Transcript Lecture02 Physical and technological bases radial methods of

Physical and technological
bases radial methods of
diagnostics with use
nonionizing radiations
ULTRASOUND, MAGNETIC
RESONANCE IMAGING (MRI),
THERMODIAGNOSTIC
(THERMOGRAPHY).
DEPARTMENT OF ONCOLOGY
AND RADIOLOGY
PREPARED BY I.M.LESKIV
• For some 60 years (until the middle of
last century) medicine provided the only
practical method of medical imaging.
Isotope scanning was introduced into
medical practice in the 1950s and
ultrasound in the 1960s. CT was
developed in the 1970s and MRI in the
1980s. All these methods advanced
rapidly and are now important specialties
in their own right.
Thus, modern radial diagnostics uses five methods:
Magnetic
resonance
imaging (MRI).
Simple X-rays , CT
Radioisotope scanning
Ultrasound
Thermodiagnostic
(Thermography)
IONIZING
NON-IONIZING
Five methods Radial Diagnostic
IONIZING
X-rays , CT
Radioisotope scanning
NON-IONIZING
MRI
Ultrasound
Thermography
MRI
Typical plan of MRI department
1 – manipulation room
2 – controller room
3
3 - Room of the personnel
1
2
Typical plan of MRI department
Magnet and place of the operator
MAGNETIC RESONANCE
IMAGING (MRI)
1
2
4
MRI consist:
1) a magnet;
2) a table for patient ;
3) Thermal cooler ;
4) a source of a high voltage;
5) a control panel with PS system.
A large cylindrical magnet with an internal diameter large
enough to accept the human body provides an external magnetic
field along the body axis. Gradient coils add a smaller
identification field. The external magnetic field, together with the
gradient field, provides a net external magnetic field, Bo. The
radio frequency (RF) coil provides a force to rotate the spins
away from the direction of the external magnetic field. As the
nuclear spins process back toward the direction of the external
magnetic field, they emit RF signals. These RF signals can be
combined to form an image. Depending on the pulse sequences,
the image can form maps of the proton density or can be used to
form information regarding the local magnetic fields of the
nuclear spins. By varying the RF pulse sequence, the image can
be made up of predominantly Tl information or predominately
T2 information. Tl is known as the spin lattice relaxation time.
Images formed using Tl information are most heavily weighted
toward proton density. T2, called the spin-spin interaction, forms
images that provide information on tissue differences.
MR Signal Characteristics
• CSF: hypointense on Tl WI, hyperintense on T2WI
• Grey/White Matter: Grey matter is grey and white
matter is white on T1WI and relationship is reversed on
T2WI
• Most tumors are hyperintense on T2WI except
Melanoma-hyperintense on Tl WI & hypointense on
T2WI
• FAT—hyperintense on Tl WI, less hyperintense on T2WI
• Flowing blood-Signal void
** How to Remember -Water is White in a T2 scan.
Conversely, a Tl scan shows fat as being whiter.
MRI
Low resolution
High resolution
•
MR contrast media
• Five to ten years ago, contrast media for MR imaging were considered
completely unnecessary. Experience has shown, however, that contrast
media may increase the diagnostic information in several disease states. All
contrast media have magnetic properties, and they change the signal
intensity of the tissues where they are located. The most commonly used
contrast media contain the paramagnetic metal ion gadolinium. These
contrast media are administered by in the body similar to water soluble Xray contrast media.
– Contrast USED IN MRI —Gadolinium DTPA
(V.IMPORTANT)*
– No contrast used in MRCP, MR myelography etc. they
– use Heavily T2 weighted sequences
– Ischaemic Stroke detected earlier on MRI (esp. DW MRI)
– diffusion weighted imaging.
Volumetric reconstruction
MRI
Volumetric reconstruction
MRI in real time
Advantages of MRI
•
•
•
•
•
High soft tissue contrast
No ionizing radiation (Safe in pregnancy)
Multiplanar imaging
Better for bone marrow
All spinal imaging- MRI, posterior-fossa—
MRI.
• Doesn't use iodinated contrast so safe in
iodine allergy
Contraindications and potential
dangers
• No harmfull effects of the static or fluctuating magnetic field used in MR
imaging, have been shown. Ferromagnetic objects are subjected to very strong
mechanical foocer, however, and any ferromagnetic object having a location
where motion of the object may be harmful to the patient represent on absolute
contraidication to MR imaging. The most important and dangerous objects are
ferromagnetic intracranial aneurysmal clips and intraocular ferromagnetic
foreign objects. The main potential donger involved with these objects is
serious haemorrhage. The presence of a pacemaker represents an absolute
contraindication to MR imaging. The function of the pacemaker may be
affected by the magnetic field,and further more, electric currents may be
induced in the pacemaker electrode with possible heating of the endocardium.
