Topic 2- Diagnostic Techniques

Techniques which produce images to investigate appearance of internal organs which otherwise could not be examined without opening the body surgically.

Radiographers.

The main advantage of all imaging techniques;

• Non-invasive
• Not involve penetration of patients body so cause no physical discomfort or pain.

When is it used?

• Scan a foetus in womb around 12th and 20th week into pregnancy to provide information of if there is more than one foetus, the stage of development and the presence of any neural tube defects such as Spina Bifida.

• Can help a practitioner position a needle accurately e.g. during amniocentesis or CVS.

• Observe condition of organs e.g liver and kidneys/ detecting kidney stones

How does it work?

• Uses a transducer probe which produces high frequency sound waves which penetrate through soft tissue due to their short wavelength. The transducer is placed on the skin and an oily gel is used to ensure there is good contact between trasnducer and skin. The reciever detects the sound reflected from surfaces inside the body. This is sent to a computer which has software to process the data and produces a real time moving image of the tissues. It can detect any abnormalities such as kidney stones/gall stones, liver and is used in pregnancy.

Advantages-

• Low risk of harm as no radiation so can be used when x-rays can't e.g. observing a foetus.

• Produces real time moving image.

• Inexpensive comapred to MRI scans.

Disadvanatges-

• Poorer quality image and less detailed than MRI scans etc.

• Cannot penetrate bone so can't scan the brain.

When is it used?

• To look at certain denser structures inside the body such as bones, masses etc.

• To look at fractures and broken bones etc.

How does it work?

• It uses electromagnetic radiation. X-rays have extremely short wavelengths so can penetrate soft tissues but not metal or thick bone.

• The x-ray machine produces an invisible beam of x-rays which are directed at a specific part of the patients body. Underneath this part of the body is a sheet of photographic paper in an envelope. The x-rays pass through the body and the envelope to cause a change in the photographic paper. More x-rays pass through soft tissue than bone so a shadow of the bone is cast on the paper. The paper is then developed like an ordinary photographic negative and the x-ray is produced.

• The negative shows bones as light and soft tissue as dark because denser tissues such as bone and heart muscle absorb more of the radiation than soft tissues do.

• The practitioner holds up the x-ray to an illuminated panel and examines it.

• A mammography is a type of x-ray and looks for signs of abnormalities in women's breasts. The breast is pressed slightly flat between 2 plates and photographic plate exposed to x-rays- resulting image is a mammogram.

Advanatges-

• Quick and easy- negatives develop while patient waits.

• Cheap compared to other imaging techniques.

Disadvantages-

• Radiation can cause damage to the body- could lead to cancer.

When is it used?

• Imaging bones to diagnose fractures.

• Examine softer tissue structures such as abnormalities of the heart and lungs which would normally show up as dark shadows on a normal x-ray.

• Can observe and image hollow or fluid filled organs such as stomach or intestines.

How does it work?

• Put a contrast medium in patients digestive system which is a liquid containing metal (barium sulphate), salts that are opaque to x-rays known as a barium drink/meal. It looks like a milkshake and tastes quite chalky.
• Some time needed for it to reach part of body that needs to be imaged e.g. stomach.
• Alternative way is for the barium sulphate to be pumped through the rectum (barium enema) which is used to image lower regions of digestive tract e.g. large intestine.
• Area being imaged full of barium sulphate and x-rays cannot penetrate through this and image produced will give a clear white outline.
• When radiation from x-ray machine is emmited to persons body tissue, x-ray detected on photgraphic paper and the monitor.
• X-ray turn black where the x-rays reach photographic paper
• The contrast will show up abnormalities in part of body that is being x-rayed as white.

Advantages-

• Quick and easy compared to CT- negatives developed while patient waits.

• Cheap compared to other imaging techniques.

Disadvantages-

• Radiation can cause damage to body- lead to cancer.

• Takes longer than an x-ray.

When is it used?

• Uses x-rays to produce an image or slice or cross section of the body to produce a digital image which has a 3D view. 

• Diagnose conditions- e.g. damage to bones, injuries to internal organs.

• Monitor conditions.

• Determine size, location and shape of tumour.

• Used on brain (3D image of it's structure) and harder tissues.

How does it work?

