and Communication System

Feipei Lai

National Taiwan University

slide2
PACS
  • A comprehensive computer system that is responsible for the electronic storage and distribution of medical images in the medical enterprise.
  • Reduce costs
  • Improve patient care
slide5
PACS 網路架構圖

1. Core Switch 6509 擺放位置

兩台放置於東址資訊室,另外兩台放置於西址影醫部新增之機房

2.Main PACS client 連接方式

Client 端透過 Edge Switch 連接到 Core Switch上,每台 Edge Switch再分別透過光纖連結到不同的 Core Switch上做線路備援

3.舊有 RAD PACS 設備連接方式與線路更新

西址影醫部相關網點均加以重新佈線,東址影醫部所新增之網點亦加以重新佈設,並於東址影醫部新增所需之機櫃放相關之設備。所有 RAD PACS的設備均將連接至新的 PACS Core Switch上,並針對相關的流量設定一個獨立的網段,讓不相干的人無法存取影醫部的 PACS資料。

slide6
4. 影醫高階設備數量與連接方式

東址影醫部高階設備為 30台,西址影醫部為 3台。連接方式為東址影醫新增一台48埠10/100/1000之交換器,西址影醫部新增一台24埠10/100/1000之交換器。然後再將設備利用光纖連接到 Core Switch上

