Map 5 Electromagnetic Radiation PDF

MAP.5 Electromagnetic Radiation – Use in Therapy & Diagnosis PRESENTER: Lum Chia Yuee 1 Learning outcomes Identify the main components of the electromagnetic spectrum. Restate typical values of frequency or wavelength for each of these. Describe the relationship bet...

MAP.5 Electromagnetic Radiation – Use in Therapy & Diagnosis PRESENTER: Lum Chia Yuee 1 Learning outcomes Identify the main components of the electromagnetic spectrum. Restate typical values of frequency or wavelength for each of these. Describe the relationship between energy, frequency and wavelength of photons. Recognise the role of each of the main components of the EM spectrum in relation to diagnosis or therapy of patients. Electromagnetic (EM) Radiation: Diagnosis & Therapy What is EM radiation? A complex interaction between changing Electric and Magnetic fields that is often associated with the acceleration of charged particles. An EM spectrum shows the different types of EM radiation that exist. Although the various ‘bands’ of radiation have different names, they are identical in nature, consisting of changing electric and magnetic fields. The only difference is the wavelength or frequency of the radiation. All EM radiation travels at the same speed – the speed of light (in a vacuum), c = 3 x 108 m/s. All EM radiation obeys the relationship vwave = c = f.λ (i.e. speed = frequency × wavelength) (for EM radiation, the speed of wave is often denoted by the symbol c, besides v) EM radiation consists of photons, and the photon energy (E) is directly proportional to the frequency of the wave (f), i.e. E∝f Since c = f.λ = constant, f and λ are thus inversely proportional to each other. E ∝ f implies E ∝ 1/λ or photon energy is inversely proportional to the wavelength. This is why gamma rays are more energetic than radio waves and blue light contains more energy per photon than red light. (fblue > fred or λblue < λred → Eblue > Ered) Are there any clinical implications for this?? We can see from the diagram that radiation with a frequency > ~1 x 1015 Hz will actually break bonds and cause electrons to be freed from an atom. For biological tissue, this can occur for radiation with wavelengths less than ~ 300 nm (UV) or photon energies greater than ~ 4 eV*. *E ∝ f → E = constant × f = h f = hc / λ (in Joule, J) = hc / (eλ) (in electronvolt, eV) c = speed of light in vacuum = 3 x 108 m/s h = Planck’s constant = 6.63 × 10-34 J s e = charge of an electron = 1.6 × 10-19 C E = h.f = hc/l How does the body respond to different types of electromagnetic radiation? Are there any uses for EM radiation in Medicine or Physiotherapy? 1. Short Wave Diathermy (SWD) Diathermy:- “Gentle Heating”: non-superficial heat treatment in patients. Heat:  Relieves Pain  Increases Mobilization  Improves Blood Flow (Physiological advantages of this?) SWD uses radio wave radiation in the frequency range 10-100 MHz (Typical value is 27.12 MHz) In SWD the radiation is passed to the patient via electrodes (capacitive field diathermy) or coil applicator (inductive field diathermy). The varying electrical and magnetic fields associated with the EM radiation cause the charged molecules within the tissue to vibrate, and hence the kinetic energy is converted to heat. Capacitive/ Tissues which contain a high number of free ions (i.e. Electric field muscle tissue, blood etc.) are usually good conductors diathermy & respond well to SWD. [Beware of hazards as metal and sweat also respond well to SWD] SWD can produce both superficial or deep tissue heating (the heating is a direct result of Joule Heating, E = I2Rt or P = I2R). Inductive/ Magnetic field diathermy SWD has been observed to: Increase blood flow. Help reduce inflammation. Increase the extensibility of deep collagen tissues. Decrease joint stiffness. Relieve deep muscle pain and spasm. 2. Microwave Diathermy (MWD) Water molecules (polar molecules) in tissue absorb the microwave energy. Vibrational energy converted to heat. Frequencies used are ~2450 MHz. Provides deep penetration into tissue. Caution is required as bone reflects microwave and cause burns to the tissues around the bone Precautions on diathermy SWD is contraindicated in areas with metal implants and in patients with pacemakers. Electromagnetic waves may selectively heat water; therefore, areas with excessive fluid accumulation, such as edematous tissue, moist skin, eyes, fluid-filled cavities, and a pregnant or menstruating uterus, should be avoided for both SWD and MWD. A rule of “no water and no metal” is generally recommended when using both SWD and MWD. Chueh-Hung Wu, in Braddom's Rehabilitation Care: A Clinical Handbook, 2018 Deep Heat (Diathermy) Ultrasound (eSlides 17.8, 17.9, and 17.10) 3. Infrared (IR) radiation More than half of the energy reaching the earth from the sun is in the form of infrared (IR) radiation – i.e. heat. The heat of IR radiation can be used for diathermy purpose. Near IR maybe able to penetrate up to 5mm under the skin to reach subcutaneous tissues. Therapeutic heat lamps produce a high percentage of high intensity near-IR radiation (λ ~ 1000-2000 nm). Can be used to deep-heat tissues. Increased metabolism results in a relaxation of the capillary system (vasodilation). Increased blood flow in the region of treatment. Excellent treatment for muscular and soft tissue injuries. IR radiation is invisible and can penetrate through the lens. In the case of accidental exposure to IR laser, IR radiation be focussed onto the retina without notice – could be hazardous in the form of a retinal burn. Would we feel any pain?? Is the location of the burn on the retina important?? Implications for clinically used lasers?? Another application related to IR radiation is Thermography. But what is thermography and when can we use it? All objects with a temperature greater than absolute zero emits radiation with different intensity over a spectrum of wavelength. The peak wavelength of the radiation spectrum is inversely proportional to the objects temperature. By Wien’s Law, λpeak = B / T where B is Wien’s constant (2.9 × 10-3 m K) and T is temperature in Kelvin.  