Instrumentation Flashcards
Survey Meter/ Gas - Filled Detectors: Operating Principals:
Based on ionization of gas molecules by radiations, followed by collection of ion pairs as current with the application of a voltage between two electrodes. The measured current is primarily proportional to the applied voltage and the amount of radiations.
Survey Meter/ Gas-Filled Detectors: Geiger Muller:
Used for detecting Low level beta and gamma rads. Considered of a Geiger muller ( G-M) tube, sensing element which detects radiation, and processing electronic. The GM tube is filled with an instant gas such as helium to which a high voltage is applied. The two briefly contains electrical charge when a particle or proton of incident radiation makes a gas conductive by ionization. The ionization considerably amplified within the tube to produce an easy measured pulse. Operating voltage is around 1000 V.
Survey meter/gas fill detectors: Ionization chamber (cutie pies):
Used for measuring high intensity radiation sources. Contains of a gas fill - chamber,with two electrodes: anode and cathode. A voltage potential is applied between the electrodes to create an electric field in the gas.. when gas between the electrodes is ionized by incident ionizing Radiation, Ion- pairs are created the resultant positive polarity Uber the influence of the electric field. Operating volts is around 50/300 V.
Quality control: frequency and types of checks:
Daily reference checks and performed by measuring a long-lived source using consistent, geometry before each use to verify instrument calibration. Acceptable readings are within + -20% of the calibrated exposure rate.
Quality control: frequent and types of checks
1: battery check: before each use
2: reference check( deducted source): before each use.
3: Calibration: Annually
Quality control: Interpretation and record keeping:
Records of dearly references checks do not need to be kept her ever, the NRC dose require that Records be retained 3 years.
Dose Calibrator: Operating Principles:
One of the most essential instruments in NM for measuring activity of rads for formulating and dispensing rph’s. It’s filled with argon, traces of halogen at high pressure and operating voltage is about 150 V. Because radiations of different types and energies produce different amounts of ionization equals,
activities of different radionuclide generate different quantities of current. The settings of isotope selections are basically the calibration factors for different radionuclides which are determined by measuring the current produced by one mCi.
Quality control: frequently and type of checks:
1: consistency(Daily before use) - (Precision) determines the reproducibility of measurements of a source of known activity from day to day. 2: Linearity of Activity (Quarterly)- how accurate the DC’s measurements are over a wide range, from MCI to UCI. Test involves measuring a source with short half -life over several days. Acceptable range is +-10%. 3: Accurately (Annually)- assesses ability to provide a true measure of activity of radionuclide of different y energies. 2 different long- lived strandards should be used, 1 with a proton energy between 100 and 500 KV. Accessible range is +-10%. 4: Geometric Variation(Instillation)- determinations the effect of sample volume and configuration on the measurement of a sample’s activity.
Interpretation and record keeping:
Records must include the model/serial number of instrument, date of calibration, results, and name of individual, who performed the test. Must be retained for 3 years.
Scintillation Detector System: operating principles:
Basically, gamma rays from a source interact in the NAI(TI) detector and light protons are emitted. The latter strike the photocathode of a photomultiplier (PM) tube and a pulse is generated at the end of the PM tube. The pulse is 1st amplified by a preamplifier and then by a linear amplifier. A pulse height analyzer sorts out the amplified pulses according to the desired energy of the gamma ray and finally feeds the pulse into a scaler, magnetic tape, computer,cathode ray tube or x-ray film.
Scintillation detector System: well Counter:
Used for wipe test to detect very low levels of removal of Contamination. Also use for blood counts, plasma and urine samples.
Scintillation detector systems: Uptake Probe:
Ex: thyroid, surgical: Quantitate activity within a patient.
Quality control: Radionuclide Source:
1: Energies: Well counters: very low levels of radioactivity, sensitivity limits the instruments use of B/C activities greater than 74KBQ(2 uCi) can causes coincidence loss. uptake probe.
2: type of sources;well counter: any activity that can not be spilled; uptake probe Radioactivity’s iodine.
Quality control: Parameters:
1: Energy Resolution: pulse heights of varying amplitudes, representing a range of energies around the photo-peak energy, form the familiar bell- shaped peak. The width of photo-peak is an indicator of the accuracy of the conversation from light to electrical energy, or the energy resolution of the instrument. Cs-137 is used, typical range is 8-12%. The resolution will degrade ( become larger) as the crystal ages or a problem with the amplified or PMT occurs.
2: Efficiency
3: High Voltage calibration:
4: Resolving Time: The shortest time interval between pulses in a nuclear counter that will permit them to be separately detected.
5: Sensitivity: Ability to to detect ionizing events in NaI(TI) crystal expressed in counts per sec/per microcurie(cps/uCi).
6: Energy Linearity: (LET) is term used in dosimetry. It describes the action of radiation upon matter. It is identical to the retarding force acting on a charged ionizing particle transfers to the material traversed per unit distance.
