Computer Imaging & Sciences :Computer Imaging & Sciences Claudy-Ann Rigaud David Ponton Gabriel Leiba Mercedes Gonzalez


Objectives :Objectives Describe image processing operations Discuss a nine point smooth for a 3x3 matrix Explain image ROI placement and curve generation List the principles of normalization and discuss normalized background-corrected counts Describe frequency space representation of images Discuss the principles of SPECT and PET reconstruction Explain the use of frequency space filters to remove noise from SPECT and PET images Diagram compute network configurations Discuss uses for non-imaging computers Define the internet and discuss nuclear medicine applications


Imaging and processing :Imaging and processing Gamma-ray scintillation events that happen at specific detector location are stored as digital images by accumulating gamma-ray counts Sometime the software and display screen allow images to be displayed as the black on white or white on black The human eye can differentiate fewer than 100 shade of gray Most computers system generates an 8 bit image assigning display intensities from 0-255.


Imaging and processing (cont) :Imaging and processing (cont) The maximum pixel count is display intensity of 255 Some display system are assigned only 64 shades of gray which is sufficient for viewing The relationship between the number of counts and display intensity most of the time are linear Most computers allow a logarithmic and exponential relationship between the count and the intensity


Color vs. Gray scale :Color vs. Gray scale


Color scale applied :Color scale applied


Imaging and processing (cont) :Imaging and processing (cont) The logarithmic assigns more gray levels to low count pixels and compresses the number of shades of gray assigned to high pixels. Background subtraction is another enhancement technique, background enhancement selects a counts threshold that is set to the lowest intensity and reassigns intensities between the threshold and the maximum pixel count. Color is another technique used to enhance the image. Red, green and blue guns of the CRT can be assigned intensity values from 0-255 and can be mixed to generate more than 16 million colors. Most effective color table are those that have gradual and continuous shades of color. Another common used table is the “hot iron" table, assign gray scales from black to dark red through orange and white for the hottest pixel values.


Image algebra :Image algebra Simplest image processing operations are the mathematical operations of addition, subtraction, multiplication and division. Image addition is performed to improve the count density of images or to compress a sequence of dynamic images into smaller number of frames. Subtraction is mostly used in image matrix in two ways: subtraction of numeric valve from all pixels and subtraction of one image from another. Subtraction of a number from pixel count from each pixel if an image is used to perform background subtraction as an alternative to grayscale enhancement. Another simple image manipulation is performed to shift an image a number given of pixels in the x or y direction or to rotate an image about its center point to correct alignment.


IMAGE SMOOTHING :IMAGE SMOOTHING Image smoothing is used to reduce noise from the random effects of radionuclide counting. Simplest technique is average the counts of a given pixel with that of its eight surrounding neighbors and replace the center pixels count with the new table. The simplest and most common one is the nine-point smooth, which is a filtering technique to modify a specific pixel value according to the values of its neighbors. The nine-point smooth uses a 3 × 3 matrix centered over each pixel in the image. Nine point smoothing blends each pixel value with those neighbors, creating a smoother, more aesthetic image.


Image Smoothing (cont) :Image Smoothing (cont) This smoothing results in a loss of resolution, and detail is somewhat blurred Filters with negative values around the edges can enhance or sharpen the edges of organs. Filtering dynamic image sets can use a temporal filter; it performs weighted averaging of an image with those that occur just before and after a dynamic image sequence. Temporal filtering is applied mostly to gated cardiac images with the filter applied in a close loop. The difference between nine point and temporal filtering is that temporal filtering removes the noise without a loss of spatial resolution


Cinematic display :Cinematic display Dynamic sequence of images may be displayed as a continuous-loop movie known as a cinematic display Images that need to be displayed are formatted into an area of memory called buffer so that the image could be retrieved quickly Some systems may have insufficient memory and a display buffer is created on a disk Dynamic studies, gated blood pool image and SPECT images can be displayed on cinematic mode. Longer dynamic studies, such as 30 min kidney studies can display to compress the set of images into a few seconds.


