Is the image diagnostic? (10 point plan)

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Course: International Covid-19 support for Radiographers and Radiological Technologists
Book: Is the image diagnostic? (10 point plan)
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Date: Friday, 19 August 2022, 7:48 AM

1. Patient Identification

Before checking the technical quality of the chest X-ray image the patient’s identity must be confirmed and the images assigned to the correct patient folder on PACS.

This would also be an appropriate time to check point 3 and ensure there is the correct annotation indication the technique used and the left/right side anatomical marker.

World Health Organization (WHO) stated in 2007 that throughout the health-care industry, the failure to correctly identify patients continues to result in wrong person procedures on patients and identity errors. These are still ongoing problems in diagnostic imaging 

The English Care Quality Commission latest report for 2018/19 identifies 796 notifications of errors from Significant Accidental or Unintended Exposure’ (SAUE). The most common type of error is still when the wrong patient receives an exposure, with 50% of all diagnostic imaging errors resulting from referrers failing to refer the right patient or operators failing to actively identify their patients. (Full report at: https://www.cqc.org.uk/sites/default/files/IRMER_annual_report_2018_2019_final.pdf )

Appendix 1 has some lessons learnt from the report

Initiatives developed like a ‘quality before speed’ mission statement to support the established ‘pause and check’ (Appendix 2) recommended by the UK Society and College of Radiographers were recommended in the report.

Professional bodies have produced guidance in the UK (Society and College of Radiographers (SCoR), Royal College of Radiologists (RCR) and Institute of Physics and Engineering in Medicine (IPEM)) in an attempt to reduce errors

https://www.sor.org/sites/default/files/document-versions/patient_identification_guidance_and_advice.pdf 

The National Patient Safety Agency(UK) have also issued guidance (Appendix 3)


2. Area of Interest included

Images can only be of diagnostic quality if all the anatomical areas are included on the mobile X-ray image. These are:

  • Superiorly the supraclavicular region defined by the superior margin of the 1st rib bilaterally. 
  • Lateral margins of the chest
  • The hemidiaphragms. Collimation should be extended if the chest request include the need to identify the position of a naso gastric tube



3. Anatomical Markers and Legends

For a mobile chest image to be diagnostic it must include anatomical annotation of the left or right aspect of the chest.

All mobile radiography is adapted technique and this needs to be annotated on the image to inform the clinician and reporting practitioner

Annotation should include:

  • Right or Left

  • Mobile

  • Patient position

      • Erect,  supine or prone
    • The FDD in cm

      • If supine the X-ray tube should be as far away from the detector as possible. Reduced FRD’s result in magnification and increased Unsharpness. This may result in the lateral margins of large patients being projected off the detector

    For mobile chest Radiographs the exposure factors and time of the examination should also be included.

    In the current situation with patients with COVID 19 anatomical markers placed on the detector at the time of imaging should be avoided because of possible cross infection. Care must therefore be taken to ensure the digital image is not ‘flipped from AP to PA depending on the patient position.

     



    4. Correct projection for a mobile chest X-ray

    If the patients condition allow better quality images will be achieved if the patient is positioned in the standard radiographic procedure, PA erect with a FRD of 180 cms or further.

    Patients with Covid-19 can be managed prone to improve oxygenation. Radiographers/radiological technologists may be required to obtain PA prone radiographs, a practice that rarely occurred previously.The patient must be positioned parallel to the detector to reduce distortion and with as little rotation as possible.

    Images should be performed on full inspiration and have symmetrical reproduction of the thorax.

    For AP erect images the arms should be bent at the elbows, the hands rested on the pelvis and arm elevated if possible to minimize scapula over the lungfields. The whole bony thorax (ribs, spine and clavicles) needs to be demonstrated. Some spine detail is visualised through the heart and mediastinum. Symmetry is checked by having the medial ends of the clavicle equidistant from the spinous process

    The commonest technique errors on mobile chest X-rays are:

    • Patient rotation around the coronal plane
    • Patient leaning backward (lordotic)
    • Poor inspiration.
      • This is always a challenge for ill patients and patients with Acute respiratory distress syndrome (ARDS) so practicing the technique with the conscious patients may help
      • the 6th anterior / 10th posterior ribs should cross the hemidiaphragm on the right side
    • Underexposure of the detector
    • Missing anatomy


    5. Correct exposure indicator

    This is probably the most complex aspect of producing diagnostic images at the optimum radiation dose (ALARA/ALARP).  There is limited visual connection between the exposure given to the patient and the image displayed on the screen used to view the image. It is therefore important for the radiographer / technologist to understand Exposure Indicators (EI) and the Deviation Index (DI). Digital systems generally display images with the optimum density and contrast regardless of the exposure factors. Underexposure can result in image noise, however, overexposed images will be displayed optimally on the display screen often at ten times the exposure. Gross over exposure will result in ‘burned out’ pixels losing anatomical detail usually in the lungs.

