Adobe Systems Department of Biophysics, Medical Faculty, Masaryk University in Brno 1 Lectures on Medical Biophysics Magnetic resonance imaging (MRI) Infrared imaging (thermography) Adobe Systems Magnetic resonance imaging Infrared imaging ØThe common feature of these imaging methods is the use of non-ionising radiation and the absence of genetic damage. ØMagnetic resonance imaging (MRI) is one of the most advanced imaging methods which gives both morphological and physiological (functional) information. The first MR image (cross-section of chest) was obtained by R. Damadian in 1977. ØInfrared imaging is a functional imaging method giving pictorial information on body surface temperature and thus level of metabolism. It is absolutely safe for the patient as the images are produced by IR radiation given out by the patient himself. First infrared cameras appeared in late 60‘ of 20th century. Adobe Systems MRI Adobe Systems Spin ØSpin is a specific property of sub-atomic particles (electrons, protons etc) like electric charge and mass Ø ØSpin has some strange properties! ̶electrons, protons and neutrons all have the same spin i.e., 1/2 ̶pairs of particles of a single type (e.g., 2 electrons or 2 protons or 2 neutrons) can have a total spin of zero! ̶particles having non-zero total spin act like small magnets (we say they have a ‘magnetic moment’) and their energy is affected if placed in a magnetic field ̶ Adobe Systems Total Nuclear Spin (I) ØIn MRI we are interested in the spin of NUCLEI ØIn medicine, we use the magnetic properties of mainly light nuclides like hydrogen 1H, phosphorus 31P, carbon 13C, fluorine 19F or sodium 23Na to get anatomical or physiological information. Adobe Systems MRI Theory ØThe magnetic moment m of a nucleus is proportional to its angular momentum S (m = gS, g is the gyromagnetic ratio) which depends on the total nuclear spin I. Ø ØIn the absence of an external magnetic field, the magnetic moments of nuclei have all possible (random) directions with the result that: ̶The vector sum of the nuclear magnetic moments in a unit volume of a substance, i.e. the magnetisation vector, is equal to zero ̶The energy of all nuclei is the same Adobe Systems H Nuclei in a Uniform Magnetic Field B ØWhen hydrogen nuclei are placed in an homogeneous strong magnetic field with magnetic flux density B: ̶Their individual magnetic moments will precess with an axis parallel to the direction of B and orientate themselves either in the same direction or in the opposite direction to B. ̶Therefore they have only two possible energies (a higher and a lower energy state). ̶The angular frequency of rotation of this precession (i.e., number of revolutions per second) - is called the Larmor angular frequency w and is given by : w= g B g = gyromagnetic ratio The hydrogen nuclei in the body precess at about 42.6 MHz if B = 1T • orientacemagnet Adobe Systems Magnetisation Vector MGPROTON P - hydrogen nucleus (proton), B - magnetic flux density, z - axis identical with axis of precession (parallel with B), m - magnetic moment of nucleus, mL - component of the magnetic moment of nucleus in z axis (vector sum of these projections in unit volume of a substance is the longitudinal magnetisation vector), mT – projection of m in xy plane (vector sum of these projections in unit volume is the transverse magnetisation vector). Adobe Systems Measuring H(ydrogen) Density in Tissues For H nuclei in the lower energy state to move to the higher energy state RF pulses of frequency equal to the Larmor frequency must be transmitted towards the patient using a transmitter coil (hence the ‘resonance’ in MRI). When this occurs the nuclei are also forced to precess in phase. Longitudinal magnetisation vector becomes oriented in opposite direction Transverse magnetisation vector appears and rotates in plane xy. The return to the ground state (relaxation) is accompanied by the emission of a quantum of electromagnetic energy, which is when detected by an antenna (receiver coil) - the nuclear magnetic resonance (NMR) signal. The signal is relatively strong since the nuclei are precessing in phase. The amplitude of the pulse