Image Quantitation :Image Quantitation Digital nuclear medicine images are many times acquired to derive quantitative information Counts in a particular area can be extracted from the image by defining a region of interest (ROI)


ROI :ROI When defining a ROI, the area being defined should be physiologically meaningful Some clinical programs now perform automated ROI definition by doing math to identify the edge of an organ Different information can be extracted from the images depending on how the ROI has been defined


ROI manipulation :ROI manipulation Some nuclear medicine systems allow ROI’s to be manipulated just like images so as to add or subtract regions. Ex. A region defining the renal pelvis can be subtracted from a region defining the whole kidney which leaves the area of the renal cortex


Curves :Curves The information that we get is derived by setting a ROI and obtaining the ROI counts The ROI counts in sequential images from a dynamic study can be used to plot the radioactivity-versus-time change or time-activity curve


Curves :Curves Curves provide useful information in evaluating the accumulation and washout of radiopharmaceutical from the kidney, changes in the left ventricular volume on gated studies and changes in radionuclide distribution on gastrointestinal studies


Curves :Curves The appropriate scale of each axis should allow the observer to view most accurately changes of clinical significance in the study Because of statistical limitations in counts it is sometimes helpful to smooth curve data Another technique to reduce noise in curve data is to fit curve points to a mathematical formula that allows additional quantitative information to be derived


Normalization :Normalization Normalization is a concept that implies that a measurement has been brought to a standard Ex. Two images with different maximum counts may have their intensities normalized The two images would be displayed with the same maximum intensity Normalization is most commonly applied to two ROIs or curves


Normalization :Normalization Region normalization is most commonly done to subtract the background counts of one region from the counts of a different sized region


Emission Computed Tomography Imaging :Emission Computed Tomography Imaging Emission Computed Tomography(ECT) is a general term describing the reconstruction of three dimensional image volumes that are derived from one of two techniques: Single Photon Emission Computed Tomography(SPECT) or Positron emission tomography(PET)


SPECT :SPECT SPECT imaging is done by obtaining planar images with the scintillation camera from many angles around the patient. Images are acquired from 360 degrees around the patient, except in myocardial perfusion where only 180 degrees are acquired


SPECT :SPECT The planar projection images are first viewed cinematically to ensure that no significant patient motion has occurred Image data is then back projected to overlay areas of increased activity and create a transverse slice image Back-projection produces a streak from where multiple data sets are laid on top of each other Filtered back-projection reduces the streak artifact


PET :PET PET information is created from lines drawn between two individual detectors, in a ring of detectors around the body that simultaneously detect a pair of photons that result from a positron decay All the lines measured from various directions provide information about the distribution of the radiotracer within the body. Using reconstruction techniques similar to SPECT, 3-D PET images are then created


Frequency Space And Filtering :Frequency Space And Filtering In SPECT reconstruction images are represented by a group of frequencies. This is done by plotting the frequency on the horizontal axis and the wave amplitude on the vertical axis. We use frequency space Filters to reduce noise and to try to obtain a clear picture of an organ or object. These filters are mathematical formulas that generate the curve shape.


Frequency :Frequency The amplitude of the waves are on the (y-axis). This represents the height or number of counts of the wave. While, the wave length (x-axis) represents the space in which the wave travels. Example: 0.5 cm /0.6cm Fourier Transform is a mathematical equation used to convert an image into its wave components. Inverse Fourier transform returns waves back into picture mode. When our images are in frequency space mode, they are seen as a group of low and middle frequency waves, thus; the high pitches are just noise in the background. All we need now is a filter to let us identify and define our picture.


Image filter process :Image filter process


Filters :Filters Filtering is the reduction of noise. Once we have picked up the raw frequency we need to add a mathematical formula that will multiply to give us a reduced amplitude of the wave. Filters multiply the high frequencies by low values or by zero thus; a good amount of noise is reduced. The most common filters are the Ramp, von Hann, Butterworth, Parzen, Hamming, Wiener and Metz. Remember: filtering will always reduce the quality of the image. We must balance noise reduction with resolution. Low pass filters with a high cutoff frequency will produce a high resolution but it will contain a lot of noise.


