Fauber Chapter 5

DIGITAL IMAGE PROCESSINGThe shape of the histogram re

• Various computer algorithms (mathematical computations) applied to digital data for the purpose of optimizing the image for display.
• Digital image processing can be described in stages, pre-processing to prepare the data for processing and display, and default (preset) or post-processing which include computer operations available before and after the image is displayed. 

PRE-PROCESSING

• Several operations occur on the raw image data to prepare for further processing in order to display a quality image. 
• Software corrections can be applied to account for imperfections (bad or dead pixels) which only occur with DR type IRs and flat fielding is a process of correcting the nonuniformity of pixel values throughout the entire image. 
• Histograms are graphic representation of a data set of the image. This data set includes all the pixel values that represent the latent image after the software corrections were applied and sometimes referred to as the exposure histogram.
  • The x-axis represents the range of pixel values assigned. The Y-axis represents the number of pixels for each value. The location of the graph along the x-axis represents the frequency of pixels for each value. 
  • The location of the graph along the x-axis represents image brightness levels, and the shape of the graph represents image contrast.
  • The computer software has stored histogram models, each having a shape characteristic of the selected anatomic region and projection.
  • In CR imaging, the entire imaging plate is scanned to extract the image from the photostimulable phosphor.
    • Image processing technique to identify the edges of the image and compare to a stored preestablished histogram specific to the anatomic part imaged. If at least three edges are not identified, a histogram analysis error could occur.
  • Values of interest (VOI): the range of histogram data set that should be included in the displayed image.
    • The average value of the VOI is determined and used to provide important information to the radiographer regarding the exposure to the digital IR. The exposure indicator provides a numeric value indicating the level of radiation exposure to the digital IR.

DEVIATION INDEX

• The deviation index (DI) is a value that reflects the difference between the desired or target exposure to the image receptor (IR) and the actual exposure to the IR.     
  • DI Value     Actual Exposure to IR     
  • >+3.0     Excessive exposure     
  • >+1.0     Overexposed     
  • <+0.5     Exposure within target range     
  • 0            No difference between target (desired) and actual exposure to IR 
  • >−0.5     Exposure within target range     
  • <−1.0     Underexposed     
  • <−3.0     Insufficient exposure     

LOOKUP TABLES

• A method of altering the image to change the display of the digital image
• Original pixel values can be altered to change the display of the digital image.
• Alters the brightness and gray scale of the digital image using computer algorithms.
• If the original image is altered, the original pixel values would be different in the processed image, and the graph would no longer be a straight line. 
• The pixel intensities would be calculated to display an image with a different contrast level.
• HISTOGRAM ANALYSIS
• Maintains consistent image brightness despite overexposure or underexposure to the image receptor.
• Automatic rescaling: a process of mapping the gray scale to the VOI to present a specific display of brightness.

IMAGE DISPLAY

• Soft copy viewing of the digital image occurs at a computer workstation with specialized postprocessing software.
• The quality of the digital image is also affected by important features ofExposure indicators. the display monitor, such as its luminance, resolution, and viewing conditions such as ambient lighting and monitor 
• Primary display monitors used for diagnostic interpretation must be of high quality.
• High-resolution 5-megapixel (2048 × 2560 pixels) display monitor used for diagnostic interpretation (primary).  
• Display monitor having diagonal dimensions of 54 cm (21 inches) is adequate for viewing images sized 35 × 43 cm (14 × 17 inch). 
•  Pixel pitch of 0.200 mm at a standard viewing distance of about 60 cm (24 inches).

DISPLAY MONITOR LUMINANCE

• Luminance is a measurement of the light intensity (brightness) emitted from the surface of the monitor and is expressed in units of candela per square meter (cd/m2). 
• Primary display monitors should exhibit a minimum luminance of 1.0 cd/m2, and a maximum luminance of 350 cd/m2. 
• A ratio of the maximum to minimum luminance, luminance ratio (LR), is recommended to be greater than 250 and a display monitor with a LR of 350 has improved image contrast.