5. 公館分院與總院間 RAD PACS存取方式

為了相關資訊的存取安全性,目前有兩種作法

a.利用設備本身的控制功能,設定ACL之機制,限制相關的存取權限,讓只有影醫部的 IP才可存取 RAD PACS的資料。

b.直接拉專線做連結。

evolution of medical tomographic imaging as seen from a darwinian perspective
Evolution of Medical Tomographic Imaging – As Seen From a Darwinian Perspective
  • Imaging devices --- life-forms
  • Imager variability --- genes
  • Random appearance of new ideas --- mutations
  • Mass manufacture --- reproduction
  • Integration of different ideas --- generic recombination
  • Marketplace Pressures --- natural selection
medical images
Medical images
  • Topographic imaging
    • Represents the surface of the body
  • Projection imaging
    • The interactions of radiation penetrating along a known path of the radiation through the body
  • Tomographic imaging
    • The spatial distribution of the local interaction of the radiation with tissue in a thin slice through the body.
medical images10
Medical images
  • The quality of the images is represented by contrast and resolution.
  • The contrast is determined by the nature of the interaction of the radiation with the tissue material (e.g., via partial absorption) or its structure (e.g., via reflection) or the preferential accumulation of indicator materials (e.g., iodine for X-ray, gadolinium 釓 for Magnetic Resonance Imaging, microbubles in the Ultrasound or radionuclides for Scintigraphy 閃爍造影術 ).
medical images11
Medical images
  • The resolution is expressed as spatial, temporal or contrast.
  • Temporal resolution involves the exposure time required to complete the scan of a single image and the “frame rate” of the sequential individual images.
medical images12
Medical images
  • Plays a major role in medical research activities such as detection and quantitation of pathophysiological structure-to-function relationships, drug discovery and phenotyping.
imaging instrument
Imaging instrument
  • Components that generate the probing energy (such as electromagnetic radiation, ultrasound or electrical current)
  • The detector system
  • The tomographic image reconstructor (generally involves a mechanical or electronic scanning process and a variant of solving an inverse problem)
  • The image display (generally involves a computer terminal).
slide14
Novel ideas only survive if the environment for implementing the idea is present and/or the need is perceived.
slide15
PACS
  • Ultrasound
  • Magnetic Resonance Imaging
  • Computed Tomography
slide16
NMR
  • Lauterbur realized that the slight variation in magnet uniformity (the bane of spectroscopists) could be used to spatially localize the signal of interest and, hence, the controlled variation in magnetic field could form the basis of an imaging approach.
ultrasound microbubbles
Ultrasound microbubbles
  • Intravascular microbubbles were developed as an ultrasound contrast agent, but the harmonic frequencies generated which “contaminated” the Doppler signal used to measure their velocity became the basis of a great increase in specificity and sensitivity of the microbubble use in ultrasound.
chemical shift
Chemical shift
  • The paramagnetic effect of oxygen in the blood could be used to generate highly specific images of cerebral oxygen use and spectroscopic evaluation of metabolic events in tissues such as in the brain and heart.
positron emission tomography pet
Positron Emission Tomography (PET)
  • Measures radioactive traces injected into the body
reference
reference
  • Proceedings of the IEEE, Vol. 91, No. 10, October 2003, pp. 1483-1491.
basic concepts in image generation
Basic concepts in Image Generation
  • Spatial resolution
    • The number of pixels per image area
  • Contrast resolution
    • The number of bit per pixel determines the contrast resolution
  • Temporal resolution
    • A measure of the time needed to create an image
principle of echo scanners
Principle of Echo Scanners
  • In echo scanners, sound pulses are generated with frequencies of about a few MHz. These pulses are absorbed, scattered, or reflected in the patient. The reflections give rise to relatively strong echoes.
  • Reflections occur at interfaces between media that are different with respect to density and/or the velocity of sound (sound is reflected at interfaces with different acoustic impedances; the so-called acoustic impedance is equal to the product of sound velocity and density).
principle of echo scanners24
Principle of Echo Scanners
  • At an interface between soft tissue on one side and bone or air on the other side, a strong reflection is observed.
  • Scattering takes place if the dimension of the object is small (i.e., about the wavelength of the incident radiation). The beam is then scattered in all directions, and therefore, the amplitude of the signal detected by the transducer is relatively small.
principle of echo scanners25
Principle of Echo Scanners
  • The resolution of an echo scan, that is, the degree with which details located close together can still be distinguished, is determined by both the wavelength of the sound waves and the duration of the emitted pulse.
  • The pulse is usually several wavelengths long. In practice, therefore, reflections from two points separated by a few wavelengths can be discriminated.
  • The smaller the wavelength the better the resolution. Since the wavelength is inversely proportional to the frequency, the resolution is proportional to the frequency.
principle of echo scanners26
Principle of Echo Scanners
  • The attenuation coefficient (which expresses how much the beam is attenuated per centimeter of tissue because of scatter and absorption) is proportional to the sound frequency for soft tissue and is even proportional to the square of the frequency for other types of tissues.
  • The depth of penetration of the sound waves is inversely proportional to the frequency. The more the beam is attenuated, the more difficult it is to measure the reflections of deeper structures, since the signal-to-noise ratio gradually becomes smaller.
principle of echo scanners27
Principle of Echo Scanners
  • Since resolution and penetration depth pose contradictory requirements:
  • Deeper structures can only be visualized with relatively low frequencies, with a concomitant lower resolution.
  • The type of tissue influences the amount of absorption of the beam. Air and bone, for example, are strong absorbers, whereas muscle tissue and water hardly attenuate the beam.
principle of echo scanners28
Principle of Echo Scanners
  • At a frequency of 3 MHz (wavelength of 0.5 mm) depths of up to 10 cm are well visualized, with an axial resolution on the order of 1 mm.
  • For eye examinations a higher resolution is needed. In this case frequencies of between 5 and 13 MHz (wavelengths of between 0.25 and 0.075 mm, respectively) are used.
  • For brain examinations the sound beam must first pass bone structures (e.g., the tempora). Because of the high absorption of bone, especially for high frequencies, only low frequencies can be used, implying a lower resolution.
temporal
Temporal 太陽穴的,顳的
  • The space, on either side of the head, back of the eye and forehead, above the zygomaticarch and in front of the ear.
the 2003 nobel prize in physiology or medicine
The 2003 Nobel Prize in Physiology or Medicine
  • The Nobel Assembly at Karolinska Institutet awarded The Nobel Prize in Physiology or Medicine for 2003jointly to
  • Paul C Lauterbur and Peter Mansfield
  • for their discoveries concerning
  • "magnetic resonance imaging"
summary
Summary
  • Imaging of human internal organs with exact and non-invasive methods is very important for medical diagnosis, treatment and follow-up.