7: Chi-Square: A procedure that checks for random errors greater then those that would be predicted. Random errors affect the reproducibility ( precision) of measurements; always present in radiation counting because of random nature of radioactive decay. Acceptable P values are 0.1-0.9. Values are greater then 0.9 or less then 0.1 indicate variations and the instrument should be checked.
Interpretation and record keeping:
Same as others
Gas and Aerosol Delivery Systems: operating principles:
Air or oxygen is forced through the nebulizer at 30-50 psi to produce Aerosol droplets that are then inhaled by the patient through a mouthpiece. Exhaled air from the patient is trapped in the filter attached to the unit, preventing any contamination of the surrounding area.
Gas and Aerosol Delivery Systems: Exhaust system (EX: gas traps,Xe charcoal Filter): Negative Pressure:
An isolation technique used to prevent cross-contaminations from room to room. It includes a ventilation system that generates negative pressure to allow air to flow into the isolation room but not escape from the room, as air will naturally flow from areas with higher pressure to areas with lower pressure, thereby preventing contaminated air from escaping the room( should be activated when Xe is being used).
Interpretation and record keeping:Gamma Camera: Operating principles(y-camera)
Also called Scintillation camera or Anger Camera, is a device used to image gamma radiation emitting radioisotopes, a technique known as scintigraphy. The applications of scintigraphy include early drug development and nuclear medical imaging to view and analyze images of the human body or the distribution of medically, injected, inhaled, or ingested radionuclides emitting gamma rays. It consists of a call a meter, detector, p.m. tubes; preamplifier, linear amplifier, X/Y positioning circuits, PHA and display or storage.
Gamma Camera: Collimator:
Made of lead with number of different holes of different shape/size,it’s attached to face of a NaI(TI) detector to limit the FOV so that all radiation from outside the FOV prevented from reaching the detector.
Gamma Camera: Detector:
A sodium iodide crystal doped with a very small amount of thallium (NaI(TI) is most commonly used. Other detectors such as bismuth germinate (BGO) and lutetium Oxyorthosilicate (LSO) are also used. The choice of NaI(TI) crystals is due to their reasonable density, high atomic number of iodine (53) that result in efficient production of light photons in the presence of thallium. Most common thickness is 0.95 cm. Increases the probability of complete absorption of y rays(Sensitivity).
Gamma Camera: PM Tubes:
Consists of a light sensitive photocathode at one end, a series of metallic electrodes (dynodes) in the middle and an anode at the other end all enclosed in a vacuum glass tube. Number of PM tubes in a thyroid probe or well counter is one, whereas scintillation cameras vary from 19 to 94 . When a light photon from the NaI(TI) crystal strikes the photocathode, photoelections are emitted which race towards the dynode, strike dynode, create secondary electrons which are further accelerated producing a pulse that is attached to anode.
Gamma Camera: Preamplifier:
The pulse from the PM tube is small and must be amplified with a preamplifier. It is needed to adjust the voltage of the pulse shape and match the impedance levels between the detector and subsequent components to the pulse is accurately processed.
Quality control: Gamma camera: Flood Field uniformity(daily)
Ability of a scintillation camera to produce a uniform image when the source provides a uniform distribution of protons over the Detector. Clinically, it is the ability of the instrument to photons over the images of a radionuclides distribution and patients.
Quality control: High Count Uniformity correction: (Monthly):
The necessary data may be acquired using the same set up as used,for the daily uniformity test,except that; a much larger number of counts ( 60-100 million) must be acquired.
Quality control:Spatial Linearity (Weekly):
Ability of a scintillation camera to produce a uniform image with straight lines corresponding to straight lines in a phantom. Clinically, it is the accurate portrayal of true organ shape. Linearity can also be assessed with along with resolution by examining the straightness of a set of parallel bars.
Quality control: Spatial resolution (weekly):
Ability of a scintillation Camera to separate small objects in space or how much each point in an image is blurred. Clinically, it affects the ability to visualize small defects.
Quality control: Energy resolution (EX: FWHM):
Ability of detector to accurately determine the energy of the incoming radiation. No system is capable of determining precisely , What energy proton struck the Crystal. Instead, the system can only determine within a range of values, what energy radiation it is detecting. Most cameras have a energy resolution in the range of 11% to 13% FWHM at 140 Kev.
Quality control: Detector Sensitivity (Quarterly):
Ability to the detector ionizing events in a sodium iodide crystal expressed in counts per second per microcurie (cps/uCi). It can be affected by incorrect energy settings, incorrect collimation or improper detector to source distance.
Quality control: Extrinsic Versus Intrinsic:
(Part of field uniformity): Extrinsic ( with a collimator) assesses the instrument as it is used clinically. Intrinsic( without a collimator) monitors the condition of the NaI(TI) crystal and electronics associated with the detector.
Quality control center of rotation ( COR )(weekly):
Used to correct for slight variations in the position of the camera head as it rotates. When rotation is perfect, the matrix well always place a pixel in the same location.
