Index of Medical Imaging

Jonathan McConnell

• Publisher: Wiley-Blackwell
• Year: 2011
• ISBN:
  9781444340976
• Edition: 1
• Topic: Medicine
• Subtopic: Radiology, Radiotherapy & Nuclear Medicine

The 'Index of Medical Imaging' is the must-have companion for diagnostic radiography students and newly qualified imaging practitioners, designed to allow easy access to descriptions and discussions of many aspects of medical imaging such as radiographic projections, positioning, procedures and clinical examinations.

The Index consists of multiple lists, tables and discussions linked to (amongst others) radiography, CT, MRI and components such as radiological contrast agents, responses to contrast reactions, MRI safety. There is a glossary of terms and definitions plus a list of abbreviations that may be encountered within radiology. Tables are given that suggest the order and type of examination that should be performed as defined by the UK Royal College of Radiologists.

FEATURES
• Supports clinical decision-making
• Glossary of key terms and abbreviations
• Unique format that consists of multiple lists, tables and discussions

Chapter 1

Positioning Terminology

The standard anatomical position is assumed, with the individual standing facing the observer with feet turned slightly outwards and hands abducted away from the body and palms flat and visible. In respect to this, several terms can be discussed from this starting position to describe positioning and relations of structures.

Relational Terms

Anterior towards the front of the body; alternative term is ventral

Posterior towards the back of the body; alternative term is dorsal

Medial towards the midline of the body

Lateral away from the midline towards the side of the body

Proximal towards the origin of the structure

Distal away from the structure’s origin (or further from the body)

Superior towards the head (cranial or cephalad) or above

Inferior towards the feet (caudal/caudad) or below

Oblique from the anatomical position rotation of the body in either direction

Anatomical Planes

Sagittal The mid or median sagittal plane vertically divides the body into two equal (right and left) halves. Other sagittal planes are subsequently parallel with this.

Coronal A second vertical plane that can pass through the body to divide it into anterior or posterior sections lying at right angles to the mid-sagittal plane.

Transverse These are also termed axial planes; the transverse plane divides the body into superior and inferior sections so generating horizontal cross-sections.

Body Movements

Understanding body movements is important so that the correct position is adopted for images that may be produced.

Flexion bending a joint to bring the components closer to each other

Extension stretching of a joint to separate or elongate joint components relative to each other

Supination a movement that allows the anterior surface to lie upwards

Pronation a movement that allows the anterior surface to lie downwards

Adduction movement of a limb towards the midline (or closer to the body)

Abduction movement of a limb away from the midline

Inversion rotation of a joint towards the midline

Eversion rotation of a joint away from the midline

Internal rotation rotation towards the centre of the body

External rotation rotation away from the centre of the body

Decubitus to lie on a surface of the body and direct a horizontal beam X-ray toward the patient, e.g. dorsal decubitus is to lie on the back with image receptor alongside the patient and effectively a lateral projection is generated by the horizontal ray. Lateral decubitus would have the patient lying on their side.

Chapter 2

Digital Radiography Considerations

Digital radiography, it has been argued, is seen as a massive leap forward in terms of image archiving, manipulation and dose saving. There are, however, a few points that should be remembered when using these systems as the situation is not as simple as it may first appear.

Computed Radiography

In computed radiography a photo-stimulable phosphor is the image receptor. X-radiation is captured as a ‘shadow’ representation of transmission of the beam through the patient, energy amounts being dependent upon what materials the beam passes through, i.e. greater absorption through bone, least through gas-filled structures, and varying according to the thickness of soft tissues elsewhere. The captured energy is released by spraying laser light onto the phosphor; this releases light detectable by a photomultiplier system which amplifies the signal and converts it to a digital data stream. The data stream is then applied to a monitor whereby the data represents grey values on a scale. These are reconstructed in a matrix (pixels) to generate images familiar to the viewer as the radiograph.

Direct Digital Radiography

Direct digital systems do a similar job but use amorphous silicon or selenium linked to a thin film transistor that has rows and columns of switches equal to the pixel in the image. When the switch is activated the energy stored by the transistor system downloads its information, again as a data stream, though this time a conversion process is not necessary, thus making for a faster response time. These systems are built into equipment as bucky devices or connected to tables and erect stands via cabling or wireless download capabilities so that the receptor can be used in ways similar to (though heavier than) the cassette approach seen in computed radiography.

Patient Information

Patient information is applied to each image through the network system termed PACS (Picture Archiving Communication System) which communicates with the Hospital and Radiology Information System (HIS or RIS). The radiographer should ensure an anatomical marker is visible in the imaging field, as digital addition of this information afterwards is not best practice.

