308 7.8  Biomedical Physics Tools

of assisting in the diagnosis of several heart disorders from the characteristic voltage–​time

data signatures. The electroencephalogram is an equivalent technique that uses multiple sur­

face electrodes around the head to investigate disorders of the brain, most importantly for

epilepsy diagnosis.

A less commonly applied technique is electromyography. This is essentially similar to

ECG, but applied to skeletal muscle (also called “striated muscle”), which is voluntarily con­

trolled muscle, mostly attached to the bones via collagen fibers called “tendons.” Similarly

electronystagmography is a less common tool, involving electrical measurements made in

the vicinity of the nose, which is used in investigating the nerve links between the brain and

the eyes.

7.8.6  INFRARED IMAGING AND THERMAL ABLATION

IR imaging (also known as thermal imaging, or thermography) utilizes the detection of IR

electromagnetic radiation (over a wavelength range of ~9–​14 μm) using thermal imaging

camera detectors. An array of pixels composed of cooled narrow gap semiconductors are

used in the most efficient detectors. Although applied to several biomedical investigations,

the only clearly efficacious clinical application of IR imaging has been in sports medicine to

explore irregular blood flow and inflammation around the muscle tissue.

Thermal ablation is a technique using either localized tissue heating via microwave or

focused laser light absorption (the latter also called laser ablation), resulting in the removal

of that tissue. It is often used in combination with endoscopy techniques, for example, in the

removal of plaque blockages in major blood vessels used by the heart.

7.8.7  INTERNALIZED OPTICAL FIBER TECHNIQUES

Light can be propagated through waveguides in the form of narrow optical fibers. Cladded

fibers can be used in standard endoscopy, for example, imaging the inside of the gut and large

joints of the body to aid visual diagnosis as well as assisting in microsurgical procedures.

Multimode fibers stripped of any cladding material can have a diameter as small as ~250 μm,

small enough to allow them to be inserted into medical devices such as catheters and syringe

needles and large enough to permit a sufficient flux of light photons to be propagated, for

either detection or treatment.

Such thin fibers can be inserted into smaller apertures of the body (e.g., into various blood

vessels) generating an internalized light source that can convey images from the scattered

light of internal tissue features as well as allow propagating high intensity laser light for

laser microsurgery (using localized laser ablation of tissues). The light propagation is not

dependent upon external electromagnetic signals, and so optical fibers can be used in con­

junction with several other biophysical techniques mentioned previously in this chapter,

including MRI, CAT/​CT scanning, and SPECT/​PET.

7.8.8  RADIOTHERAPY METHODS

Radiation therapy (also known as radiotherapy) uses ionizing radiation to destroy malignant

cells (i.e., cells of the body that divide and thrive uncontrollably that will give rise to cancerous

tissue). The most common (but not exclusive) forms of ionizing radiation used are x-​rays.

Ionizing radiation results in damage to cellular DNA. The mechanism is thought to involve

the initial formation of free radicals (see Chapter 2) generated in water from the absorption

of the radiation, which then react with DNA to generate breaks, the most pernicious to the

cell being double-​strand breaks (DSBs), that is, localized breaks to both helical strands of

the DNA.

DSBs are formed naturally in all cells during many essential processes that involve topo­

logical changing of the DNA, for example, in DNA replication, but these are normally very