    Image evaluation for exposure should perhaps be conducted using EIT is the EI for a given radiograph and the target exposure. The 3-point scale for producing diagnostic images is:

    1 = Unacceptable, must be repeated

    2=Marginal

    3=Acceptable

    Images should be repeated if relevant anatomical details or ability to see lines or endotracheal tubes in the mobile chest image cannot be distinguished because of poor positioning or exposure making the image undiagnostic. It’s the responsibility of the radiographer / technologist to select a technique that provides enough exposure to reduce the amount of noise while also adhering to ALARA/ALARP standards. 

    One major advantage of digital radiography systems is the very wide exposure latitude. Images will be displayed with the optimum density and contrast when the system has been set up with the required algorithm for chest imaging in our examination. As long as the detector is not underexposed or greatly overexposed a diagnostic image will be displayed. Repeat images are rarely required because of exposure errors when anatomically programmed generators are used with the equipment

    The milliampere second (mAs), Kilovoltage (kV) and FDD should be recorded for each patient and checked prior to new mobile radiographs. This will allow evaluation of the exposure, which can then be considered for future mobile images.

    Patient dosimetry:
    The radiation exposure to the patient should be recorded on a log on the mobile equipment for future imaging and in PACS/RIS for record keeping. This can be recorded as the exposure factors and the mobile used. DR mobiles may provide a Dose Area Product reading (DAP) measured in centi-Gray centimetre squared (cGy × cm2).

    Developed concurrently by the International Electrotechnical Commission (IEC) and the American Association of Physicists in Medicine (AAPM), in cooperation with digital radiography system manufacturers, the exposure index has been implemented as an international standard. It’s known as the IEC exposure index. The IEC exposure index is unique to the receptor type being used and to the exam performed.

    This will allow audit of and between systems to further optimise exposures in diagnostic imaging



    6. Optimum definition

    The mobile chest radiograph needs to demonstrate the relevant anatomy / pathology and any tubes / lines used for the management of the patient

    The mobile chest radiograph is assessed to determine if it is a visually sharp reproduction of the anatomy with limited / no distortion of:

    • Lungs
      • Lateral margins, apex and diaphragm
      • Trachea and proximal bronchi
      • Vascular pattern in the whole lung particularly the peripheral vessels
      • Costophrenic angles
      • Retrocardiac lung
    • Heart, mediastinum and aorta
      • Borders of the heart, mediastinum and aorta
    • Bone margins and cortex/trabecular patterns

    The image is also assessed to determine if the following ae clearly demonstrated:

    EndoTracheal Tube (ETT)

    The position of tip of the ETT should be 5 cm above the carina in the neutral position of neck. When the carina is not visible, the tip of the ET tube should lie between the level of the medial clavicles and aortic arch. The location can vary approximately 2 cm in the caudal or cephalic directions with neck flexion and extension, respectively on chest radiograph emphasising the need to obtain with the head in neural wherever possible. Projection of anterior portion of the mandible over the lower cervical spine indicates neck flexion whereas a non-obscured cervical spine denotes that the neck is in extension

    Central venous line

    (https://www.radiologymasterclass.co.uk/tutorials/chest/chest_tubes/chest_xray_central_line_anatomy

    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4173625/ )

    Central venous catheters are inserted through major veins such as the subclavian vein to reach the superior vena cava (SVC). The tip of the line should be distal to last venous valve, which is located at the junction of internal jugular and subclavian veins. The preferred position of the catheter tip is in the distal third of the SVC. On the mobile chest radiograph, the first anterior intercostal space corresponds to the approximate site of the junction of the brachiocephalic veins to form the SVC and the cavoatrial junction corresponds to the lower border of bronchus intermedius. The position of valve corresponds to the inner aspect of the first rib. There are also Extracorporeal Membrane Oxygenation (ECMO) catheters which have different positions depending on the method being used which should be visible.

    Nasogastric tubes

    This is available within e-LfH https://portal.e-lfh.org.uk/Component/Details/482783 

    Chest radiographs are rarely first line test for determining position of a naso-gastric tube. Gasrtic aspirate should be obtained, with a pH <5 confirming location within the stomach and that it is safe for use. NGT aspirate with an equivocal aspiration should have NGT tip position confirmed by chest radiograph.

    A correctly positioned nasogastric tube passes vertically in the midline, or just to the left of the midline, bisects the carina and passes 10 cm beyond the gastro-oesophageal junction.

    Chest drains/ intercostal drainage tubes (ICD)

    (https://www.radiologymasterclass.co.uk/tutorials/chest/chest_tubes/chest_xray_chest_drain)

    Chest drains are usually inserted through the chest wall in the mid-axillary line to reduce a pneumothorax. They are also used to drain a pleural effusion. The ICD tube has a terminal hole as well as side holes. These side holes can be identified on Chest radiograph by the interruption in the radiopaque outline of the tube. No side holes should lie outside the thoracic cavity and the integrity of the images portion of the tube should be examined (e.g. kinked)  and the tube should not float above the effusion.