Graph of intensity v.s. wavelength of radiation emitted from an object at temperature T (in K) Wien’s Law So what wavelengths do human body (at 37 oC) emit??? On the other hand, Stefan’s Law states that the power of radiation emitted by the body (W) is determined primarily by the temperature of the body, i.e. W = eAσT4 Where: e is the emissivity, A is the area of the body σ is the Stefan-Boltzmann constant (5.67 × 10-8 W m-2 K-4). Since the power of radiation is proportional to T4, if we can ‘map’ or measure the radiation power as a function of position, this gives a very good map of surface temperature. Humans emit EM radiation in the infrared region, allowing infrared cameras to accurately map the surface temperature of the body via Wien’s Law or Stefan’s Law. Such a technique is called Thermography. Since blood flow is an efficient means of heat transport within the body, Thermography can give a good indication of surface blood distribution (although there are mixed views on its clinical usefulness nowadays). It has been used as a good ‘first-indicator’ of tumours in breast cancer patients, as well as identifying areas of reduced blood flow in patients with diabetes or vascular problems. Low resolution thermographs showing normal breasts (left) and severe breasts asymmetry (right). High resolution thermographs showing severe fibromyalgia pre- (top) and post-treatment (bottom). 4. Visible radiation Eye – simply look at your patient. Fibre-optic Endoscopes. Ophthalmoscope. Otoscope. Much of the white light used in endoscopy contains http://blog.teachersource.com/2015/06/17/ ultraviolet-light-humor/ Infrared (IR) radiation (basically heat) and it is therefore desirable to use IR filters to absorb this, and minimise unwanted heating of healthy tissue (cold light endoscopy). Regions which can be Endoscopy investigated using endoscopes. Colon - Vocal cords Haematoma Colon - Polyp Trapped meat Transillumination refers to the transmission of light (usually visible) into various parts of the body for the purposes of diagnosis. A red glow is often associated with Transillumination - Why?? Red light will penetrate further into tissue and undergo scattering, while blue light is more easily absorbed at the tissue surface. Transillumination can be used effectively to detect hydrocephalus in infants. Since the skull is not fully calcified in infants, visible light penetrates quite easily. If there is an excess of CSF, light will be scattered to different parts of the skull producing a characteristic pattern. Transillumination can also be used to diagnose pneumothorax, as well as studying problems with the gums, sinus cavities and breasts. Visible Lasers – Photodynamic Therapy (PDT) A photosensitive drug is administered to the patient and after some period of time, it will be selectively taken up by cancerous cells. When the cancerous area is exposed to light of a certain wavelength, singlet oxygen is produced which is extremely toxic to the cancer cells. Once the photosensitive drug (usually a porphyrin derivative) has been taken up by the cancer cells, the extent of the lesion may be observed using fluorescence. Fluorescence image showing the clear boundaries of a skin lesion which cannot be seen with the naked eye.  Recurrent cancer of the lower lip – one day post PDT treatment (Note this tumour had been surgically removed 1 year previously) Same patient one month post PDT treatment Recurrent tumours on chest wall following mastectomy. At this time radiotherapy, ‘salvage surgery’ and chemotherapy failed to prevent reoccurrence. 3-months post PDT treatment One year post PDT treatment Note: Lasers also have many other uses in medicine and physiotherapy – see later. Most clinically useful lasers operate in the visible part of the spectrum. 5. Blue light Infants suffering from jaundice (excess bilirubin excretion from the liver) respond very well to exposure from Blue light – phototherapy. The reasons are not clearly understood, but broadband light (430nm – 490nm, centred on ~450 nm) seems to produce the best effect when the infant is exposed to the lamp source for a period of 12-24 hours.  6. UV Radiation UV light has a higher frequency than visible or red light, and therefore has greater energy per photon. While this may make it more useful, it may also make it more harmful!! UV light with λ < 300 nm is germicidal - what are the implications of this?? UV light can also convert molecular products in the skin to produce vitamin D, which can improve skin conditions such as psoriasis. UV radiation also effects melanin in the skin to cause tanning. However, excessive exposure may burn and can be avoided by sunblock etc. Thekerani Rural Hospital HRW/SODIS Reactor in Southern Malawi ( see https://youtu.be/cotBM0laSSo?si=s7r1aQNpTsIe-MU7 ) However, These wavelengths are also well absorbed by DNA cells in the skin – and prolonged exposure can lead to the formation of skin cancers such as Basal Cell Carcinoma (BCC) and Squamous Cell Carcinoma (SCC). Also, be aware of ‘scattered’ UV light.  Why can’t we see UV light?? UV light is very easily absorbed in the UV light is surface tissues and never gets through absorbed by the lens at the front of the eye. the cornea & the lens Excess absorption of UV light by the lens can result in cataracts. People who have had the lens removed because of excess cataract formation can often see into the UV part of the spectrum (since the primary absorber of UV – the lens – has been removed. 7. X-rays High energy photons that are produced due to decelerating electrons. They are able to i) penetrate soft tissues but absorbed by high density tissues – can be used to differentiate tissue types, i.e. medical imaging. More details in MAP.13 to MAP.15. ii) cause ionization – can be used to kill cells and destroy tumours, i.e. treatment of cancer. More details in IHD.22. 8. Gamma-rays High energy photons that are originated from deexcitation of nuclei. They are able to i) penetrate all tissue types – can be used for medical imaging. More details in MAP.18. ii) cause ionization – can be used to kill cells and destroy tumours, i.e. treatment of cancer. More details in IHD.22. Thank you F O R M O R E I N F O R M AT I O N P L E A S E C O N TA C T Lum Chi a Yue e EMAIL: [email protected]