Medical imaging. Medical imaging uses electromagnetic radiation, sound or ingestion of radioactive substances. 10/6/2011 Medical imaging 1

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1 Medical imaging Medical imaging uses electromagnetic radiation, sound or ingestion of radioactive substances 10/6/2011 Medical imaging 1

2 0 Ultrasound Imaging Transducer Reflector Use high-frequency sound (ultrasound) Not audible (typically above 1M HZ ) Piezoelectric crystal creates sound waves Aimed at a specific area of the body Density changes reflect sound waves Echoes are recorded Delay of reflected signal determines the position Works for both still and moving objects Safe! No known tissue damages Very cheap Commonly used to examine fetuses in uterus wrt size, position, or abnormality Also for heart, liver, kidneys, gall bladder, breast, eye, and major blood vessels 10/6/2011 Medical imaging 2

3 X Rays On 8 November 1895, Wilhelm Conrad Roentgen ( ) Was experimenting on emissions generated by discharging electrical current in evacuated glass tubes. To Roentgen's surprise, an object across the room began to glow. This proved to be a barium platinocyanide-coated screen too far away to be reacting to the cathode rays as he understood them. First x ray picture 10/6/2011 Medical imaging 3

4 X Rays for everyone In New York City in 1898, for example, Roentgen's discovery could be seen in 'one portrait" studios, coin operated "amusement machines ("See the bones of your hand for a nickel!!"), at meetings of the Brooklyn Boys X-Ray Club, and in countless electrical and photographic companies. This early X-ray studio, run by electricians, made "bone portraits" for interested clients, as well as attending to the radiographic needs of nearby hospitals. Some authors, like F.T. Addyman, entered into agreements with manufacturers so that a reader could order delivered to his or her home a full set of the apparatus described in the text. 10/6/2011 Medical imaging 4

5 X ray images 10/6/2011 Medical imaging 5

6 Modern X ray imaging Electrons are accelerated by a high voltage and collide with a target (just like a TV tube. As the electrons decelerate they produce X rays and also they knock inner electrons out of the target atoms and when the atom returns to it s ground state X rays are produced of specific energies. The image produced in an X ray is an absorption image, for example, bones absorb more X rays. The main advances in 100 years is to be able to get images with much smaller doses, 10/6/2011 Medical imaging 6

7 CAT scan A CAT scan uses X rays to image a thin slice of the human body. Images are taken of successive slices and computers are used to produce 3 D rotatable images The x-ray tube is at the 1 o'clock position and the arc-shaped CT detector is on the bottom at the 7 o'clock position. The frame holding the x-ray tube and detector rotate around the patient as the data is gathered. 10/6/2011 Medical imaging 7

8 CAT images 10/6/2011 Medical imaging 8

9 Magnetic resonance imaging MRI is an interplay of magnetism and resonance. The body is made up mostly of water and fat. Both of these contain a large number of Hydrogen atoms. These atoms have a spin and act like a magnet If we put the human body inside a large magnet, which has a strength much larger than the magnetic field of earth then the tiny spins of the hydrogen atoms align themselves with the magnetic field, with either N-S and S-N configuration or N-N and S-S configuration. The N-S/S-N configuration takes less energy to align so it is slightly more abundant than N-N/S-S orientation. This gives a net spin vector along the magnetic field (Bo) 10/6/2011 Medical imaging 9

10 Spin alignment In a magnetic field the atoms act like little magnets and line up with the field. There are more parallel to the field because this is a lower energy configuration M N N N N N N N N N N N N N B0 10/6/2011 Medical imaging 10

11 Precession (like a top) In a magnetic field the nuclei do not actually line up with the external field but the direction of the nuclear magnet precesses around the direction of the external field like a top. The frequency of rotation depends on the external field. At 1.0 T the protons spin at approx. 42 million times a second At 1.5T, they spin at approx. 63 million times a second An essential feature of MRI is that there is a magnetic field gradient across the patient so that the precession frequency is position dependent B 0 10/6/2011 Medical imaging 11

12 Levitated daisy Most objects behave aa weak magnets. In this picture a daisy is levitated with the magnet force upwards balancing gravity downwards 10/6/2011 Medical imaging 12

13 MRI in practice The precession frequency depends on the magnetic field and a critical element in MRI is that the magnetic field has a different value at each point in the patient so the precession frequency is different. An RF pulse is sent in with a specific frequency and the protons with that frequency absorb energy. When the pulse stops ( ~ few milliseconds) the protons relax and re emit the energy. This energy is detected as a current in a coil and the characteristics of that current determine the density of protons at that scan point. 10/6/2011 Medical imaging 13

