Optimisation Strategies Ali B alhailiy

What is Meant by Optimisation ♥Optimisation in digital imaging means appropriate strategies/procedures are in place in the imaging practice to ♥maximise factors that improve production efficiency and quality and to minimise factors that cause patient detriment ♥use technical measures so that images of diagnostic quality are obtained at a patient dose as low as reasonably achievable, economic and social factors being taken into account (ALARA, ICRP 103). ♥Optimisation involves team work, an input from radiologists, medical physicists, radiographers, PACS managers, application specialists and service engineers; training is essential.

Digital Imaging Process In digital imaging ♥image acquisition ♥image processing ♥image transmission ♥image display ♥image storage are separated, each can be optimized separately

CR/DR OPTIMISATION STRATEGIES

Step 1 - Step 1 - The justification of a practice The decision to adopt or continue any human activity involves a review of benefits and disadvantages of the possible options, e.g., choosing between the use of X Rays or ultrasound Most of the assessments needed for the justification of a practice are made on the basis of experience, professional judgement, and common sense

Step 2 – Specialised Training ♥The most important step is specialised training of radiographers particularly in dose and image quality issues with digital receptors

Step 3- Exposure factors and image appearance kV and mA do not have the same affect on the image quality as in film screen kV kV: While kV controls the penetrating power and therefore subject contrast, changes in kV have less of a direct effect on final image contrast as the image processing and adjustment of display window width controls the majority of the contrast seen. Higher kVp values reduce entrance skin exposure (ESE)

Exposure factors and image appearance (Cont’d) mAs mAs: mAs controls the number of x-rays forming the image and therefore image noise; digital processing (brightness control/noise reduction algorithms) allows for correction of inaccurate mAs selection.

Step 4: Understanding Exposure Index or DDI Exposure index or DDI is manufacturer specific. ♥It reflects the radiation exposure incident on the image receptor, and how much amplification was needed to produce the image.

Step 5 - Correct Positioning ♥Positioning errors have been identified in several studies as the number one reason for having to repeat digital radiography examinations. ♥Correct positioning is also vital for exposure data recognition in CR and DR ♥In case of CR when laser scans it is looking for area of the plate that has exposure ♥Works best when image is centred.

Step 6 - Collimation ♥Convenience of taking digital images leads to covering a larger area of a patient's body and using digital cropping (post processing) ♥Poor collimation ♥Large part of the body is irradiated ♥Not seen on digitally cropped image IAEA L04: Radiation Protection in digital radiography

Collimation (Cont’d) ♥Good collimation reduces scatter and improves image quality (same as in screen film) ♥It reduces unnecessary dose to the patient ♥During the exposure data recognition stage, the region of exposure i.e. collimation edges are detected; with bad collimation extraneous data is included in the histogram, this can skew the image analysis (more greys and less detail)

Step 7 Correct Selection of Chambers ♥When using AEC, ensure that the anatomy of interest covers the correct AEC chamber(s) and the system selects correct chamber. ♥In two different surveys of chest radiography it was noted that incorrect selection of chamber increased patient dose by ~ 3 to 4 times for chest PA scan.

Step 8 Correct Technique Charts ♥During x-ray exams critically review the acquired images, image processing and display conditions. New digital systems/optimisation may require different tube potentials and filtration. When technique factors are stabilised, display appropriate technique chart near the console for manual exposures ♥AEC helps control total mAs, but the radiographer still is responsible for selecting optimum mA (if set) and kVp for an examination when using AEC, and technique charts help ensure consistent use of these factors.

Step 9 - Added filtration ♥Be aware that added filtration can decrease dose to patient without compromising image quality, provided tube output is high enough; ♥In a research study at Westmead hospital, it was found that additional filtration of 0.1 mm copper + 1 mm Al in chest radiography reduced patient entrance surface dose by ~ 35%. No significant difference was found in perceived image quality of chest images with reduced dose technique including additional filtration of 0.1 mm copper + 1 mm Al. Therefore, the use of added filtration is to be encouraged. Austras Phys Eng Sci Med 2012 Mar 35(1): 71-80

Steps to have an optimum Radiological exam

Establish a QA Program Quality assurance is a management tool that includes policies and procedures designed to optimize and continuously improve the performance of personnel and quality of a product or service Quality assurance program in an imaging practice may include ♥ Administrative procedures for continuous improvement in patient care/patient scheduling/timeliness of reports ♥ Department policies to manage radiation protection issues ♥ Equipment quality control and optimization for technical effectiveness, efficiency and compliance ♥ In-service education for continuous improvement in staff performance ♥ Auditing – analyzing records of operation and reviewing the QA program

Benefits of a QA Program Diagnostic imaging is a multi-step process. There are various sources of variability in both human factors and equipment factors that can produce sub-quality images/incorrect diagnosis/increased patient dose if not properly controlled. Quality assurance program can result in ♥ Improved image quality ♥ Patient and staff care by optimizing dose and therefore reducing risk associated with radiation ♥ Reduced re-take ♥ Increased patient satisfaction/professionalism

The technologist verifies: – the patient is the person identified in the exam request – the anatomy to be examined matches the exam request – other information about the patient, such as Pregnancy Restricted motion Allergies Appliances QC accomplished by training or checklist Step1- patient report for an examination

Step 2 – radiographer identifies the patient and exam to imaging system Usually occurs before, but sometimes after the exam is performed Misidentification has consequences – incorrect information can cause image unavailability – incorrect exam info can affect image development – mis-association complicates error detection – proliferation of digital images complicates correction

The best image,improperly identified, is useless Wrong patent name.ID

Step3- radiographer positions the patient and performs the exam Potential errors – mispositioning – patient motion – incorrect radiographic technique selection – poor inspiration – improper collimation – incorrect alignment of x-ray beam and grid – wrong exam performed – double exposure QC accomplished at acquisition station? – Image processing inadequate to correct – Correction requires repeated exam (s) 80

Step 4:Image receptor captures the radiographic projection Potential errors – Inadequate erasure, lag, ghosting – Improper compensation for non-uniform gain – Incorrect gain adjustment – Incorrect exposure factor selection – artefacts Interference with the projected beam Receptor defects Interference with converting the captured projection into a digital image

Step5- image receptor renders the captured projection for viewing Potential errors – Incorrect Exposure Field recognition; incorrect determination of values of interest (VOI) – Incorrect histogram re-scaling – Incorrect gray-scale rendition – Incorrect edge restoration – Inappropriate noise reduction – Incorrect reorientation QC possible at acquisition station? – Correction usually possible without repeated exam

Potential errors – Transmission failure – Image deletion – Information omitted from transmitted image Exposure indicator Processing parameters Shutters Annotations

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