Piezoelectricity

Piezoelectricity is the charge which accumulates in certain solid materials (notably crystals, certain ceramics, and biological matter such as bone,DNA and various proteins)^[1] in response to applied mechanical strain. The word piezoelectricity means electricity resulting from pressure. It is derived from the Greek piezo or piezein (πιέζειν), which means to squeeze or press, and electric or electron (ήλεκτρον), which stands for amber – an ancient source of electric charge.^[2] Piezoelectricity is the direct result of the piezoelectric effect.

Cavitation

biological bubbles - collapsing of tissue producing intense shockwaves
Intensity of hundreds of watts/cm2
Does not occur in Ultrasound

Array Transducers

Produce a scanning ultrasound beam without moving the transducer.
Real Time Image of internal structures
10 to 50 transducers mounted on a common head. Pulse:

• All pulse simultaneously 
• Pulse in sequence

Phased array allows rapid scanning of the human anatomy without moving the transducer on the skin surface

Resolution is worse than single transducers.

Doppler Ultrasound

NUCLEAR DECAY

ISOTOPES

Isotopes elements that have th same number of protons (same Z) but different atomic weights (A). The stability o an isotope depends on the relative number of neutrons and protons in the nucleus.
1.2 is the most stable ratio
1.5 the ratio rises for heavy elements
Isotopes whose ratios deviate are unstable,spontaneous decay equals radioactive.
Isotopes with even numbers of protons and even neutrons are the most stable and isotopes with an odd number of protons and odd number of neutrons are least stable.All isotopes heavier than 209 Bi are unstable.NUCLEAR FORCES HOLD THE NUCLEUS TOGETHER.
 Most nuclei have a binding energy of about 8 MeV per nucleon (i.e Carbon 12 has a binding energy of about 8x12 = 96MeV)

TYPES OF DECAY

ALPHA DECAY
BETA DECAY
GAMMA DECAY
ISOMERIC TRANSITIONS
INTERNAL TRANSITIONS
POSITRON DECAY
ELECTRON DECAY

ALPHA DECAY

During alpha particle decay a alpha particle (NUCLEUS OF HELIUM)  is emitted.An alpha particle has an atomic number of 2 and an atomic weight of 4. The decay of 226 Ra is an example of alpha decay. Alpha decay occurs when the parent nucleus has to many positive charges.

                                                                                       Z decreases by 2
                       ALPHA DECAY                                     A decreases by 4

  

X  RAY TUBES

 The anode and cathode assemblies are contained in an evacuated glass tube.

The vacuum is necessary to allow the electrons free travel from the negative  cathode to the positive anode without absorption of scattering and to withstand the high voltage applied between the cathode an anode.

Electrons are boiled off a heated filament in the cathode and accelerated to the anode. When they strike the anode of them produce x-rays.

GRID CONTROLLED TUBES

Some tubes ,focusing cathode cup is insulated from the rest of the cathode.A negative voltage can be applied to this cup to prevent any electrons from leaving the cathode while the voltage is present. Voltage cup is called the GRID voltage and can either turn the tube current on or off in a short time.The advantage of grid controlled tubes is their ability to form the short x-ray pulses needed in angiography and cineradiography.

ANODE DESIGN

Some mammographic and portable units have stationary anodes but most x-ray employ rotating anode tubes.The line focus principle and the heel effect are the same for both stationary and rotating anodes.

β− decay

β− decay in an atomic nucleus. The intermediate emission of a virtual W−boson is omitted.

The Feynman diagram forβ− decay of a neutron into a proton, electron, andelectron antineutrino via an intermediate W− boson

Radioactive decay Nuclear Decay

Alpha decay is a type of radioactive decay in which anatomic nucleus emits an alpha particle, and thereby transforms (or 'decays') into an atom with a mass number 4 less and atomic number 2 less. For example:

23892U

→

23490Th

+

42He2+ [1]

Or:

23892U

→

23490Th

+

42He

as some believe electrons are gained from the environment. 

Radioactive decay Nuclear Decay

Alpha decay is a type of radioactive decay in which anatomic nucleus emits an alpha particle, and thereby transforms (or 'decays') into an atom with a mass number 4 less and atomic number 2 less. For example:

23892U

→

23490Th

+

42He2+ [1]

Or:

23892U

→

23490Th

+

42He

as some believe electrons are gained from the environment. 

Mammography

1.1.14 Mammography
• basic principles of soft tissue and breast imaging
• types of mammography x-ray units
• emission spectra with different anode and filter materials eg molybdenum
tube and filter
• geometric unsharpness as a limiting factor
• recording system: film screen, digital
• magnification techniques
• alternative breast imaging: radionuclide imaging , US, MR
• principles and applications of stereotaxis

Xeroradiography is a type of x-ray in which a picture of the body is recorded on paper rather than on film. In this technique, a plate of selenium, which rests on a thin layer of aluminium oxide, is charged uniformly by passing it in front of a 'scorotron'.