14 MRI images of the brain sagittal Axial coronal 10/6/2011 Medical imaging 14

15 CT and MRI Images CT image of human lungs MRI image of a human head 10/6/2011 Medical imaging 15

16 Compare CT and MRI CT MRI Spatial resolutions Measurement mechanism Slice spacing: mm xy-plane: 0.1 mm X-ray projection Health risk High Low Measurement cost Low High Suitable materials Bones, teeth, lungs, or tissues with injected trace Noise level Relative high Low Slice spacing: 0-10 mm xy-plane: 0.1 mm Nuclear magnetic resonance Soft tissues containing water 10/6/2011 Medical imaging 16

17 Nuclear Medicine Nuclear medicine studies document organ and function and structure, in contrast to conventional radiology, which creates images based upon anatomy. Many of the nuclear medicine studies can measure the degree of function present in an organ, often times eliminating the need for surgery. Moreover, nuclear medicine procedures often provide important information that allows the physician to detect and treat a disease early in its course when there may be more success. It is nuclear medicine that can best be used to study the function of a damaged heart or restriction of blood flow to parts of the brain. The liver, kidneys, thyroid gland, and many other organs are similarly imaged. What is Nuclear Imaging? The process involves injecting into the body a small amount of chemical substance tagged with a short lived radioactive tracer. Depending on the chemical substance used, the radiopharmaceutical concentrates in the part of the body being investigated and gives off gamma rays. A gamma camera then detects the source of the radiation to build a picture. These are called scans.

18 Nuclear Imaging Scans Brain Scans These investigate blood circulation and diseases of the brain such as infection, stroke or tumor. Technetium is injected into the blood so the image is that of blood patterns. Thyroid Uptakes and Scans These are used to diagnose disorders of the thyroid gland. Iodine 131 is given orally, usually as sodium iodide solution. It is absorbed into the blood through the digestive system and collected in the thyroid. Lung Scans These are used to detect blood clots in the lungs. Albumen, which is part of human plasma, can be coagulated, suspended in saline and tagged with technetium. Cardiac Scans These are used to study blood flow to the heart and can indicate conditions that could lead to a heart attack. Imaging of the heart can be synchronised with the patient's ECG allowing assessment of wall motion and cardiac function. Bone Scans These are used to detect areas of bone growth, fractures, tumors, infection of the bone etc. A complex phosphate molecule is labeled with technetium. If cancer has produced secondary deposits in the bone, these show up as increased uptake or hot spots.

19 Radioisotopes Used in Nuclear Medicine For imaging Technetium is used extensively, as it has a short physical half life of 6 hours. However, as the body is continually eliminating products the biological half life may be shorter. Thus the amount of radioactive exposure is limited. Technetium is a gamma emitter. This is important as the rays need to penetrate the body so the camera can detect them. It has such a short half life, it cannot be stored for very long because it will have decayed. It is generated by a molybdenum source (parent host) which has a much greater half life and the Tc extracted on the day it is required. The molybdenum is obtained from a nuclear reactor and imported. For treatment of therapy, beta emitters are often used because they are absorbed locally.

20 Radioactive elements The half life needs to be short so that an image can be obtained in a reasonable time and also that the radioactive dose be non hazardous. Isotopes have to be made close to point of use. Labeling agent carbon-11 oxygen-15 fluorine-18 bromine-75 Half-life 20.3 minutes 2.03 minutes minutes 98.0 minutes The different radioactive elements provide different images.for example oxygen-15 provides an image of how oxygen is being absorbed. Flourine is used to study brain metabolism and carbon for blood flow. 10/6/2011 Medical imaging 20

21 HOW IS TECHETIUM USED FOR A HEART SCAN The test is usually performed at least 12 hours after a suspected heart attack, but it can also be done during triage of a patient who goes to a hospital emergency room with chest pain but does not appear to have had a heart attack. Recent clinical studies demonstrate that technetium heart scans are very accurate in detecting heart attacks while the patient is experiencing chest pain. They are far more accurate than electrocardiogram findings. The technetium heart scan is usually performed in a hospital's nuclear medicine department but it can be done at the patient's bedside during a heart attack if the equipment is available. The scan is done two to three hours after the technetium is injected. Scans are usually done with the patient in several positions, with each scan taking 10 minutes. The entire test takes about 30 minutes to an hour. The scan is usually repeated over several weeks to determine if any further damage has been done to the heart. The test is also called technetium 99m pyrophosphate scintigraphy, hot-spot myocardial imaging, infarct avid imaging, or myocardial infarction scan.