  • Seminal discoveries concerning the use of magnetic resonance to visualize different structures.
  • These discoveries have led to the development of modern magnetic resonance imaging, MRI, which represents a breakthrough in medical diagnostics and research.
slide32
Atomic nuclei in a strong magnetic field rotate with a frequency that is dependent on the strength of the magnetic field.
  • Their energy can be increased if they absorb radio waves with the same frequency (resonance).
  • When the atomic nuclei return to their previous energy level, radio waves are emitted.
  • These discoveries were awarded the Nobel Prize in Physics in 1952.
slide33
When the atom is placed in a magnetic field, the interaction energy -∙B of the spin magnetic dipole moment with the field causes further splittings in energy levels and in the corresponding spectrum lines.
slide34
During the following decades, magnetic resonance was used mainly for studies of the chemical structure of substances.
  • In the beginning of the 1970s, this year’s Nobel Laureates made pioneering contributions, which later led to the applications of magnetic resonance in medical imaging.
slide35
Paul Lauterbur (born 1929), Urbana, Illinois, USA, discovered the possibility to create a two-dimensional picture by introducing gradients in the magnetic field. By analysis of the characteristics of the emitted radio waves, he could determine their origin. This made it possible to build up two-dimensional pictures of structures that could not be visualized with other methods.
slide36
Peter Mansfield (born 1933), Nottingham, England, further developed the utilization of gradients in the magnetic field. He showed how the signals could be mathematically analysed, which made it possible to develop a useful imaging technique. Mansfield also showed how extremely fast imaging could be achievable. This became technically possible within medicine a decade later.
rapid development within medicine
Rapid development within medicine
  • A great advantage with MRI is that it is harmless according to all present knowledge.
  • The method does not use ionizing radiation, in contrast to ordinary X-ray (Nobel Prize in Physics in 1901) or computer tomography (Nobel Prize in Physiology or Medicine in 1979) examinations.
  • However, patients with magnetic metal in the body or a pacemaker cannot be examined with MRI due to the strong magnetic field, and patients with claustrophobia may have difficulties undergoing MRI.
especially valuable for examination of the brain and the spinal cord
Especially valuable for examination of the brain and the spinal cord
  • Today, MRI is used to examine almost all organs of the body. The technique is especially valuable for detailed imaging of the brain and the spinal cord. Nearly all brain disorders lead to alterations in water content, which is reflected in the MRI picture. A difference in water content of less than a percent is enough to detect a pathological change.
slide40
In multiple sclerosis 硬化症 , examination with MRI is superior for diagnosis and follow-up of the disease.
  • The symptoms associated with multiple sclerosis are caused by local inflammation in the brain and the spinal cord.
  • With MRI, it is possible to see where in the nervous system the inflammation is localized, how intense it is, and also how it is influenced by treatment.
slide42
Another example is prolonged lower back pain, leading to great suffering for the patient and to high costs for the society.
  • It is important to be able to differentiate between muscle pain and pain caused by pressure on a nerve or the spinal cord.
  • With MRI, it is possible to see if a disc herniation is pressing on a nerve and to determine if an operation is necessary.
improved diagnostics in cancer
Improved diagnostics in cancer
  • MRI examinations are very important in diagnosis, treatment and follow-up of cancer.
  • The images can exactly reveal the limits of a tumour, which contributes to more precise surgery and radiation therapy.
  • Before surgery, it is important to know whether the tumour has infiltrated the surrounding tissue.
  • MRI can more exactly than other methods differentiate between tissues and thereby contribute to improved surgery.
slide44
MRI has also improved the possibilities to ascertain the stage of a tumour, and this is important for the choice of treatment.
  • For example, MRI can determine how deep in the tissue a colon cancer has infiltrated and whether regional lymph nodes have been affected.
magnetic resonance imaging
Magnetic Resonance Imaging
  • The aim of MRI is to provide an image of the tissue distribution in a plane through the body, for example, by measuring the hydrogen density in that plane.
  • The idea is, once again, to obtain a two-dimensional image of a two-dimensional slice through the body.
principle of magnetic resonance imaging
Principle of Magnetic Resonance Imaging
  • How can the density of hydrogen nuclei at each location of interest in the body be obtained?
  • The hydrogen atoms at each location have their own specific Larmor resonance frequency, depending on the local strength of the external magnetic field.
principle of magnetic resonance imaging47
Principle of Magnetic Resonance Imaging
  • By irradiating the body with EM radiation at a certain frequency in a direction perpendicular to the external magnetic field, only those hydrogen nuclei that have a Larmor frequency equal to the frequency of the RF excitation pulse will resonate.
  • The Larmor frequency depends on the strength of the magnetic field, so these nuclei are located in a small volume.
principle of magnetic resonance imaging48
Principle of Magnetic Resonance Imaging
  • The RF excitation pulse has such a duration that after the pulse the magnetization vector will process perpendicularly to the external magnetic field (the 90o RF pulse).
  • A current is then induced in a coil perpendicular to the external magnetic field. This current has an amplitude proportional to the number of the resonating nuclei in that volume and a frequency equal to the Larmor frequency.
principle of magnetic resonance imaging49
Principle of Magnetic Resonance Imaging
  • This frequency determines the position of the sampled volume. This procedure is repeated with other frequencies for all volumes with a specific Larmor frequency.
  • By this procedure the density of hydrogen nuclei can be obtained at all locations of interest.
principle of magnetic resonance imaging50
Principle of Magnetic Resonance Imaging
  • The external magnetic field consists of two parts:
    • a strong homogeneous field
    • a smaller magnetic field, of which the strength changes linearly in a certain direction. The linearly changing field can be applied in three directions by three orthogonally placed gradient coils. This changing magnetic field is also called the magnetic field gradient.
slide51
If the field gradient is directed, for instance, from head to toe, every transverse slice in the patient resonates at a different Larmor frequency.
  • RF coils may be used to detect the resultant magnetization changes, also called receiving coils.
principle of magnetic resonance imaging52
Principle of Magnetic Resonance Imaging
  • All nuclei in a slice orthogonal to the gradient direction will experience the same external magnetic field strength and therefore will have the same Larmor frequency (this gradient is called the slice selection gradient).
  • The amplitude of the current in the receiving coil after the application of a 90o RF pulse will be proportional to the total number of hydrogen nuclei in this slice.
slide53