• Patient lie on a table which gradually slides in to a cylinder containing the scanner.

• Scanner rotates around patient and emits pulses of x-rays and recieves whatever radiation has passed through the body.

• Information from a set of x-ray recievers is processed by a computer and creates a digital image by building up the sections/slices into a 3 dimensional picture.

Advantages-

• 3D image.

• Clearer picture than other imaging techniques.

• Can be used on the brain.

Disadvanatges-

• Exposure to x-rays is dangerous.

• Equipment is expensive so more difficult to obtain than a conventional x-ray.

• Claustrophobia- doctor need to inform you before CT scan.

When is it used?

• Examine almost any part of the body including brain and spinal cord, bones and joints, heart and blood vessels and internal organs etc.

• Results of scan can help diagnose conditions and plan treatments.

How does it work?

• Patient needs to remove metal objects (jewellery) and asked if they are claustraphobic. The patient will lie on a narrow table which slides into a horizontal cylinder and lie still while image is taken.

• An electromagnet produces a current which forms a strong magnetic field in the cylinder and causes protons (charged particles in hydrogen atoms) to align parallell with eachother.

• This sends a pulse of radiowaves which causes a loss of alignment. 

• As particles realign they produce radiosignals which a reciever detects and creates an image of the part of the body as cross-sections which combine to produce a 3D image by computer.

• Tissues which contain many hydrogen atoms (fat) produce a bright image.
  
• Tissues which contain little or no hydrogen atoms (bone) appear black.

Advantages-

• Very detailed image.

• Clear 3D image.

• Good contrast between abnormalities and normal tissue.

Disadvantages-

• Expensive.

• Noisy.

• Patient can feel anxiety being in the cylinder.

When is it used?

• Looks at functioning in the body to e.g. diagnose cancer or look at brain activity for alzheimers or investigating location and extent of strokes.

Scientific Principles-

• It uses gamma rays- gamma radiation is produced by radioisotopes.

• Makes use of positively charged particles- subatomic particles (positron) which decay quickly in the body and combined with other elements to make radioactive forms of substances found in the body. 

• They are called radionuclides which are radioactive forms of isotopes of common elements (carbon, oxygen, glucose etc.) and are introduced through a drip (IV) into the vein and each tracer/isotope is tailored to a specific function in the body.

• A time interval is allowed to wait for the body to uptake this.

• Hot spots= bright colours.

How it's carried out?

• First, patient is injected with isotope via IV and the isotope is broken down in the body and positrons are emmited= release of gamma rays. Patient lies on table and slides into scanner. The reciever detects the emmited radiation and a computer processess cross sectional information. A coloured image is produced with the brightest colours (red and yellow) indicating the more radiation (more activity)= hot spots. Where the more substance is used this shows fucntion is normal.

Advantages- 

• Only imaging technique that tells you functioning in the body.

• More effective in detecting malfunctions in the brain than other methods.

Disadvantages-

• Expensive compared to e.g. x-rays.

• Have to have an injection.

• Radioactivity so risk of radiation.

• Help to diagnose disorders in the circulatory system e.g. heart arrhythmias (irregular heartbeat) and heart attacks (myocardial infarctions.)

• Electrodes attached to patients skin (chest, wrist or ankles) using sticky pads. Wires link the electrodes to a machine that records the electrical activity of the heart. Recording of this activity called electrocardiogram and examined by a cardiologist. 

• Electrical activity caused by nerve impulses that trigger contractions in different parts of the heart muscle and recording shown on either wavy line on paper or moving line on monitor screen. Wave points on wave pattern= P Q R S T describe various actions of heart as different chambers contract.

• Healthy heart= typcial wave shape. Deviations from this shape or differences between different beats of an individual heart= damage to heart muscle tissue or irregular nerve signals that produce arrhythmias.

• Electrodes on chest collect data related to activity of heart muscles and electrodes elsewhere on body reveal activity of arteries and veins. Malfunctions may only be observable when heart is working quite hard so electrocardiography used while patient walks on treadmill or uses exercise bike.

Advantages-

• Non-invasive- heart studied without major surgery.

• Equipment relatively small and inexpensive.

Disadvantage-

• ECG will likley need further investigation e.g. imaging technique to find what is causing the problem the ECG detected.