As X-ray photon impinges on this amorphous coat of selenium, charges diffuse out, in proportion to energy content of the X-ray. This occurs as a result of photoconduction. The resulting imprint, in the form of charge distribution on the plate, attracts toner particles, which is then transferred to reusable paper plates. In contrast to conventional X-rays, photographic developers are not needed. Hence the term xeroradiography; 'xero' meaning dry in Greek. It requires more radiation exposure. Its use is in mammography.

Xeromammography is a form of xeroradiography

Spatial Resolution

Spacial resolution is effected by the following:

1. Increases Spatial Resolution
1. Increase matrix size
2. Decrease Spatial resolution
1. Increase scan diameter
2. Increase pixel size
3. No effect on spatial resolution
1. Reduce scan time
2. Increase slice thickness
3. Increase patient thickness

quantum mottle

mottle caused by the statistical fluctuation of the number of photons absorbed by the intensifying screens to form the light image on the film; faster screens produce more quantum mottle.

Any critique of radio graphic image quality must include an evaluation of quantum mottle, a fundamental limitation of the imaging process. 


Effect on Quantum Mottle:

1. Increases Quantum mottle / mottel:
1. Decrease scan time, 
2. Increase Matrix size
3. Increase Patient Thickness
2. Decrease Quantum Mottle / mottel
1. Increase pixel size
2. Increase slice thickness
3. Increase MA
3. No effect on Mottel / Mottle
1. Changing technique from 50 MA in 2sec to 100MA in 1s

Radiographic image quality characterizes the ability of an imaging system to accurately depict structures in a radiographed object. Six components affect image quality -- spatial resolution (or sharpness), contrast, density, radiographic mottle (or noise), distortion and artifacts. Of these six parameters, radiographic mottle is the most difficult to understand and relate to the imaging process. Radiographic mottle creates a grainy, blotchy, textured or snowy appearance in a radiographic image.

The final image on film is a composite of these sampling events. Increased photon absorption by the screen (a higher number of information carriers in the imaging chain) reduces quantum mottle and improves visualization of the structure.

 The component in the imaging chain with the lowest number of information carriers establishes the level of quantum mottle in the final image. This component is called the quantum sink.

Because the recording step limits the information content of the final image, this step becomes the quantum sink. The quantum sink denotes the operation in which quantum mottle has the major influence upon image resolution. The initial process of detection establishes the maximum information content that cannot be enhanced by -- and often is not preserved by -- other components in the imaging chain.

Goitre

Goitre is a non-specific enlargement of the thyroid gland, making it easily palpable and often visible. There are numerous causes but worldwide, the most common is a dietary deficiency of iodine. A very large goitre may cause compression of lower cervical and superior mediastinal structures including the trachea, making breathing difficult. CT scanning can confirm the diagnosis and define the extent of any retrosternal extension. Non-surgical options include tracheal stenting where there is breathing difficulty and the patient is not suitable for surgery. Calcified nodules within a goitre can be seen on X-ray

Glaucoma

Glaucoma involves increased intraocular pressure, which damages the optic nerve and causes partial visual loss and is the third most common cause of blindness in the West. It is characterised by increased pressure within the eyeball when aqueous humour does not drain properly, reducing the blood supply to the optic nerve, firstly affecting peripheral then central vision. Open angle (chronic) glaucoma is by far the most common type: fluid outlet channels within the wall of the eye gradually narrow over a period of years bilaterally, with consistently elevated pressure slowly damaging the optic nerve. The associated loss of peripheral vision occurs so gradually that it may go unnoticed until a substantial amount of damage and visual loss has occurred. Routine eye examination is the only way for early diagnosis. Closed angle (acute) glaucoma occurs in those with a congenitally narrow angle between the iris and the cornea – the iris may slip forward and suddenly close off the exit of aqueous humour, and a sudden increase in pressure within the eye follows – symptoms of pain, redness, nausea, and vision loss develop rapidly. Secondary glaucoma is caused by eye diseases such as uveitis, systemic diseases, and drugs such as corticosteroids.

Gag reflex

Gag reflex. Stimulation of the posterior third of the tongue or posterior oropharynx sends afferent stimuli via the glossopharyngeal (ninth cranial) nerve. The efferent pathway involves the vagus (tenth cranial) and accessory (eleventh cranial) nerves, causing elevation of the soft palate and contraction of the pharyngeal muscles. Putting a spatula against the back of the mouth will normally elicit this reflex and thus test three different cranial nerves.