The phenomenon of spins aligning themselves to an external magnetic field.

At 0 K all spins are aligned when an external magnetic field is present (a);

when no external magnetic field is present the spins will point in all directions (b);

at room temperature only a small part of the nuclei will align themselves: 1 per million (c)

at a field strength of 0.1 tesla

and 5 per million (d) at a magnetic field strength of 0.5 tesla

(after Philips).

Figure 9.11

tesla
Tesla
  • The units of B is the same as the units of F/qv.
  • The SI unit of B is equivalent to 1 N.s/C.m
  • 1 tesla = 1 T = 1 N/A.m
  • Another unit of B, the gauss (1G = 10-4 T)
principle of magnetic resonance imaging55
Principle of Magnetic Resonance Imaging
  • more position selectivity is attained as follows.
  • after the 90o RF pulse, the slice selection gradient is switched off and another magnetic field gradient is applied orthogonally to the direction of the slice selection gradient (this additional gradient is called readout or measurement gradient, because it is applied after the 90o pulse and just before the induced current is measured in the receiving coil) the frequency of the resonating nuclei will change:
slide56
nuclei in the slice located along different rows orthogonally to the readout gradient direction will experience a different external magnetic field strength (the sum of the first homogeneous field and the readout gradient field) and therefore will have different Larmor frequencies in the different rows.
principle of magnetic resonance imaging57
Principle of Magnetic Resonance Imaging
  • This means that each row of hydrogen nuclei in the slice induces a current with a different frequency in the receiving coil. The amplitude of the component with a certain frequency, again, is proportional to the number of hydrogen atoms along the corresponding row, and the frequency now determines the position of the corresponding row.
slide58