Exposure and Digital Radiographic Systems

Digital radiographic systems are able to correct for poor exposure factor selection (overexposure by up to 500% and underexposure by about 80%), which at first sounds advantageous. However, this has led to the phenomenon of ‘dose creep’ whereby imaging staff have gradually increased exposures to avoid image noise generated by underexposure, in the knowledge that overexposure is compensated for by the system. This, over time, has resulted in much higher average exposure factors than those seen in the old film and intensifying screens that gave instant feedback through the analogue image that demonstrated an overly light or dark image. The only way the radiographer can measure the results and relative dose received by the patient is to look at the ‘Exposure Index’ value delivered by the equipment. This number is a measurement of the energy received by the CR or DR system and corresponds to relative image density. Understand how the system you are working with represents this value, as terms such as ‘S value’ from Fuji, ‘lgM’ from Agfa and variations in the position of a decimal point may lead to confusion; e.g. Kodak gives values between 1600 and 2200 whereas Agfa will display 1.6–2.2 as indications of energy deposited in the system. It is also important to know the speed at which the image was processed. Standard processing would be 100 for extremities, but selection of a faster speed would create the same amount of image blackening for a lower radiation dose. This is advantageous but, if the signal level in the subsystem drops too far, noise is introduced. Furthermore, knowing the speed and exposures can be a useful indication of how to reduce dose while maintaining adequate image quality.

Key elements to keeping dose within acceptable limits and improving image quality include:

• Centralising of the body part to the receptor as images are read from a central point and therefore are electronically adjusted based on this.
• Keeping collimation tight and aligned with cassette edges.
• Using a single cassette per image as this allows shuttering of extraneous screen to improve viewing conditions, better reading of the image data according to selected algorithm and, depending on cassette type, better use of available pixels to enhance spatial resolution.
• Ensuring the correct reconstruction algorithm is applied to the examination. The image may be affected where more than one exposure is added to a single receptor. As a result scatter beyond the collimators causes spurious analysis of the image histogram by the computing system. Take care as each system works slightly differently.

Correct viewing of the image monitor is also crucial to ensuring that a good-quality image is sent to the radiologist’s monitor for interpretation. View all images by looking straight at the monitor and not off eye-line, as this can give the impression that all is well with the image when the image quality sent for interpretation is poor. Remember, the radiographer’s workstation does not have the same detail functions as the radiologist, so an apparently acceptable image may be grossly unacceptable when viewed elsewhere.

Chapter 3

Plain Radiography Projections

Cross-references in this chapter are to entries in the named projections section in Chapter 4. Projections are suggested singularly on digital cassettes or plates to avoid the issues discussed in Chapter 2.

LOWER LIMB EXAMINATIONS

Foot

ANTEROPOSTERIOR HALLUX (DORSIPLANTAR FIRST OR GREAT TOE)

The patient’s shoes, socks and dressings are removed to prevent artefacts. The patient can lie supine on the examination table with a pillow under the head (or sit on the examination table/trolley) with the knee flexed so the foot rests flat on an 18 × 24 cm image receptor. If immobilisation is required, use a large foam pad along the medial border of the leg or flex the other knee to support the affected side.

Use a vertical IR (incident ray) centred to the first metatarsophalangeal joint. Some authors recommend an angle of 10–15° toward the calcaneum to prevent foreshortening of the phalangeal and metatarsal long axes, and correct visualisation of the toe will occur. Ensure collimation to include the neighbouring (second) toe and expose using a 100 cm SID.

LATERAL PROJECTION OF THE TOE

This projection is usually reserved for the hallux as being the structure that bears most weight distally. The affected leg should be rotated medially, facilitated by flexing the affected knee, until the great toe is in a lateral position. To ensure that the toe can be adequately visualised, insert a small foam pad between the adjacent toes and, in the case of the great toe, wrap a small bandage around the smaller toes and extend the bandage around the posterior aspect of the heel. Ask the patient to hold the bandage so that the toes will be pulled inferiorly so that the great toe is separated from its neighbours.

Centre a vertical IR to the metatarsophalangeal joint and collimate to include the digit and metatarsal base.

DORSIPLANTAR OR ANTEROPOSTERIOR PROJECTION OF THE FOREFOOT

Similar to the AP/DP of the hallux, where the patient flexes the knee so the foot can be placed in contact with the 18 × 24 cm image receptor that is positioned transversely, so the forefoot is placed so that it rests on one half. Using a vertical IR, centre to the shaft of the third metatarsal and collimate on four sides to include the whole of the forefoot from toes to the cuneiforms and cuboid.

WEIGHT-BEARING DORSIPLANTAR PROJECTION OF THE FOREFOOT

To show the impact of metatarsus primus varus (precursor to hallux valgus) and the impact of weight on the feet.

The patient stands on the image receptor placed transversely to accomm...

Table of contents

• Cover
• Dedication
• Title page
• Copyright page
• Index Layout and Acknowledgements
• Chapter 1 Positioning Terminology
• Chapter 2 Digital Radiography Considerations
• Chapter 3 Plain Radiography Projections
• Chapter 4 Named Radiography Projections
• Chapter 5 Procedures Using Contrast Agents +/− Fluoroscopy
• Chapter 6 Mobile Radiography and Fluoroscopy
• Chapter 7 Diagnostic Angiography
• Chapter 8 Contrast Media, Emergency Drugs and Reaction Responses
• Chapter 9 Computed Tomography Protocols
• Chapter 10 Magnetic Resonance Imaging Safety
• Chapter 11 Magnetic Resonance Imaging Sequences
• Chapter 12 Typical Effective Doses from Diagnostic Medical Imaging Procedures
• Chapter 13 Indicated Imaging
• Chapter 14 Eponymous Injuries and Classification Systems
• Appendix 1 Common Radiological and Medical Abbreviations
• Appendix 2 Glossary of Common Terms for Medical Radiation Practice (including prefixes and suffixes)
• Appendix 3 Typical Normal Blood Values