    Note: Lines and tubes which are incorrectly placed may result in complications which may be life threatening and should be treated as ‘red flag’ and the clinical team notified immediately


    7. Collimation to the area of interest

    For the portable chest X-ray the X-ray beam should always be collimated to the area of interest:

    • Superiorly the supraclavicular region defined by the superior margin of the 1st rib bilaterally
    • Lateral margins of the chest
    • The hemidiaphragms. Collimation should be extended if the chest request include the need to identify the position of a naso gastric tube

    Beam limitation is an important part of the process of optimisation for the radiographer/technologist undertaking the X-ray examination. Care should always be taken not to collimate the beam too much so that relevant anatomy has been excluded. This would make the image non diagnostic  and require a repeat to be performed.


    8. Are there any artefacts and are they obscuring the image?

    Artefacts may be from a number of sources and the radiographer/technologist should be prepared to discuss any artefacts on the radiograph.

    • Patient and equipment
      • Dense collections of hair
      • Clothing, buttons / zips
      • Metal objects in pockets or around the neck and piercings
      • Skin folds
      • Oxygen reservoir, mask and tubing
      • Operative metalwork
      • Teeth knocked out by intubation
    • Detectors and Image processing
      • Noise from under exposure
      • ‘Burn out’ from overexposure
      • Detector the wrong way round.  (The tube side of the detector is clearly marked and must be facing the X-ray tube)
      • Grid lines from radiographic grids

    ECG lines and any equipment should be moved to the edges of the patient so as not to obscure the lungs.


    9. Any repeat radiographs or further projections

    The image should be evaluated using all of the previous 8 points and if the image meets the criteria it should be made available to the referrer and stored on PACS. Mobile chest radiographs which do not answer the clinical question must be repeated. If there is any doubt the decision should be made by liaison between the radiographer/ technologist  who has performed the X-ray and the referrer and the outcome recorded on PACS.

    If the image produced is diagnostic but poor quality the image does not need repeating but lesson can be learnt for following examinations.

    Audit and multi-disciplinary meeting are a useful way of recognising poor techniques or trends which can be feedback to the radiographers/ technologists to improve their imaging technique.


    10. Anatomical variations & pathological appearances

    Anatomical variations

    There are a number of anatomical variants on mobile chest radiographs. The radiographer/ technologist must be aware of common variants and their imaging appearances. This is available at:

    https://portal.e-lfh.org.uk/Catalogue/Index?HierarchyId=0_33_30128_374&programmeId=33 

    These include:

    • Dextrocardia with or without situs inversus.
      • This can be accidentally displayed by the radiographer/technologist when processing the image. The computer protocol will automatically display the image depending on the examination selected, AP or PA. Images are displayed in the anatomical position and can be flipped
    • Azygous fissure. This can be seen on the right side in a small number of chest X-ray images (1-2%). The azygos vein lined with visceral and parietal pleura makes a small connection with the rest of the upper lobe.
      • Accessory fissures can also be seen occasionally on chest images
    • Cervical rib and rib variants.
      • Cervical ribs are usually bilateral (80%) but are rarely symmetrical. They arise from the seventh cervical vertebrae and are usually asymptomatic.
    • Calcification of the cartilages.  Costochondral calcification of the anterior and/ or medial ends of the ribs is more prominent with ageing and can be particularly marked in some individuals
    • Scoliosis makes image interpretation more difficult and is accompanied with rotation of the thorax. Assessment of heart size may not be accurate
    Pathological appearances

    Chest radiographs are one of the front line investigations for Covid-19. Characteristic findings are bilateral, peripheral ground glass opacities and consolidation. Pleural effusions and lymphadenopathy are uncommon. Chest radiograph sensitivity has been reported to be around 70% when compared to reverse transcription polymerase chain reaction (RT-PCR). However, in a single series, chest radiographs were abnormal in 9% of cases with a negative initial swab. It is important that decision on healthcare PPE and cohorting of patients integrate clinical risk as well as imaging findings.

    It is important for radiographers to recognise other non-Covid-19 pathology that could explain the patient’s symptoms including pneumothorax, pleural effusion and pulmonary oedema.

    The following links have recent peer reviewed articles on  COVID 19 and the appearance / value of chest radiographs:

    Case report: A case series to support radiographer preliminary clinical evaluation by Woznitza N., Nair A. and Hare S.S.

    https://www.radiographyonline.com/article/S1078-8174(20)30054-7/pdf

    Frequency and Distribution of Chest Radiographic Findings in COVID-19 Positive Patients by Wong et al

    https://pubs.rsna.org/doi/10.1148/radiol.2020201160

    *UPDATED**Version 2 BSTI COVID-19 Guidance for the Reporting Radiologist and data base

    https://www.bsti.org.uk/standards-clinical-guidelines/clinical-guidelines/bsti-covid-19-guidance-for-the-reporting-radiologist/

    BSTI reporting templates/standards can be found at:

    https://www.bsti.org.uk/covid-19-resources/covid-19-bsti-reporting-templates/

    Appendix 4 has 4 diagnostic quality images which can be classed as: Bilateral asymmetrical mid-lower zone ground opacification. Classical/Probable COVID.