•
To avoid harmful heating, the maximum allowable energy transmitted to the
patient is regullated by international recommendations. First trimestrer
pregnancy is (by some considered) due to possible heating of the foetus. An the
first trimester, the foetus. Is surrounded by a relatively large amount of
amniotic fluid, and has litle capability to remove the extra heat.
Magnetic resonance spectroscopy.
• MR units having a magnetic field strength of a least 1.5 tesla, may also
provide the possibility of undertaking in vivo magnetic resonance
spectroscopy (MRS), that con tell the presence and relative concentration
of numerous molecules or metabolites( metabolite).
• Several magnetic atomic nuclei may be used in MRS, but the two most
commonly used nuclei in vivo MRS are hydrogen (1H) and phosphorous
(31P).MR imaging and MR spectroscopy may be combined, c. g. By first
performing (proton) MR imaging for localising purposes. An area of
interest may be selected from MR images before switching to a
phosphorous receiver coil for phosphorous spectoscopy. The result may
be displayed as a frequency spectrum, or may also be shown as colour
coding of areas in the grey scole MR image,the colours indicating the
location and concentration of various phosphorous compounds such as
ATR, ADP,or inorganic phosphalate. Hydrogen(proton)spectoscopy may
also be done,and local concentrations of e.g. lactate indicative of ischmia
may be shown. An vivo MRS thas makes it possible to acquire
information on important metabolic processes in both normal and
pathological tissue, and to follon functional effects of treatment .
ULTRASOUND
DIAGNOSTIC
ULTRASONOGRAPHIC IMAGING
• Ultrasonography is made up of increases and decreases in
pressure with frequency above 20,000 hertz (cycles per second).
A transducer converts electric energy into ultrasonic energy.
The wavelength is the distance between two corresponding
maxima or minima in the ultrasound wave. The frequency of an
ultrasound wave is the number of cycles that pass a point each
second. The period of a wave is the time of one cycle. Pulsed
ultrasonographic imaging sends an ultrasonic pulse into the
body and measures the time of echo return. The distance to the
reflecting surface is related to the time of echo return. Note that
tissues with large differences in acoustic impedance (i.e., physical
density or velocity) produce reflections of almost 100%. Tissueair and muscle-bone interfaces always give large reflections. A
coupling fluid must be used between the ultrasonic transducer
and the patient's skin to avoid 100% reflection from the
transducer-air interfaces.
Modes in USG
• A mode-AMPLITUDE MODE
a.
Ophthalmology
b.
Orbital biometry
• B mode/ GRAY SCALE—For all routine
applications
• M-mode - Echo cardiography
• Doppleroghraphy
• Duplex sonography.
Free Rotational and Slice Selection
Free Rotational and Slice Selection enables you to display any desired anatomical
structure from any selected plane: horizontal, vertical and diagonal. By simply pressing a
button, you choose the angle for image reconstruction. Thus, a better diagnostic
confidence is achieved due to a more accurate visibility.
The relationship between fibroid and amniotic sac,
which is not always recognizable in the conventional
B-mode can be easily seen with Slice Selection
DOPPLER EFFECT
• Principle: described by Christian Johann Dopple Frequency shift of moving object recorded
• Pulsed Doppler-gives the exact velocity waveform
• Colour doppler-Direction Information-blue away from the
transducer, red is towards the transducer**
• Power doppler-SIow Flow detection. Like tumoral
vascularity.
• Common indications of Doppler include PVD, Carotid
atherosclerosis, Portal HT, IUGR, PIH, Renovascular HT
etc.
Advantages
• No radiation / portable
Disadvantage
Operator dependance
Delirious effect on small organism of USG is by acoustic cavitations.
Note—Following investigations do not use ionizing radiation:
a.
b.
c.
Ultrasonography.
Thermography.
MRI.
THERMOGRAPHY
• Thermography – is the method of recording of
a natural heat emission of the body of man in
invisible infrared range of the electromagnetic
spectrum. In present time are designed the
methods of thermography in infrared,
millimeter and decimeter band of wavelengths.
By thermography the special thermal picture of
all sites of the body is defined. In healthy man
it rather constant, and changes at pathological
processes. The method of thermography
absolutely harmless and without any
contraindications.