22 The modern gamma camera consists of: - multihole collimator - large area (e.g 5 cm ) NaI(Tl) (Sodium Iodide - Thallium activated) scintillation crystal - light guide for optical coupling array (commonly hexagonal) of photo-multiplier tubes - lead shield to minimize background radiation The Gamma Camera most gamma cameras use thallium-activated NaI (NaI(Tl)) NaI(Tl) emits blue-green light at about 415 nm the spectral output matches well the response of standard bialkali photomultipliers (e.g SbK2Cs ) the linear attenuation coefficient of NaI(Tl) at 150 KeV is about 2.2 1/cm. Therefore about 90% of all photons are absorbed within about 10 mm NaI(Tl) is hydroscopic and therefore requires hermetic encapsulation

23 PET scan Positron electron tomography requires ingesting a radioactive element that decays with positron emission. The positron annihilates with an electron and produces a pair of back to back photons. Since there are many decays in a small volume one can intersect many photon pairs to find the number of photons/unit volume. PET scans are used, for example, to image blood flow in the Brain. 10/6/2011 Medical imaging 23

24 PET Scan for Cancer PET can help doctors locate the presence of cancer/infection anywhere in the body. Because cancers are multiplying and require energy for growth, the PET scan is designed to detect any mass that is growing fast. The PET scan involves the use of radioactive glucose which is injected into the body. The glucose is taken up by the cancer cells and this activity can be monitored by the PET scan. PET scan has the ability to identify tumors in their very early phase. The PET scan can also detect the spread of cancer in other parts of the body. PET scanning is the most sensitive test for detecting cancer and its location. When used in conjunction with other radiological tests like Ultrasound, CT Scans and/or MRI, it is very effective in the detection of cancer or its spread. 10/6/2011 Medical imaging 24

25 PET images Resting Music Visual Thinking PET can be used to study changes in the brain due to different stimuli 10/6/2011 Medical imaging 25

26 SPECT SPECT: Single Photon Emission Computerized Tomography Inject a radioactive chemical Tracer emits gamma rays Capture the emission with a gamma camera Measure metabolic rate (time) Cheap 10/6/2011 Medical imaging 26

27 Summary CT / MRI show that you have a brain PET / SPECT show that you use it! 10/6/2011 Medical imaging 27

28 Medical Isotopes Reactor-produced radioisotopes Chromium-51 Copper-64 Iodine-131 Iridium-192 Molybdenum-99 Phosphorus-32 Samarium-153 Technetium-99m Yttruim-90 Cyclotron-produced radioisotopes Gallium-67 Iodine-123 Thallium-201 Carbon-11, Nitrogen-13, Oxygen-14 and Fluorine-18 Used to label red blood cells and quantify gastro-intestinal protein loss. Used to study genetic disease affecting copper metabolism. Used to diagnose and treat various diseases associated with the human thyroid. Also used in diagnosis of the adrenal medullary and for imaging suspected neural crest and other endocrine tumours. Supplied in wire form for use as an internal radiotherapy source. Used as the parent in a generator to produce technetium-99m, the most widely used isotope in nuclear medicine. Used in the treatment of excess red blood cells. Used with Ethylene Diamine Tetr4amethylene Phosphonate* (Quadramet) to reduce the pain associated with bony metastases of primary tumours. Used to image the brain, thyroid, lungs, liver, spleen, kidney, gall bladder, skeleton, blood pool, bone marrow, salivary and lacrimal glands and heart blood pool and to detect infection. Used for liver cancer therapy. *Only the more commonly used radioisotopes are listed here. Used in imaging to detect tumours and infections. Used in imaging to monitor thyroid function and detect adrenal dysfunction. Used in imaging to detect the location of damaged heart muscle. These are used in Positron Emission Tomography (PET) to study brain physiology and pathology, for detecting the location of epileptic foci and in dementia psychiatry and neuropharmacology studies. They are also used to detect heart problems and diagnose certain types of cancer. 10/6/2011 Medical imaging 28

29 Industrial isotopes Naturally occurring radioisotopes Carbon-14 Chlorint-36 Lead-210 Tritium Artificially produced radioisotopes Americium 241/ beryllium Cobalt-60* Caesium-137 Gadolinium* Gold-198* Gold-198* and technetium-99m* Iridium-192* Iridium-192*, gold-198* and chromium-51* Tritiated water Ytterbium-169* Zinc-65* and manganese- 54* *Manufactured by ANSTO Used to measure the age of organic material that is up to 50,000 years old. Used to measure sources of chloride and the age of water that is up to 2 million years old. Used to date layers of sand and soil laid down up to 80 years ago. Used to measure the age of young groundwater (up to 30 years old). Used in neutron gauging. Used in radiography and gauging. Used in radiotracing to identify sources of soil erosion and depositing; also for thickness gauging. Used in x-ray fluorescence. Used to trace factory waste causing ocean pollution, and to trace sand movement in river beds and on ocean floors. Used to study sewage and liquid waste movements. Used in radiography. Used to trace sand to study coastal erosion. Used as a tracer to study sewage and liquid wastes. Used in radiography. Used to predict the behaviour of heavy metal components in effluents from mining waste water. 10/6/2011 Medical imaging 29

30 Industrial Applications X raying luggage Developing techniques to image containers using neutrons Measuring thickness, controlling fabrication of Plastic film or thin steel. The film runs at high speed between a radioactive source and a detector and the detector signal strength is used to control the thickness of the plastic film. 10/6/2011 Medical imaging 30