1.3 Medical imaging

Overview of Medical Imaging

  • Medical imaging, also known as radiology, is a critical field that uses various techniques and technologies to visualize the internal structures of the body, facilitating diagnosis, treatment planning, and monitoring of diseases.

Types of Medical Imaging:

  • X-ray:

    • Uses Ionising radiation to create images of the body's internal structures, making it particularly useful for identifying fractures, infections, and tumors.

    • Absorption of x-rays varies dependent on the density of the tissue

    • Good for dense structures like bones or structures of different density that are adjacent to each other, such as the lungs where air is soft tissue and bone.

    • Cheap and accessible

    • Risk of xrays

      • Risk of radiation

      • Risk is higher in pregnancy and paediatric patients

    • Advantages:

      • Relatively cheap

      • Quick, accessible and can be mobile

    • Disadvantages

      • Produced a static image that has limited details

  • CT (Computed Tomography):

    • Uses ionising radiation

    • Produces multiple slices which can be reconstructed into a cross-sectional image

    • Can be performed with IV contrast to provide greater detail and highlight vessels and the vascularity of structures

    • Advantages:

      • Relatively accessible

      • Relatively quick for the actual scan to be done

      • Provides details for all structures within the field of view

    • Disadvantages:

      • Radiation dose is higher than X-ray

      • Patient needs to be able to lie still on the CT table while it is scanning

      • Limited use for dynamic imaging

  • MRI (Magnetic Resonance Imaging):

    • Uses Magnetic fields and radio-frequency pulses to create a static image

    • Summary of how MRI works

      1. When the body is placed into a strong magnetic field, all the protons align with the magnetic field.

      2. Radio waves are then transmitted to briefly disrupt the alignment of the protons.

      3. The protons then return to be aligned with the magnetic field but the rate at which they realign is different for each body tissue.

      4. This information is then used to generate the picture.

    • Excellent for brain and spine, muscle/tendon/ligament and joint assessment

    • MR Angiography can be performed in some instances without the use of IV contrast to provide information on vascular structures

    • Risk:

      • Metal

      • Risk in pregnancy

      • IV Contrast

    • Advantages:

      • Considered gold standard imaging assessment for a number of conditions

      • Doesn’t use ionising radiation

    • Disadvantages:

      • Claustrophobia

      • Limited accessibility

        • Time

        • Cost to operate machine

        • Size of machines

  • Ultrasound:

    • Uses sound waves to create a picture, creating a 2D image

    • Useful for assessing soft tissue structures such as the liver, kidney, muscles and tendons

    • Provides a dynamic assessment not just a static image

    • Risk:

      • Ultrasound is very safe and can be used for assessment of feta structures and on paediatric patients as ionising radiation is not being used

    • Advantages:

      • Accessible

      • Safe

      • usually cheaper than CT and MRI

      • Provides a Dynamic assessment not just a static picture

    • Disadvantages:

      • Limitations in the use of sound waves, both in terms of how substances transmit sound waves and the depth the sound waves will reach

  • Nuclear Medicine:

    • Uses Radioactive isotopes to assess function, diagnose and treat diseases

    • Common diagnostic uses include:

      • V/Q scans for pulmonary emboli

      • PET scans for cancer

      • Renal function scans

      • Thyroid scans

      • Lymphoscintigraphy

    • Risk

      • The risk varies according to the type of scan performed

      • The use of radioactive isotopes for nuclear medicine studies means that the risk of ionising radiation is an inherent part of it

  • Each imaging technique has its own set of advantages, limitations, and indications, allowing healthcare providers to select the most appropriate modality based on the clinical scenario. Furthermore, advancements in imaging technology continue to enhance the quality, safety, and accessibility of medical imaging.