is proportional to the H density in the tissues (often known as ‘spin density’) . Adobe Systems Relaxation times ØWe have two relaxation times: ØT1 – longitudinal (spin – lattice) - time necessary for return of the “population” of nuclei to the ground state. In biological media: 150 - 2000 ms. Longitudinal magnetisation vector returns to original direction during this time. T2 – transversal (spin – spin) - 2x - 10x shorter than T1. After this time interval the precession movement of individual nuclei is not in phase again. Transverse magnetisation vector disappears after this time. Adobe Systems MRI - Magnetic Resonance Imaging ØTo recognize signals from the different parts of the patient magnetic field gradients („gradual change“) are used e.g., a gradient of B along the z-axis allows us to identify signals coming from different slices of patient perpendicular to the z-axis. ØThe final image is produced using similar types of image generation processes as in CT. ØWe can visualise differences in local hydrogen density or differences in relaxation times. Adobe Systems Technical aspects ØUp to values B = 0.3 T we can use giant permanent magnets (cheap but low contrast resolution). ØElectromagnets are stronger but need a lot of electric energy. ØBest contrast resolution but also the highest operational costs is obtained with magnets having superconducting coils, which can produce fields of up to B = 10 T today, but must be cooled by liquid helium. Typical values of B used in practice are 1 – 3 T. ØGradients (about several mT·m-1) of magnetic field are formed by additional coils. Adobe Systems MR Contrast and MR Spectroscopy ØSome paramagnetic atoms can amplify the signal. That is why e.g., gadolinium is used as a contrast agent for MRI. Gadolinium is chemically bound to certain pharmaceuticals e.g., DTPA - diethylen-triamin-penta-acetic acid. ØThe exact value of the Larmor frequency changes slightly (shifts) according to the position of the hydrogen in the molecules. For example, different shifts of H in groups =CH- or -CH2- are well measurable. This allows us to identify such groups using in-vivo MR - spectroscopy is a powerful tool with application in functional MRI (analysis of ATP content etc.). ØMRI devices are usually adjusted to the resonance of hydrogen atoms present in water molecules. Adobe Systems Safety aspects ØThe magnet can impair function of other medical devices. Hence MRI is strongly contraindicated in patients with some electronic devices inside their bodies (pacemakers, cochlear implants etc.) ØIron objects are strongly attracted to the “gantry” – they can damage the device and cause injuries. MRI is strongly contraindicated in patients with any iron bodies inside (implants, bullets, splinters of grenades etc.) ØMRI is not recommended in the first trimester of pregnancy. ØSome minor problems can be caused by any metals inside the body or on the body surface (heating, prickling sensations). For example: jewellery, some mascaras, old tattoos, tooth fillings, dental crowns and frameworks, implants etc.) ØSome patients are anxious or unquiet inside the device gantry, because of strong noise during the examination. Claustrophobia is also common. Adobe Systems Important Advice magnetic memories (e.g., credit cards) can be destroyed if taken into an MRI room!!!! MRI Devices MR_2 MRI2 Adobe Systems Transversal image of the brain Adobe Systems MR - Angiogram http://www.cis.rit.edu/htbooks/mri/inside.htm an03 Adobe Systems Sagittal section of cervical spine MRI krční páteř Adobe Systems Sagittal section of knee ex03 Adobe Systems 3D model of curvature of left A. cerebri media (arrow) and M1 segment of the same artery (wedge) B) other view on this model shows also curvature of A. cerebri media (arrow shows a well visible aneurysm) These are not plastic models but the result of real MRI image processing! fig1b fig1c •http://splweb.bwh.harvard.edu:8000/pages/papers/shin/ns/ns.html#Outcome: Adobe Systems Continuous browsing of transversal images of a body section, „gif“ (examination of pancreatic duct) Výsledek obrázku pro MRI angio gif https://www.healthcare.siemens.com.au/magnetic-resonance-imaging/options-and-upgrades/clinical-appl