Digital Computers in Nuclear Medicine :Digital Computers in Nuclear Medicine Matty Smith-Lee Alex Ramos David Ponton


Objectives :Objectives Discuss the basic elements of a computer List non-imaging applications Describe computer memory, CPU, and Input/output devices Explain Digitization Detail the operation of a computer Discuss the digitization of analog data Describe the parameters of digital images Explain the acquisition of digital data


Objectives :Objectives Discuss static images Discuss dynamic study Discuss gated study Explain reconstruction of Images Discuss Superimposition and Subtraction of Images Discuss display monitors Discuss software and DICOM Explain PACS


Basic elements of a computer :Basic elements of a computer (CPU)- Central Processing Unit Memory – RAM / ROM External Storage Floppy, Zip Drive CD/DVD- ROM Flash Drive Input/output Devices Keyboard Monitor Printers Video Monitors


Non-imaging applications :Non-imaging applications Patient Scheduling Record Keeping Archiving Inventory of Supplies Quality Control Log Budget Management


Operation :Operation Electrical pulses are obtained in analog form and are then digitized Digital Binary Code (0,1) , represent on and off 1 Byte= 8 bits or 255 units of information 1 Word= 2 Bytes= 16 bits In newer computers, 32 to 64 bits Loss of signal information as digitization takes place


Central Processing Unit :Central Processing Unit Performs all control, logic, and arithmetic operations Executes Programs Set of instructions Transfer of data is performed by the CPU Faster CPU, less time for processing Multiple applications simultaneously


Computer Memory :Computer Memory RAM- Random Access Memory Temporary storage of data Write and Read capacity Data is lost when computer is shutoff ROM- Read Only Memory Permanent storage of data CD-ROM’s (650-700Mb) and DVD-ROM’s (4.7Gb) External Storage


Input / Output Devices :Input / Output Devices Input Devices Mouse Keyboard Touch screen Output Devices Persistence Screen LCD Printer


Digitization :Digitization (ADC)- Analog to Digital Converter Analog signal are continuous in time Digital signals are a sample of time points of the analog signals Data is lost through this process Higher bit ADC’s prevent this loss by producing a large number of bits from each analog signal Faster ADC for higher count rates Slower ADC for low count rates(increased dead time)


Operation of A Computer :Operation of A Computer Operates according to instructions provided by the operator Instructions are given in the form of programs Most important program is the operating system Data is provided as input for processing in the form of counts or pulses Data is processed according to the computers software and then either: Stored in computer memory Stored in external memory Displayed on a computer monitor Sent to an output device such as a printer for hardcopy The faster the CPU, the larger the memory, and faster buses the faster the data can be processed


Digitization of Analog Data :Digitization of Analog Data In nuclear medicine data is obtained in analog format Computers can’t read this format so the data must be digitized before sending to the computer for storage or processing This is done by the ADC’s and is called digitization Analog signals are continuous in time and digital signals are not as they take samples from the analog signal over time to make the digital signal The higher the bits the ADC produces, the less signal data is lost Slower ADC’s increase dead time of the system and are only good for low count rates


Digital to Analog Conversion :Digital to Analog Conversion For the data to be displayed on a monitor the data must be in the analog format and thus the digitized signal must be converted back into analog This conversion is done by the DAC’s Connected to the computer through video interface cards


Digital images :Digital images Digital images are characterized by two quantities: Matrix size Pixel depth The gamma detector is referenced as a square matrix of definite size (ranges from 32x32 to 1024x1024, 1k to 1M pixels) Each pixel corresponds to a specific location on the detector


Digital images :Digital images The x and y pulses are acquired from the PMT’s and digitized and stored in the corresponding pixel of the matrix The amount of data able to be stored in a pixel depends on the pixels depth(byte or word) A 1 byte pixel can store 2^8 events (256) or 2^16(65,536) The pixel size is an important factor that affects the spatial resolution of the image Pixel size is calculated by dividing the FOV by the number of pixels across the matrix