Precession of magnetization under the influence of an external magnetic field

with strength Bo and an oscillating field B1

(due to electromagnetic radiation) during a 90 RF pulse as seen from the observer (A)

and as seen from the standpoint of the rotating field (B) (Philips).

Figure 9.12

principle of magnetic resonance imaging59
Principle of Magnetic Resonance Imaging
  • Since the sum of signals with all of these different resonance frequencies is detected simultaneously, a Fourier transformation needs to be conducted to obtain amplitude and position information in the specific frequency spectrum.
  • Each frequency corresponds to a row in the slice. The amplitude of each frequency component is proportional to the number of resonating nuclei in a certain row.
principle of magnetic resonance imaging60
Principle of Magnetic Resonance Imaging
  • The frequency spectrum corresponds to a profile representing the number of hydrogen nuclei in each row as a function of the location along the direction of the readout gradient.
  • By measuring the profile for different directions of the readout gradient and using a back-projection technique, the distribution of the hydrogen nuclei over the slice can be obtained.
  • The procedure can be sped up by applying a second field gradient orthogonally to the readout gradient before the latter is applied and by using the resulting phase differences.
principle of magnetic resonance imaging61
Principle of Magnetic Resonance Imaging
  • After termination of the 90o RF pulse, the magnetization gradually returns back to its equilibrium position, which is parallel to the external field. This phenomenon is called relaxation.
slide62
Two types of relaxation
    • relaxation caused by energy exchange with the surrounding nuclei (called the lattice). This so-called spin-lattice relaxation or longitudinal relaxation is characterized by the so-called longitudinal relaxation time, T1, which is defined as the time that is required for 63% of the nuclei to realign themselves with the external field.
    • The second form is the relaxation due to spin-spin interactions. Spin-spin relaxation is characterized by the transverse relaxation time, T2, which measures the time after which the transverse component has decreased by 63%.
larmor frequency
Larmor Frequency
  • In physics, Larmor precession, named after Joseph Larmor refers to the precession of the magnetic moments of electrons, atomic nuclei, and atoms around the direction of an external magnetic field.
  • The magnetic field exerts a torque on the magnetic moment,
  • Γ= μX B = γJ X B
  • where Γ is the torque, J is the angular momentum, B is the external magnetic field, X is the cross product, and γis the gyromagnetic ratio which gives the proportionality constant between the magnetic moment and the angular momentum.
larmor frequency64
Larmor Frequency
  • If we consider the case of a static magnetic field,

B = B0 z

  • we find that the angular momentum vector J precesses about the z axis with an angular frequency known as the Larmor Frequency,

ω0 = γB

  • producing a gyroscopic motion, much like the spinning of a top.
larmor frequency65
Larmor Frequency
  • It should be noted that in the above discussion we used the total electronic angular momentum vector J,
  • but the equations above hold equally well for spin angular momentum of the electron S,
  • the orbital angular momentum of the electron L,
  • the spin angular momentum of the nucleus I,
  • or the total angular momentum of the atom F.
slide66
The gyromagnetic ratio is in general different for each type of angular momentum that may be considered, but using the following formula we may find the factor of interest.