Technological algorithm of the work
of a thermodiagnostical study
• Preparation of the room and instrumentation to
examination
• Preparation of the patient for examination
• Acquaintance with the case history of the patient and the
results of other examinations.
• Choice of procedure of thermographic examination
• Carrying out of thermographic examination
• Analysis of the thermogram, comparison of the received
diagnostic information with the data of other methods of
investigation
• Formulation of the results and drawing up of the
examination protocol
Preparation of a workroom and
instrumentation to examination
• Before the beginning of every working day the
preparation of the room and instrumentation to
operation is carried out which includes: checkout
of the microclimate of the room, molding of fluid
nitrogen in a recording thermometer, heating,
check and calibration of recording thermometer.
• In the room for examination support a constant
temperature in the range of 19±1°С (and for the
study of dermal circulation 25±1°С) and air
moisture 55-65 %.
Preparation of the patient for examination
• The examination is carried out by fasting, the repeated examinations are carried out
at the same time of day, taking into account the daily temperature variations of the
body
• The examination of the women is carried out on 10-12th day after the beginning of a
menses
• 2 days before examination it is forbidden to apply physiotherapeutic procedures,
mustard plasters, cupping glasses, irritating ointment for the narrowing or dilating of
vessels, cosmetic resorts.
• 1 day before examination do not take remedies for the dilating or narrowing of
vessels.
• At examination of extremities, on the eve, in the evening, it is necessary to have a
bath for taking out of a cornual stratum of the skin, squamous epidermis, shortly to
cut the nails, to take off ногтей a lacquer from the nails if it present.
• For the examination of the head at men it is necessary to have a shave on the eve, in
evening, in order to prevent micro cuts.
• The examination is carried out in recumbent position, but it is also possible to carry
out in a standing position.
Preparation of the patient for examination
• Before examination the explored site of the body is denuded, then the patient adapts
to the temperature of a room during 10-15 mines., and at examination of palms and
foots - 30 mines. In children the convective heat exchange is higher, than in the
adults, and therefore for preventive of chills, examination is carried out at
temperature 26°С. Also children are characterized by more slow thermoadaptation
in comparison with the adults, which lasts near 20-25 mines. For more rapid
adaptation the additional cooling of explored site by means of the fan or substances,
which are quickly vaporized is applied. It enables to receive more contrast
thermographic image. In the period of thermoadaptation the doctor takes the history
of present illness, acquaintes to the results of other investigations, determines the
indications to examination, chooses the method of examination.
• For the increasing of the efficiency of thermography the method of active
thermography is applied, which is based on a different degree of response of a
normal and pathologically changed tissues on physicochemical irritations. The
simplest method for this purpose is the cold test. Cooling of an explored site by an
aerosol of the ethanol during 10 min, or using gauze tampons, wetted with the
alcohol-ethereal intermixture, enables to receive thermogram with a sharp image of
zones of hyperthermia. The method of stress thermography consists in cooling of
arms and forearms in the cold water (+8 - +14°С) during 0,5-2 min. Hyperglycemic
test is based on intravenous introduction of the glucose in organism. The malignant
tumours react to this test by increasing of temperature in affected zone on 0,7-3°С.
The temperature of tumours raises also in conditions of a hyperbaric oxygenation.
The indications to application of
thermography
• By the basic brunch of medicine, where the application of
thermography is effective is the angiologia and oncology.
•
Besides, the thermograph is indicated:
• For the study of the thermo relief of a body of healthy people
• For primary takeoff of the patients, who require the special
examination
• For express-diagnostics of urgent conditions, including acute
inflammatory processes
• For the estimation of innervations and circulation of explored
site
• For observing for the changes of pathological processes and
the results of their treatment.
• Now it is successfully applied in such brunches of medicine, as
surgery, therapy, neurology and eye illnesses, infectious
diseases, cardiology, and other
Methods of thermography
Three methods of thermographic
examination are distinguished:
–а) Contact liquid-crystal thermography
–б) Remote infrared thermography
–в) Remote radio thermometry
Contact thermography
• It is the method, which is based on the properties of the liquid crystals to
change the color depending on temperature. The liquid crystal is the
substances, which in particular temperature range form a liquid phase, which
has simultaneously properties of fluids, and crystalline solids. As the fluids,
they possesses flow ability, as crystals - anisotropy. It is such original
"chameleons" which are capable to change the color depending on temperature
of a surface on which they are put.