Facial nerve palsy

Facial nerve palsy (cranial nerve VII). Aetiologies include Bell’s palsy (unknown aetiology first described by Sir Charles Bell) which is a lower motor neurone lesion of the main nerve that can be diagnosed precisely by careful evaluation as to whether the stapedius, petrosal nerves and chorda tympani are involved. More distally in the nerve’s course, branches may be damaged in parotid surgery or submandibular gland surgery where the marginal mandibular branch can be severed. Stroke may also cause upper motor neurone 7th nerve palsy.

Extradural haemorrhage

Extradural haemorrhage in the skull is usually due to trauma at the pterion (the thinnest part of the calvarium or skull vault on its lateral aspect more anteriorly), which causes tearing of the middle meningeal artery or of one of its divisions. Depressed and diastatic skull fractures (fractures along the line of sutures with their widening, seen in infants) may be associated with extradural haemorrhage. The typical appearance on CT is of a lentiform high attenuation area of blood clot localised due to the tethering of the dura at the sutures.

Epistaxis.

Epistaxis. Nose bleeds are most commonly found on the anteromedial septum (Little’s area), a site of rich anastomoses (Kiesselbach) between the anterior ethmoidal, greater palatine, sphenopalatine and superior labial arteries (branches of the ophthalmic , maxillary and facial arteries).

Endotracheal intubation

Endotracheal intubation is indicated when there is inadequate oxygenation not corrected by supplemental oxygen supplied by mask or nasal prongs, inadequate ventilation (increased arterial PCO2), when there is a need to control and remove pulmonary secretions (bronchial toilet) or to provide airway protection in a patient with a depressed gag reflex (for example during general anaesthesia). Severe airway trauma or obstruction warrants emergency cricothyroidotomy. When intubating a patient, there are certain bare essentials that must be present to ensure a safe intubation. Suction, oral Airway that lifts the tongue off the posterior pharynx, the lighted Laryngoscope and endotracheal Tube (SALT)

Craniotomy

Craniotomy is the surgical removal of a section of bone (bone flap) from the skull for the purpose of operating on the underlying tissues, usually the brain. The bone flap is replaced at the end of the procedure. If the bone flap is not replaced, the procedure is called a craniectomy. A craniotomy is used for many different procedures within the head, for trauma, tumour, infection, aneurysm and diagnostic biopsy.

Cleft lip and palate

Cleft lip and palate are a part of the craniofacial anomaly spectrum. Oral clefts are one of the most common birth defects. During normal fetal development between the 6th and 11th week of pregnancy, the clefts in both lip and palate fuse together. In babies born with cleft lip or cleft palate these splits have failed to fuse. Clefts in the lip can range from a tiny notch or a large defect in the upper lip to a split that extends into the nose. A cleft palate can range from a small malformation that results in minimal problems to a large separation of the palate that interferes with eating, speaking, and even breathing. Complications include breathing and feeding difficulties, ear infections and hearing loss, speech and language delay and dental problems.

Corneal reflex

Corneal reflex is closure of the eyelid after stimulation of the thin anterior transparent membrane of the eye and is controlled by two cranial nerves: the sensory component is via the ophthalmic division of the trigeminal nerve (cranial nerve V) and the motor component (closing of the eye) by the facial nerve (cranial nerve VII).

Cervical lymph node enlargement

Cervical lymph node enlargement. In young people, any infection in the head and neck can cause lymph node enlargement, the most common site being the jugulodigastric nodes located just below the angle of the jaw (a). In older patients, it is important to exclude metastases from head and neck cancer. Other causes of cervical lymphadenopathy include TB and lymphoma. A systematic approach to examining all areas of the neck is important in the general examination process. Adenopathy can be demonstrated on CT scanning, which is commonly used in the staging of lymphoma.

NB lymphoma staging includes bone marrow aspiration, assessment of liver and spleen and whole body scanning to assess lymphadenopathy.

Central retinal artery occlusion

Central retinal artery occlusion is caused by a small thrombus or embolus within this branch of the ophthalmic artery. Blindness ensues unless there is immediate treatment. Typical features include opacity of the central retina producing a characteristic cherry red spot macula and cotton wool spots underlying the vessels

Cavernous sinus thrombosis

Cavernous sinus thrombosis. Owing to the great number of structures passing through or in the lateral wall of the cavernous sinus, a blockage or infection in this region has serious consequences which may include damage to the third, fourth, fifth and sixth cranial nerves. Infections around the face and forehead may travel into the cavernous sinus, via the ophthalmic veins.

Carotid endarterectomy

Carotid endarterectomy is the removal of an atherosclerotic plaque from the narrowed lumen of common and internal carotid arteries. This is a good prophylactic measure to reduce the incidence of strokes.