Involves taking a sample of living tissue from patient's body for examination usually under a microscope.

There are many different types of tissue biopsies; needle biopsy, punch biopsy, surgery biopsy, smear test and chorionic villus sampling.

The tissues taken in biopsies are examined by cytologists who are trained in detecting abnormal cells.

The biopsies can reveal the presence of abnormal cells which could be cancerous and these would be removed with a scalpel or minor surgery and you may have to be under local anaesthetic or sterilised. They may also be visible when a thin slice of the sample is examined under a microscope.

The sample is often first treated with a staining agent that highlights abnormal cells.

• A hollow needle is inserted into the tissue.

• The needle captures a cylindrical core of tissue which can be extracted and analysed.

• This technique is used to obtain samples of breast tissue in cases where examination or mammography has revealed a lump.

• Uses a large diameter needle to remove a disk of skin arounf 4mm.

• Sample can then be analysed.

• Exposes tissue under the skin which is then cut out for a sample.

• Used where larger samples are required e.g as sometimes in the case of diagnosing breast cancer.

• Involves scraping a small sample of epithelial cells from a membrane.

• For example; cervical smear to diagnose cervical cancer.
• Buccal smerar- sample of cells taken from cheek wall inside the mouth.
• A similar procedure involves using a tiny nylon brush attatched to an endoscope to collect epithelial cells from the bronchi and lungs.

• Involves taking a small tissue sample from lining of the placenta at around 10 weeks into the pregnancy.

• Sample is obtained either by passing a needle through abdomen wall (transabdominal) or inserting a catheter into the vagina and through the cervix (transcervical approach.)

• Slight risk of death of the fetus or the hands or feet of the fetus may become malformed- the risk is smaller with the transabdominal approach as it allows more accurate positioning of the needle due to ultrasound scanning which helps to position the needle or catheter accurately.

• Chromosone analysis of the biopsy gives good indication of presence of chromosonal abnormalities e.g. trisomy 21- downs syndrome in the fetus.

There are many different fluid tests: urine tests, blood tests, mucus tests, amniocentesis.

Other examples;

Cerebrospinal fluid which surrounds and protects the brain and spinal cord.

Synovial fluid which lubricates joints.

Pleural fluid which is found in the lining of the lungs.

• Urine sample done at home, on a visit to GP's surgery or in a hospital.

• Sample tested chemically e.g. to detect level of glucose present. E.g. it can be tested for infectious disease agents such as bacteria by growing cultures from the specimen.

• Can be used to diagnose kidney diseases, urinary tract infections and diabetes and can reveal presence of drugs and abnormal levels of ions such as sodium and potassium.

• Can reveal alot about a patients condition.

• For example,
• levels of glucose which can be important in diagnosing diabetes
• level of cholesterol associated with cardiovascular disease
• the number of red blood cells important in diagnosing anemia.
• can reveal the presence of drugs and levels of nutritionally important minerals such as calcium and iron.

• A complete blood count test is performed by a machine that measures haemoglobin levels and number of red blood cells, white blood cells and platelets per ml of blood. It can provide evidence for viral and bacterial infections, immunodeficiency diseases, vitamin deficiencies, cancers etc.
• Blood samples can be taken by inserting a needle into an arm or vein and drawing out a small volume of blood. If small sample required- blood from a capillary can be obtained by pricking tip of finger. Where information about gas content of blood is needed e.g. oxygen and carbon dioxide levels, a sample is taken from an artery (usually in the thigh.)

• Mucus can be collected from mucus membranes e.g mouth, throat, vagina.

• Cells from mucus sample can be cultured (grown) and examined under a microscope for the presence of bacteria or viruses. 

• Performed around 16th week of pregnancy.

• Needle attatched to a syringe inserted through abdomen so it just penetrates through wall of the womb.

• Sample of fluid withdrawn.

• Ultrasound scanning used to help position needle accurately so it can be kept away from fetus.

• Carries small risk of causing miscarriage.

The amniotic fluid is watery and surrounds the fetus in the womb and is expelled just before a women gives birth. The fluid can aid the diagnosis of a range of chromosonal and genetic disorders e.g. downs syndrome and cystic fibrosis as well as spina bifida.