• In present time the industry releases the liquid-crystal heat-indicating films,
which represent a dispersion of the liquid crystals in vinyl alcohol, put on a
special elastic black film, or the layer of liquid crystals between two polymer
film, one of which black-colored. The skin before superimposition of the film is
lubricated with Vaseline or glycerin. Such films are reusable. However, at some
pathological states of the skin (combustion, frostbites, some dermal diseases),
they cannot be applied. Also it is impossible to simulate a composite
configuration of the body, to receive plain thermogram by them. Except the
films, the special screens covered with a liquid-crystal composition are released
also. During the thermography the screen comes nearer to a surface of the skin
and the image appears on it.
• Despite simplicity and disposability of the method, it is necessary to note, that
its opportunities are restricted because imperfection of the compound of liquid
crystals and poor assortment of heat-indicating films.
• The recording thermometer consists of
such basic components:
• 1) the scanning mirror;
• 2) the optical system of lenses;
• 3) the receiver of infrared rays;
• 4) the amplifier;
• 5) the computer system of collecting,
processing and reproduction of the
information
Remote radiothermometry (SHFthermometry
• The method is based on measuring of thermal
super high-frequency radiation of the body of the
man in centimeter and decimeter band, which
show the temperature of the deep stratums of
the body.
• Thus, the basic drawback of infrared
thermography - receiving of the information only
from the superficial layers of the body is
liquidated. However, the quality of
instrumentation for this method is still low, that
restricts its application.
Analysis and interpretation of thermogram,
thermosemeiology of diseases
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The analysis and interpretation of thermogram is carried out taking into account the
anamnesis and the general plan of the analysis of the beam images.
First of all, it is necessary to determine the type of the thermogram. There are blackand-white and color thermograms. On black-and-white thermogram the sites, which
have the higher temperature are represented by white color, and lower – by black.
The scale of intermediate tones from white color to black reflects the gradual change
of the temperature from high to low.
On color thermogram the sites with the high temperature have white, yellow, orange
and red colors, and with low - green, blue and violet.
For the description of the thermorelief of the body is necessary to use the terms:
"hypothermal zone", "hyperthermal zone", " isothermal zone ".
For the performance of the homogeneity of this zone it is necessary to use the terms
"homogeneous zone of hyperthermia", "heterogeneous zone of hyperthermia" etc.
For the description of the respective types of thermogram the using of the figurative
terms: " thermo ablation " and " thermo anomaly " is supposed.
The thermographic signs can conditionally be divided on thermo morphological and
thermo functional.
Advantages of thermography
The absolute harmlessness of the method, so it can be applied
in repeated examinations, in children, pregnant women, at
prophylactic examinations.
• High sensitivity of the method. A minimum temperature
gradient between two points apart 1 mm is 0,1°С.
• High speed of examination. Depending on the type of
thermometer the examination lasts 0,5-2 min.
• Ecological safety of instrumentation for examination.
• Opportunity of simultaneous, consecutive examination
practically of all organs and systems of the man.
Limitations s of thermography
• Low specificity of the method. Frankly, this
concepts is closely connected with the
qualification of the personnel. It is considered
that only the specialist, who has carried out
1000-4000 thermogram and possesses the
experience of the analysis and interpretation of
the diagnostic information, which gains at other
methods of radial diagnostics, can correctly
interpret the thermograms.
• Information about thermo relief only of
superficial layers of the body.
Radiation hazards (REMIND)
• X-rays used in conventional radiography and CT, as well as gamma rays and
other radionuclide emissions, are harmful. Natural radiation from the sun,
radioactivity in the environment, together with atmospheric radioactivity
from nuclear bombs and other man-made ionizing radiations contribute a
genetic risk over which an individual doctor has no control. However,
ionizing radiation for medical purposes is of several times greater magnitude
than all other sources of man-made radiation and is under the control of
doctors. It is their responsibility to limit the use of x-rays and other ionizing
radiations to those situations where the benefit clearly outbalances the risks.
Unnecessary radiation is to be deplored. The principle to be used is the socalled ALARA principle: 'as low as reasonably achievable,. This is achieved
by the use of appropriate equipment and good technique - limiting the size of
the x-ray beam to the required areas, limiting the number of films to those
that are necessary, keeping repeat examinations to a minimum and ensuring
that the examination has not already been performed. Just as important as
these factors, all of which are really the province of those who work in the xray department, is the avoidance of unnecessary requests for x-ray
examinations, particularly those that involve high radiation exposure such as
barium enema, lumbar spine x-rays and CT examinations. If possible,
alternative techniques such as ultrasound or MRI should be
considered.