Digital images :Digital images D = FOV/(z x N) Zoom reduces pixel size increasing spatial resolution Pixel size should always be less than a third of the expected spatial resolution D < FWHM/3 Pixel size greater than this limit will degrade the image Pixel size much smaller than 1/3 reduces the amount of counts per pixel thus increasing the noise in the image, decreasing the signal to noise ratio and degrading image contrast


Digital Data Acquisition :Digital Data Acquisition Data from scintigraphic studies is stored in two ways: List mode Frame mode Frame mode is the most common way of storing data in static, dynamic, gated and SPECT acquisitions


Frame and List Mode :Frame and List Mode In frame mode the x and y coordinates are sent to the corresponding pixel of the data matrix and summed for the time that the frame is to be taken for In list mode each and every event is recorded one after the other (string of data) Timing markers are added and gating marks can be added to the string of data to take out arrhythmias


List Mode :List Mode List mode has the advantage that the data is more flexible and the disadvantage that it takes more memory The advantages this flexibility provides are the ability to: Measure and correct respirational displacement of the ventricle to minimize motion blurring Form gated sequences representing only a specific aberrancy for detection of ectopic ventricular foci Use the stored multispectral energy information to perform scatter correction on the dynamic images Applying a variable zoom window after the fact to keep the ventricles centered for analysis Improving temporal precision necessary to analyze complex ventricular dynamics associated with aberrant neural conduction affecting the synchrony of muscle contraction


Static Study :Static Study Collection of data in one view of a region of interest in an object for a preset time or preset total counts Matrix size is determined before the acquisition Generally 2-3mm is considered appropriate for a LFOV camera(>400mm) 256 x 256 is required for the above pixel size


Dynamic Study :Dynamic Study A series of images are collected and each image (frame) is acquired over a certain period of time selected by the operator. The matrix size and the frame rate (time of acquisition) can be changed. Data in dynamic studies can be collected in a sequence of several phases: 1 frame per second for 1 minute 1 frame /minute for 5 minutes 1frame/10 minutes for 2 hours


Dynamic Study :Dynamic Study The choice of frame rate for a given study depends on the kinetics of the radiotracer through the organ of interest. Common Matrix size: 64x64 128x128 256x256


Gated Study :Gated Study The gated study was introduced in the mid-1970s to determine the ejection fraction of the heart by acquiring two images. At end diastole At end systole Later substituted by continuous acquisition of data in multiple sequential images (MUGA) in each cardiac cycle by gating between successive cycles.


Gated Study :Gated Study In the MUGA study, the data are acquired in synchronization with the R-wave of the cardiac cycle. Normal Heart beat is about 1 beat/second, and the R-R interval is therefore about 1 second. The R-R interval is divided into several segments or frame( 16-32 segments). Count rate of a typical cardiac study is 10,000 to 20,000 counts/sec 64x64 or larger matrices


Gated Study :Gated Study


Reconstruction of Images :Reconstruction of Images In planar imaging, the acquired data are displayed in a two-dimensional images without further processing. In tomographic imaging, data are acquired in different angular projections around the patient in 3-D.


Superimposition and Subtraction of Images :Superimposition and Subtraction of Images It has been common practice to superimpose image data from on modality onto another for better interpretation of the images. CT, MRI, and Nuclear Medicine studies are used to match the functional abnormalities with the anatomical defects Subtraction of images is to take away back-ground activity from an image or one set of images from another set.


Superimposition and Subtraction of Images :Superimposition and Subtraction of Images


Display :Display Cathode Ray Tubes (CRT) or Liquid Crystal Display (LCD) These monitors are placed in a work station where the nuclear physician view, manipulate, and interpret the images using the computer. Display can be on a gray scale or color scale. Grading of scale is achieved by variation in counts in the pixels in the digital image. The number of pixels defines the brightness level of a pixel.