γ= gμB / h,

  • where g is the appropriate Lande g-factor, μB is the Bohr magneton, and h is the reduced Planck\'s constant. For an electron, the gyromagnetic ratio is approximately 2.8 MHz / Gauss.
slide67
A famous 1935 paper published by Lev Landau and Evgeny Lifshitz predicted the existence of ferromagnetic resonance of the Larmor precession, which was verified experimentally by J. H. E. Griffiths in 1946.
computed tomography
Computed Tomography
  • Consider a cross section through the body of a patient with a thickness of about 1 mm. Now, divide the cross-section into a large number of small squares, each with an area of about 1 mm2. When a narrow X-ray beam, a so-called pencil beam, passes through the slice, each square through which the beam passes attenuates it to a certain extent.
computed tomography69
Computed Tomography
  • The amount of attenuation is determined by the molecular composition and the density of the tissue present in the square.
  • The intensity of the eventually transmitted beam will be smaller than the intensity of the incident beam. The intensity reduction is caused by all the squares through which the beam passes.
  • Each square may attenuate the beam differently because of the presence of different tissue.
computed tomography70
Computed Tomography
  • To measure the attenuation of a beam, it is necessary to use a combination of an X-ray tube and a detector.
  • The absorbing tissue slice is located between them. The X-ray tube produces a pencil beam of known intensity and the detector measures the intensity of the transmitted beam.
  • the combination of X-ray tube and detector (mounted into the so-called gantry) can both be shifted along a line ("translated") and rotated (see Fig. 9.6).
slide71

Principle of computed tomography.

The combination of X-ray tube and detector is translated across the patient,

producing a density profile p(k, f).

By rotating the X-ray tube-detector combination,

a number of profiles will be obtained.

From these profiles the attenuation coefficients of each pixel can be determined.

Figure 9.6

computed tomography72
Computed Tomography
  • by displaying the attenuation coefficients (the values indicating the amount of absorption per millimeter) we can obtain an anatomical image, we must be able to determine the attenuation coefficients of each square separately.
  • From one measurement it is not possible to deduce how much each separate square attenuated the beam. Yet, determination of the attenuation of each square in the cross-section is the purpose of the procedure.
computed tomography73
Computed Tomography
  • Since one pencil beam covers only one row of squares, we must translate the beam over a distance equal to its width. In this way we can take into account the attenuation coefficients of the squares located on a neighboring row. After measuring the transmitted intensity, the procedure is repeated by translating the beam and measuring the transmitted intensity until we have covered the total cross section.
slide74
It is still not possible, however, to determine the individual attenuation coefficient of each square from these data; for each position of the beam we obtain the total attenuation due to the attenuation caused by all squares that are passed by the pencil beam.
computed tomography75
Computed Tomography
  • What we have obtained is an intensity profile (and, therefore, a measure of the total attenuation) of the transmitted beam as a function of the position of the beam.
  • Each point in the profile indicates how strongly the incident beam was attenuated by the row of squares that was passed by the beam in that position (Fig. 9.6).
  • we repeat the procedure outlined above for various angles of the beam. It is possible to compute the attenuation per square from these data.
slide76
an X-ray beam is attenuated in an exponential way, depending on the length of the path and the attenuation coefficients of the squares, denoted here as pixels encountered along its path. If we assume that the attenuation coefficient is constant over the whole pixel and if we represent the attenuation of pixel i by the attenuation coefficient mi, then the intensity of the transmitted beam (I) can be related to the intensity of the incident beam (I0) in the way represented in Fig. 9.7.
slide77
If we take the natural logarithm of the ratio of I and I0, we obtain the following relation for each pixel:
  • In(I/I0) = ∑i=1N dimi
slide78

The intensity of the transmitted beam as a function of the attenuation coefficient

of the pixels traversed.

Upper part, the intensity after crossing one volume element;

middle part, after traversing n volume elements; lower part, the analog case.