ications/syngo-space Adobe Systems Thermography Adobe Systems ØThe contact-less thermographic method is based on the measurement of infrared radiation (IR) emitted by the surface of the body. ØDigital sensor technology is used for image recording. ØWavelength 780 nm - 1 mm ØIR visualised first by Holst in 1934 ØDiscovered by astronomer Herschel in 1800 ØThe wavelength used in thermography 0.7 - 14 μm What is infrared imaging and infrared radiation? Adobe Systems A digital camera with an IR-sensitive pixel sensor array (microbolometer). Microbolometer is a grid of vanadium oxide or amorphous silicon heat sensors atop a corresponding grid of silicon. IR radiation from a specific range of wavelengths strikes the vanadium oxide and changes its electrical resistance. This resistance change is a measure of the temperature. Temperatures can be represented graphically. The microbolometer grid is commonly found in many sizes e.g., 244 x 193 (Meditherm), 160×120 array (Fluke). Principle of image recording Adobe Systems fluke příslušenství Fluke Ti30 Accessories The first IR camera of Department of Biophysics [USEMAP] Adobe Systems ØHigh temperature and spatial resolution ØTemperature distribution is displayed in the form of isothermal lines - isotherms ØPossibility to display temperature profiles ØFast measurement ØSurface temperature distribution differs even in healthy people ØWe have always to compare temperature of symmetrical body parts ØIn contrast to original expectation, it is not possible to use IR imaging as a screening method for malignancies, e.g. breast tumours, because of its low specificity. IR imaging in medicine – advantages and disadvantages Adobe Systems Clinical Importance of Thermography The method informs us about the extent and dynamics of any pathological process which is accompanied by increased temperature. Indications -Diseases of peripheral blood vessels -Diseases of thyroid -Diseases of lymphatic system -Joint inflammations -Demarcation of burns and frostbites -Assessment ob blood supply after reconstruction surgery... Imaging conditions: Temperature of darkened room 20 °C Acclimatisation time about 20 min. Examined body area must be uncovered during acclimatisation. It is not allowed to smoke, drink alcoholic beverages, exercise or take drugs causing vasodilatation or vasoconstriction before examination. Clinical Thermograms obličej2 obličejčz Different palettes of colours (Fluke) hlava Human face (better quality camera) Adobe Systems Thermogram of fingers before and after cold test (Fluke) normprsty chladtest prsttep Finger inflammation after a small injury (FLUKE Ti30) Thermography in surgery C:\Users\Bernard\Desktop\platina\termokamera\Střevo\clanek\06line.tif IR_1835.jpg Stent heating by means of a radiofrequency ablation device (an experiment) Identification of an intestinal segment for resection (an experiment) Themography of ischaemia Left: an acute case of ischaemia in a patient with ischaemic lower limb disease. Right: left hand with paresis of n. ulnaris demonstrated by lowered skin temperature. 4a 2 4b Pictures:www.mhs5000.com/software.htm. Adobe Systems doublebreast img26 Stress fracture on football player X-ray showed no abnormality, thermography correlated well with the patients report of pain and provided justification for the more invasive test of scintigraphy which clearly showed a stress fracture in the exact location indicated by the thermogram. www.dititexas.com/page6.html www.mhs5000.com/software.htm [USEMAP] Adobe Systems Use of the IR Camera for Safety Studies Oven leaking heat – checking heat devices pec pecfoto Overheated cable energetika2 Thermography in construction engineering – house leaking heat Výsledek obrázku pro thermography of houses Adobe Systems Low quality insulation of a warm water piping in area of joints (Fluke) izolace pracuje sonofr Ultrasonographic probe (Fluke) Probe in operation 28,3 °C Probe „frozen“ 26,5 °C Thermal spot left by ultrasonographic probe on the forearm + cooling effect of the coupling gel (Fluke) otissk1 Adobe Systems Last revision October 21, soundtrack added October 20