Filtering and Tomographic Reconstruction :Filtering and Tomographic Reconstruction In SPECT reconstruction, the image is usually filtered twice. The image is pre filtered to remove noise from the planar projection image then, the image is filtered again during the reconstruction algorithm. For example: a SPECT image of the liver requires smooth slices, because abnormalities are seen as cold defects in a uniform area of pharmaceutical.


Iterative Reconstruction Algorithms :Iterative Reconstruction Algorithms Incorporates a lot more information than filtered images, it consist in computing a series of 3D images to picture activity. These images have a better resolution than filtered images and makes the edges of organs look sharp with good image contrast. There are 4 specific categories of Expectation Maximization : Maximum Likely hood (ML), Expectation Maximum (EM), Maximum a Priority (MAP) and Ordered Subset Expectation Maximization (OSEM). OSEM evaluates subgroups of the projections in order to calculate the 3D volume more quickly than calculating values in every pixel in a projection. Meaning little post reconstruction filtering would be needed on these images. These images do not have the streak artifacts that are produced by back-projection algorithms.


Three-Dimensional Display :Three-Dimensional Display 3D display uses two techniques: surface display and volume rendering for 3D viewing. 3D Display is more useful for heart and brain cortex viewing because it only displays a solid outer surface of the organ. This display is specially good for thin organs with cold abnormalities. Volume rendering provides a translucent appearance to a 3D volume. This is achieved by projecting an image’s volume into planar images from multiple directions around the object volume like the original planar images. In this reprojection, we select the maximum pixel count along each projection line that would be seen in an individual pixel. This produces an image with a translucent appearance and with very little noise. This technique is useful for finding hot lesions on bone SPECT and identifying hepatic hemangiomas.


Clinical Applications :Clinical Applications Clinical applications designed specifically for use in the hospitals are written using one of the following programming languages: C - Programming language that is popular and widely used for creating computer programs, in which lists of instructions are created for a computer to follow. Macro protocol - A macro is a chain of simple computer operations that are combined to form a practical and meaningful method of evaluating image data.


A simple macro can be written to perform the following tasks: :A simple macro can be written to perform the following tasks: image normalization subtraction of two images adding frames in a dynamic study image displays adding frames of a flow study setting ROI’s generating curves subtracting normalized background displaying curves performing calculations


Workstations :Workstations Image viewing is most conveniently handled on a multitasking workstation with a graphical user interface. Graphic workstations usually have a large screen for displaying both images and text. Having several windows opened on the screen, allows the technician simultaneously display a study in one window, perform SPECT reconstruction in another window, and in a different window perform data archiving.


Nonimaging Computer Applications :Nonimaging Computer Applications Some personal computer applications perform common business activities in the nuclear medicine field. The following programs have a variety of administrative and patient applications: Word processing Accounting Spreadsheets database management Programs for patient scheduling and generating reports of patient studies are also available.


Nonimaging Application :Nonimaging Application Nuclear pharmacy calculations and records can be automated, and accurate records can also be kept using commercially available database programs.


Networking of computers in nuclear medicine has become common and is also important asset to the clinic. With the connection of two or more computers, the transfer of images and programs can be performed with ease. :Networking of computers in nuclear medicine has become common and is also important asset to the clinic. With the connection of two or more computers, the transfer of images and programs can be performed with ease. Connects several computers to a larger central host computer for sorting and processing all data, sometimes using more than one processing terminal for image manipulation and display. Connects several computers along a single communications line. Each computer has a unique name, and the destination computer is specified when transferring files. Host networking Bus network.


Networks :Networks


Picture Archiving and Communications System :Picture Archiving and Communications System In most departments all nuclear medicine images are acquired digitally and are transferred from one system to another. Physicians view and interpret images directly from the computer screen, eliminating the need for film. This system is called a picture archiving and communications system (PACS). The filmless nuclear medicine department should have hardware and procedures in place to allow archiving of image data, a backup copy of these data, and enough storage capacity to keep many patient studies available for immediate retrieval.