Figure 9.7

slide79
Here, di is the length of the path that the beam traversed through each pixel i, and mi is its attenuation coefficient.
  • We have obtained an equation with, to the left, the measured intensity ratio and, to the right, N unknown quantities: the coefficients mi. Since the geometry of the beam and the cross-section are known, the length of the path di traversed through each pixel is also known.
slide80
The number of unknown quantities therefore only increases. After the beam has covered the whole cross section, the equations contain as many unknowns as there are pixels in the cross section. By turning the gantry over a small angle and repeating the earlier procedure we obtain another intensity profile.
slide81
The attenuation coefficients of the pixels remain the same, but the length of the paths traversed through each pixel has changed. In this way we obtain new equations with the same number of unknowns. By measuring the intensity profiles at enough angles we can, in principle, obtain as many equations as there are unknowns.
slide82
As can be seen from Fig. 9.8, a visualization of the values of the attenuation coefficients by way of grey values indeed produces an anatomical image.
  • The procedure of CT as explained here is not used in practice, because it would be too time-consuming, but it provides a good insight into the principles of CT.
  • In practice, back-projection algorithms are used, since these are more efficient.
slide83

Example of cross-sections through several parts of the body:

skull, thorax, and abdomen, obtained by computed tomography.

Figure 9.8

slide84
Back projection is one of the techniques that is used in practice to obtain the attenuation coefficients mi.
  • This technique can be used when intensity profiles that cover the total cross section under various angles are available. In an individual profile, each point represents the amount of attenuation by the pixels transmitted by the beam.
slide85
Figure 9.9shows the intensity profiles that result from a single attenuating pixel. Each profile shows a dip at the location where the beam passed through this pixel.
slide87
Upper left, density distribution of a point absorber along a line through the object; lower left, the resulting intensity profiles; lower right, the back- projection; upper right, reconstructed density distribution on a line through the object (after Philips).
slide88
If we have only one intensity profile we cannot determine where on the path the pixel was located. We cannot even decide whether the absorption was due to a single pixel or was due to an attenuating medium that was present over the whole path.
  • The only inference that we can make is that the attenuating medium was present only along one line in the cross section, since the intensity profile showed a dip at only one point.
slide89
The back-projection method starts with the assumption that the absorbing medium is uniformly distributed over the line. Of course, this may be incorrect, but it will be demonstrated that the errors resulting from this assumption can be corrected.
  • If we have several intensity profiles obtained at different angles, we get a reconstructed image, as shown in Fig. 9.9.
  • The reconstruction has a star-like distribution. By increasing the number of angles, the intensity in the center will increase much faster than the intensity at the periphery.
slide90
With the use of more angles, the back-projected image becomes more similar to the actual one, only it is less sharp; instead of an image showing one attenuating pixel, the neighboring pixels are visible in the reconstructed image as well. This blurring effect can be corrected to a certain extent by using appropriate filtering techniques, resulting in a sharper image. Since a real cross section can be considered a union of cross sections, with each one containing only one attenuating pixel, the back-projection technique can also be applied to real patient cross sections. The back-projection technique can also be used in MRI (magnetic resonance imaging) and SPECT (single photon emission computed tomography).
slide91
It appears that the attenuation coefficient is characteristic for the type of tissue (or more correctly, the chemical composition of the tissue), as is apparent from Fig. 9.10.
  • When the values of the attenuation coefficients of the pixels are displayed on a monitor in the form of grey values, the result consists of anatomical images that can be directly interpreted.
hepatic surgery simulation
Hepatic surgery simulation
  • Creating a simulator for training physicians to perform minimally invasive surgical procedures
slide97

Figure 2. Extraction of the hepatic parenchyma (parts a and b), the vascular trees and hepatic lesions (parts c and d) from a CT scan image.

slide99
Figure 3b. Sequence of a simulated liver resection that includes the clipping and cutting of the portal vein.
figure 1 a user interface for the virtual colonoscopy system courtesy of viatronix inc
Figure 1. A user interface for the virtual colonoscopy system (courtesy of Viatronix, Inc.).
slide102

Figure 2. Endoscopic view of painted information after an antegrade flythrough (left); and an example of a missed patch after both antegrade and retrograde flythroughs (right). The green areas were visualized, while the reddish areas were missed.