POST-PROCESSING 

• Electronic masking is altering the regions viewed on the displayed image.
• Electronic masking is also known as shuttering.
• Tt is not within the standards of practice for radiographers to make decisions about removing information within the radiation-exposed field. 
• Window level: sets the midpoint of the range of brightness visible in the image.
• Window width: varies the range of shades of gray visible in the image.
• Wide window width lowers contrast
• Narrow window width increases contrast

DIGITAL MANGAGEMENT

• A complex system wide effort to ensure that people, equipment, and processes are in place to expand healthcare communication and improve patient outcomes. 
• Modern radiology practice requires efficient and effective methods for acquisition, storage, retrieval, transmission, and display of digital image data from multiple imaging modalities and throughout healthcare systems. 
• Digital communication needs in radiology also include the processing and delivery of patient data and subsequent interpretation of radiological procedures. 

IMAGING INFORMATICS

• Involves data management for radiology services both within and outside the healthcare system. 
• Managing electronic health information along with digital images (acquisition, storage, retrieval, and transmission) and their interpretation and consultation, is essential to providing effective and efficient healthcare to improve patient outcomes. 
• The safety and security of protected health information must be ensured and adhere to local, state, and federal guidelines. 
• HIPAA established national standards to protect the privacy and confidentiality of patients’ protected health information (PHI)
• A complex system wide effort to ensure that people, equipment, and processes are in place to expand healthcare communication and improve patient outcomes. 
• Modern radiology practice requires efficient and effective methods for acquisition, storage, retrieval, transmission, and display of digital image data from multiple imaging modalities and throughout healthcare systems. 
• Digital communication needs in radiology also include the processing and delivery of patient data and subsequent interpretation of radiological procedures. 
• Involves data management for radiology services both within and outside the healthcare system. 
• Managing electronic health information along with digital images (acquisition, storage, retrieval, and transmission) and their interpretation and consultation, is essential to providing effective and efficient healthcare to improve patient outcomes. 

DIGITAL COMMUNICATION NETWORKS

• Picture archival and communication system (PACS) is a computer system designed for digital imaging which can receive, store, distribute, and display digital images.
• Digital imaging and communication in medicine (DICOM) is a communication standard between PACS and imaging modalities.
• Hospital information system (HIS) and radiology information system (RIS) are computer systems for medical information.
• Health level seven standard (HL7) is a communication standard for medical information.

DICOM STANDARDS

• Header on digital images (DICOM header):
• accession number, patient name and identification number, date and time of examination, radiographic procedure, and total number of images in the study
• exposure related information such as kVp, mAs, exposure indicator, and any post or re-processing of the digital data
• Modality worklist that assists the radiographer in maintaining the accuracy of the information. 
• Grayscale Standard Display Function (GSDF) for consistent display characteristics such as, grayscale appearance and image quality.

TRANSMISSION, STORAGE, AND ARCHIVES

• Image compression:
  • Reversible compression means that there is no loss of image data (lossless) at the end user.  
  • Irreversible compression means that there is some loss of image data (lossy) at the end user and may be used to decrease transmission time and or storage space.  
• HIPAA requirement to store images and data for years. 
• Disaster recovery processes

TELERADIOLOGY

• The practice of diagnostic image interpretation outside the facility (off-site) from where the imaging data is acquired. 
• used for preliminary diagnosis for referring and emergency room physicians, after-hour interpretations and consultations, subspecialty expertise, solve manpower issues such as vacations and rural facilities having limited access to radiologists.
• Communication needs between teleradiologists and the imaging professionals include providing timely and relevant patient information, ability to answer questions regarding the procedure, and maintaining standard quality control practices.  
• The practice of teleradiology should maintain the same high standards, safety, and quality as on-site radiology services.

QUALITY CONTROL, SECURITY, AND PHI

• Quality control (QC) is an important activity to ensure that radiographic equipment is functioning properly and should occur routinely and consistently.  QC activities are equally important for digital image data management and most likely performed by an imaging informatics professional.  
• Policies and procedures must be in place and adhered to by all healthcare workers who have access to PHI. 
• anonymization (patient identifiable information is removed from the PHI) if performing clinical research, 
• authentication to verify the identity of the user of PHI, 
• authorization which limits access to PHI for approved users only, maintaining records of interactions with PHI (auditing), and 
• confidentiality to prevent unauthorized users from access to PHI. 
• Radiographers have routine access to PHI in performance of their duties and must take responsibility for adhering to the department’s policies and procedures. Patients must be confident that radiographers have the skills to perform their imaging procedures and believe that their PHI will be secure.