Digital Imaging and Communications in Medicine :Digital Imaging and Communications in Medicine There are advantages to being able to move images from various cameras to other computers for viewing, and this transfer of images is easier if both cameras speak the same “file” language. Software is available from all computer vendors to convert and transfer images using DICOM. Therefore, DICOM is the common image file format used in PACS systems to distribute images throughout the healthcare system.


The Internet :The Internet An “information superhighway” that can simply be described as a network of networks. The organization of computers on the internet is controlled by an addressing system. Data files that are transferred on the internet are broken up into small, manageably sized data packets that may actually be routed in different directions on the internet but arrive and are recognized into their original format at their destination. The most rapidly expanding part of the internet is the World Wide Web. The WWW is based on hypertext documents, which provide text, image, video, and sound files. A hypertext document is written in a special format language called hypertext markup language (HTML).


Nuclear Medicine & the Internet :Nuclear Medicine & the Internet Often nuclear medicine computers may not be connected to the internet because of the concern over security issues, such as unauthorized access to sensitive patient information. However, they may be protected behind a firewall to prevent outside access. A nuclear medicine department could create a Web server with documents relevant to its research, continuing education programs, or teaching files. Examples: Washington University in St. Louis http://gamma.wustl.edu/home.html University of Kansas http://www.rad.kumc.edu/nucmed/


Summary :Summary Gamma-ray scintillation events that happen at specific detector location are stored as digital images and displayed on a high resolution monitor. The nine-point smooth 3 × 3 matrix is the most common filtering technique. When defining a ROI, the area being defined should be physiologically meaningful Normalization is a concept that implies that a measurement has been brought to a standard SPECT imaging is done by obtaining planar images with the scintillation camera from many angles around the patient. PET information is created from lines drawn between two individual detectors, in a ring of detectors around the body that simultaneously detect a pair of photons that result from a positron decay Frequency space Filters are used to reduce noise and to try to obtain a clear picture of an organ or object. Networking allows reliable communication between systems. Nonimaging computer applications are used in a variety of ways in nuclear medicine The internet is an “information superhighway” that can simply be described as a network of networks. It is useful to transfer hypertext image documents.


References :References Christian, Paul E., and Kristen M. Waterstram-Rich. Nuclear Medicine and PET/CT Technology and Techniques. 6th. St. Louis: Mosby Elsevier, 2007. Marshall, Brian. "How C Programming Works ." How Stuff Works. 2008. 13 Sep 2008 . "CDW Healthcare." CDW-G. 2008. CDW Corporation. 15 Sep 2008 .


Q&A :Q&A What is the most common type of image smoothing? The 9-point smooth The 5-point smooth The Smoothie King® None of the above


Slide 45:2. How many shades of gray can the human eye differentiate? A. 625 B. 53 C. 100 D. 394


Slide 46:3. What is an ROI? A. Radiation overload interface B. Roentgen over intensity C. Region of Interest D. All of the above


Slide 47:4. A concept in Nuclear Medicine that implies that a measurement has been brought to a standard A. Normalization B. Desalinization C. Cauterization D. None of the above


Slide 48:5. SPECT stands for: A. Single photon emission computed tomography B. Side proton engine calculator transformer C. Scattered particle energy collision technology D. All of the above


Slide 49:6. SPECT is used to render 3-D images. A. True B. False


Slide 50:7. What is the purpose of the filter? A. To reduce noise B. To obtain a clearer image C. Both A & B D. None of the above


Slide 51:8. What does PACS stand for? A. Photon acquisition and Compton scattering B. Picture archiving and communication system C. Proton acquisition and Compton scattering D. Pixel archiving and camera system


Slide 52:9. DICOM is the common image file format used in PACS systems to distribute images throughout the healthcare system. A. True B. False


Slide 53:10. Why wouldn’t nuclear medicine computers be connected to the internet? A. It is impossible to post certain acquisition files on the internet B. There may be unauthorized access to patient data C. There are certain security issues D. Both B and C


Answers :Answers 1. A 2. C 3. C 4. A 5. A 6. A 7. C 8. B 9. A 10. D