figure 3 a volume rendered surface view left and an electronic biopsy right of a polyp
Figure 3. A volume-rendered surface view (left) and an electronic biopsy (right) of a polyp.
spamm spatial modulation of magnetization
SPAMM: SPAtial Modulation of Magnetization
  • A magnetically tagged MRI technique
  • Advantage: a number of material points within the myocardium walls can be marked noninvasively and tracked, providing the true 3D motion of the heart muscle over time.
slide106

Figure 1. The essential data needed (boundaries and tag lines) from each MRI-SPAMM short-axis image: (left) End-diastole short-axis view; (right) Mid-contraction short-axis view.

slide107
Figure 2. Sample results from the automated boundary detection algorithm for the LV and RV and inflow and outflow tracts of the RV.
slide109
Figure 3. The top row shows the estimation of the LV-RV endocardium and the epicardium on the MRI-tagged slices for a normal heart. The second row shows a normal and an abnormal heart at end-diastole. The RV endocardium of the RV hypertrophy patient is significantly larger than that of normal heart: (a) Normal heart (b) RV hypertrophy heart. The third row shows the heart model\'s motion during systole. Finally, the fourth row shows a finite element model of the ventricles derived from MRI, with local fiber angles (blue) derived from in vitro data superimposed at corresponding locations in (left) subendocardium and (right) subepicardium.
slide112
Figure 1. a) Automated segmentation of temporalis muscle: (1) color VH Male slice, (2) a fuzzy connected component, (3–5) iterations of the VD-based algorithm, (6) an outline of the boundary; b) 3D segmentation of the left kidney: (1) input data, (2) fuzzy connectedness, (3, 4) VD classification (5) deformable model, (6) hand segmentation. c) 3D segmented and visualized left kidney derived from the Visible Human Male data set—3D models of: (1) fuzzy connectedness, (2) Voronoi Diagram classification, (3) deformable model, (4) hand segmentation.
slide113

Figure 2. Foot anatomy: a) flexor muscles (oblique view), b) all the structures (oblique view), c) a "reference" 3D model (plantar view), d) corresponding medical illustration based on the model in c).

slide117
Figure. Examples of medical image segmentation and registration algorithms available in ITK: a) Functional MRI fused with MR angiography using landmark initialized mutual information registration (courtesy of UNC); b) 2D to 3D registration of angiography data (courtesy of the Imperial College of London); c) Inner-ear segmentation of the cochlea and vestibular system using fast-marching level-set methods (courtesy of Kitware); d) Eyes, muscles, and optic nerves of the Visible Human Project data using interactive color watershed segmentation (courtesy of the University of Utah).
the visible humans project
The Visible Humans Project
  • The goal of the Visible Humans project, sponsored by the U.S. National Library of Medicine, is to provide image data sets of the human body for use in the study of anatomy, for use in conducting imaging research, and for use in a wide range of educational, diagnostic and treatment planning and simulation applications.
the visible humans project119
The Visible Humans Project
  • The first phase of the project has resulted in CT, MRI, and cryosection image sets for a human male and a human female.
  • The complete male data set consisting of scans taken at 1 mm resolution is 15 gigabytes in size.
  • The complete female data set consists of scans taken at 0.33 mm intervals and is 40 gigabytes in size.
  • Both datasets may be downloaded over the Internet by interested individuals for research and experimentation.
slide121
Reconstruction of a sagittal cross section and a few horizontal cross sections through one of the visible humans
slide123
Example of 3-D presentation of the chest after boundary detection, labeling, shadowing and coloring of organs
volume rendering
Volume rendering
  • The process of creating a 2D image directly from the 3D volumetric dataset of voxels.
  • Voxel: Short for volume pixel, the smallest distinguishable box-shaped part of a three-dimensional image.
reference125
Reference
  • Communications of the ACM, February 2005, Vol. 48, No. 2.
ad