Carotid artery bruits

Carotid artery bruits. Extra and abnormal sounds heard through the stethoscope just lateral to the larynx are often the result of turbulent arterial blood flow due to stenosis of the carotid arteries. Diagnosis is often made non-invasively by colour Doppler ultrasound or magnetic resonance angiography (MRA). Stenosis or occlusion often occurs near the common carotid bifurcation.

Branchial cleft cysts

Branchial cleft cysts are the most common congenital cause of a neck mass. They are epithelial cysts, which arise anterior to the superior third of the sternocleidomastoid muscle from a failure of obliteration of the second branchial cleft in embryonic development. The second arch grows caudally and, ultimately, covers the third and fourth arches. The buried clefts become ectoderm-lined cavities, which normally involute. Occasionally this process is arrested and the entrapped remnant forms an epithelium-lined cyst sometimes with a sinus tract to the overlying skin. Many branchial cleft cysts are asymptomatic but some may become tender, enlarged, or inflamed, or they may develop abscesses that rupture, resulting in a purulent draining sinus to the skin or pharynx – surgery is indicated in these cases.

Burr holes

Burr holes through the skull have been performed for many years (trephination), originally 'to let out the evil spirits', and are now used by neurosurgeons to release blood and thus reduce the intracranial pressure.

Anosmia

Anosmia is loss of the sense of smell commonly related to the nasal and sinus congestion of rhinosinusitis or following head trauma and resultant shearing damage to the olfactory nerve fibres.

Blow-out fractures of the orbit

'Blow-out' fractures of the orbit are usually produced by direct trauma to the upper face. The eye itself is rarely ruptured but the thin orbital floor is often fractured and the eye and its surrounding fat are pushed into the roof of the maxillary sinus – the depressed fracture of the orbital floor can be seen as the 'teardrop sign' on X-ray (a). The inferior rectus muscle can be trapped in the fracture preventing upward gaze (b) causing double vision (diplopia) on looking upward.

Adenoid enlargement.

Adenoid enlargement. The adenoids lie on the posterior nasopharyngeal wall near the openings of the auditory tubes. If repeatedly infected they may cause prolonged otitis media and need to be removed to allow aeration of the middle ear by the auditory tube.

An acoustic neuroma

An acoustic neuroma (vestibular schwannoma or neurolemmoma) is a benign tumour of the eighth cranial nerve. This nerve leads from the inner ear to the brain. Whilst a proportion of tumours will not grow or grow very slowly, growth will ultimately result in brainstem compression (as in this example), hydrocephalus, and brain stem herniation and death. It is diagnosed on MRI with gadolinium contrast as shown. The neuromas extension into the right internal auditory meatus can be seen on coronal MRI. The exact cause is unknown – most people with acoustic neuromas are diagnosed between the ages of 30 and 60. Due to advances in microsurgery, including intraoperative monitoring of facial and cochlear function, the risks of facial paralysis and hearing loss have been greatly reduced – many tumours can now be treated effectively with both surgery and targeted radiation therapy (gamma knife). The outcomes for small acoustic neuromas are better while those larger than 2.5 cm are likely to experience significant hearing loss post surgery.

Accommodation reflex

Accommodation reflex is contraction of the pupil when trying to focus on a near object and is controlled by the parasympathetic nerve fibres carried in the third cranial nerve (oculomotor nerve) from the Edinger–Westphal nucleus of the midbrain (synapse in the ciliary ganglion) which act on the sphincter pupillae muscle to cause reduction in pupil diameter and on the ciliary muscle to cause relaxation of the suspensory ligament, allowing the lens to adopt a more spherical shape for near focusing.

Accessory nerve palsy.

Accessory nerve palsy. Clinically this refers to paralysis of the spinal-originating fibres of the accessory nerve (eleventh cranial nerve) which innervates the sternocleidomastoid and trapezius muscles. The spinal portion is more commonly damaged in the mid-portion of the posterior triangle of the neck (a) where it courses superficially just underneath the fascial roof where it can be damaged from stab wounds or iatrogenically from lymph node biopsy (b). Other pathologies such as posterior triangle abscess (c) or malignant nodal involvement can also cause paralysis of the trapezius muscle, with weakness in shoulder raising and a permanent droop on that side. Where the nerve is damaged proximal to the sternocleidomastoid muscle (which the nerve pierces) difficulty in turning the head towards the opposite side is experienced.

Abducent nerve palsy

Abducent nerve palsy. The abducent nerve (sixth cranial nerve) innervates only the lateral rectus muscle of the eye, and damage results in an inability to move the eye laterally in the horizontal plane. This symptom may be an indication of increased intracranial pressure, owing to the long intracranial course of the sixth nerve.