Display cont’d :Display cont’d Color scale blue, green, yellow, and red are assigned in the order to pixels with increasing counts: blue to the lowest count and red to the highest. Images can be displayed in transaxial (transverse), coronal (horizontal long axis), or sagittal (vertical long axis) individually or simultaneously on the monitor. Angular projections around an object computed from the 3-D tomographic data can be displayed in continuous rotation. Presents image data in a movie mode.


Display cont’d :Display cont’d Polar images, the activity distribution in an object is essentially unfolded from inside out, and three dimensional data are presented in a two-dimensional format. Major advantage of the technique is that one can identify the location of the defect in relation to adjacent areas on the single images


Software and DICOM :Software and DICOM Software is a collection of instructions for the computer to perform in carrying out a particular imaging study. American College of Radiology and the National Engineering Manufacturing Association (NEMA) sponsored a standard format for the software, called Digital Imaging and Communications in Medicine (DICOM)


Software and DICOM cont’d :Software and DICOM cont’d DICOM format: Image storage Protocols for intertransfer of data between the workstation and PACS Query and retrieval of image data Print and scheduling of data acquisition. DICOM is encoded in binary form


PACS :PACS Picture Archiving and Communication System (PACS) Used for the archiving and exchanging of patient information among health professionals. Consist of devices to produce and store digital images electronically workstations to view and interpret images, and a networking of these devices at different sites. Appropriate PACS software allows the interpreter to retrieve images form other locations and manipulate and interpret them as needed at his own location, and then return them with a report back to the original location.


PACS :PACS Radiology Information System (RIS) Is normally implemented to maintain all types of workflow, such as image reporting, all the billing codes, and so on within department. Health Information System (HIS) Maintain similar information on patients including their demographic data, laboratory data, clinical history, and medication, and again scheduling, tracking, reporting , and billing.


PACS :PACS


PACS :PACS


Summary :Summary Basic elements of a computer CPU, Memory, Input/output devices Non-imaging Applications Patient Scheduling, Record Keeping, Archiving, Inventory of Supplies, Quality Control Log, Budget Management Digitization Digital signals are a sample of time points of the analog signals Computers operate according to instructions from a program being used by an operator


Summary :Summary Analog signals are continuous in time and digital signals are not Data must be in analog format for video displays Matrix size and pixel depth are important aspects of an image Scintigraphic data can be stored in list mode or frame mode static images dynamic study gated study reconstruction of Images Superimposition and Subtraction of Images display monitors software and DICOM PACS


Works Cited: :Works Cited: http://pcwin.com/software/Mergedpm Christian, Paul E. BS,CNMT,PET Nuclear Medicine and PET/CT Saha, Gopal. Physics and Radiobiology of Nuclear Medicine. Third Ed.. NYC: Springer, 2006.


Q & A :Q & A What is the difference between RAM and ROM memory? RAM is temporary, ROM is permanent List some non-imaging applications Recordkeeping, Unit Dose Manager, Computer logbook List some Input and Output Devices and describe what each do Input- Mouse, Keyboard Output- Printer, LCD screen Would you use a faster or slower ADC for higher count rates? Faster in order to handle the high count rates


Q & A :Q & A Define PACS Picture Archiving and Communication System Used for the archiving and exchanging of patient information among health professionals Digital images are characterized by what two quantities? Matrix size Pixel depth Data from scintigraphic studies is stored in two ways: List Mode Frame Mode In a Bone Scan whole body acquisition, what is the scan speed? 10cm/ minute


Q & A :Q & A How is list mode different from frame mode in how it is saved? Frame mode- the x and y coordinates are sent to the corresponding pixel of the data matrix and summed for the time that the frame is to be taken for List mode - each and every event is recorded one after the other (string of data) Which phases of a Three phase Bone scan are in a Dynamic mode and Static mode? Dynamic- Phase 1 Flow Static- Phase 2 and 3