concepts of radiologic science
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1. What is radon?
- is a chemical element with symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless noble gas, occurring naturally as the decay product of uranium. It is one of the densest substances that remains a gas under normal conditions and is considered to be a health hazard due to its radioactivity. Its most stable isotope, 222Rn, has a half-life of 3.8 days. Due to its intense radioactivity, it has been less well-studied by chemists, but a few compounds are known.
Radon is formed as part of the normal radioactive decay chain of uranium. Uranium has been around since the earth was formed and its most common isotope has a very long half-life (4.5 billion years). Uranium, radium, and thus radon, will continue to occur for millions of years at about the same concentrations as they do now.[1]
Radon is responsible for the majority of the public exposure to ionizing radiation. It is often the single largest contributor to an individual's background radiation dose, and is the most variable from location to location. Radon gas from natural sources can accumulate in buildings, especially in confined areas such as attics, and basements. It can also be found in some spring waters and hot springs.[2] Epidemiological evidence shows a clear link between breathing high concentrations of radon and incidence of lung cancer. Thus, radon is considered a significant contaminant that affects indoor air quality worldwide. According to the United States Environmental Protection Agency, radon is the second most frequent cause of lung cancer, after cigarette smoking, causing 21,000 lung cancer deaths per year in the United States.[3]
2. What are different units for radiation?
- Radioactivity is measured in Becquerel (Bq) per second. 1 Bq means one disintegration per second. It is also measured in Curie (Ci), named for Madam Curie, who shared Nobel Prize with her husband. 1 Curie = 3.7 x 1010 Bq or disintegrations per second. The radiation absorbed dose is measured in Gray, rad, rem and Sievert (Sv).
In the United States, absorbed dose is commonly given in rad or Gray and other protection quantities, such as equivalent dose and effective dose, are given in rem. The following table is provided to help avoid confusion among persons not familiar with these quantities. The use of the newer system of units would be particularly useful during radiological incidents involving international responders.
Conversions for Effective Dose, Equivalent Dose, Dose Equivalent, and ambient dose equivalent
0.001 rem = 1 mrem = 0.01 mSv
0.01 rem = 10 mrem = 0.1 mSv
0.1 rem = 100 mrem = 1 mSv = 0.001 Sv
1 rem = 1000 mrem = 10 mSv = 0.01 Sv
10 rem = 100 mSv = 0.1 Sv
100 rem = 1000 mSv = 1 Sv (Sievert)
1000 rem = 10 Sv
Conversions for Absorbed Dose
0.001 rad = 1 mrad = 0.01 mGy
0.01 rad = 10 mrad = 0.1 mGy
0.1 rad = 100 mrad = 1 mGy = 0.001 Gy
1 rad = 1000 mrad = 10 mGy = 0.01 Gy
10 rad = 100 mGy = 0.1 Gy
100 rad = 1000 mGy = 1 Gy (Gray)
1000 rad = 10 Gy
3. What is mSv unit?
mSv stands for milisievert which is equivalent to 1x10^-3 sievert. The sievert (symbol: Sv) is the SI derived unit of dose equivalent. It attempts to reflect the biological effects of radiation as opposed to the physical aspects, which are characterised by the absorbed dose, measured in gray. It is named after Rolf Sievert, a Swedish medical physicist famous for work on radiation dosage measurement and research into the biological effects of radiation.
Measured Dose (Temporary Measurements) – gamma radiation or X-rays
1 R (roentgen) = 0.01 Gy = 0.01 Sv
4. What is multislice spiral CT?
- A detailed picture of areas inside the body. The pictures are created by a computer linked to an x-ray machine that scans the body in a spiral path. Also called helical computed tomography
Computerized tomography and magnetic resonance imaging are routinely performed for the imaging of the adrenal mass and for standard staging of the chest and abdomen as the lung and liver are the primary organs for metastasis in ACC Contrast-enhanced ultrasound has been shown to have a high sensitivity and specifity for the differentiation of hepatic and neuroendocrine tumors. Twelve patients with ACC were treated in our centre from 2004 to 2006. The patients received staging with a contrast-enhanced multislice spiral computed tomography as well as with a conventional and an echo-enhanced ultrasound of the liver. Contrast-enhanced ultrasound demonstrated liver metastases in 8 out of 12 patients and MSCT in 6 out of 12 patients. In 2 out of 8 patients MSCT did not detect the liver metastases. Even in retrospective analysis with knowledge of the ultrasound results, the hepatic lesions were not recognized by the MSCT, but became detectable by MSCT at a later time point. All hepatic lesions diagnosed by MSCT were also seen by ultrasound. The detection of liver metastases by ultra-sound resulted in a change of therapy in two patients. Spiral computed tomography and, more recently, multislice SCT angiography have established roles in studying subarachnoid hemorrhage. Potential advantages in MSCT angiography include rapid acquisition, ready availability, ease of monitoring, high spatial resolution, some temporal resolution, and relative freedom from artifacts. The authors assert that these attributes make MSCT angiography the initial imaging method of choice in the assessment of not just SAH but all intracranial vascular pathophysiologies, particularly in children.Methods. The installation of a MSCT unit sparked the authors' interest in using MSCT angiography and MSCT venography in cases in which they would have formerly performed magnetic resonance angiography, MR venography, or catheter angiography as an initial investigational method. They retrospectively evaluated seven cases in which they had used the former imaging techniques to study intracranial vascular pathophysiologies. All scans were obtained on a Siemens Sensation 16-slice scanner, and postprocessing was performed on a Leonardo Workstation.Results. Multislice spiral CT consistently provided useful vascular imaging of a wide variety of intracranial vascular pathophysiologies and an alternative imaging modality in patients considered to be too unstable for more time-consuming investigations.Conclusions. Review of the angiographic data of 118 live kidney donors was performed to assess the renal vessel anatomy; compare the findings with the perioperative findings using multislice spiral computed tomographic angiography with the use of 50 mL of intravenous contrast; determine the sensitivity of this technique in the workup of live potential renal donors; and finally to discuss and compare the results of the present study with the reported results using single-slice spiral CTA, magnetic resonance angiography, and conventional angiography. Methods. Retrospective analysis of the angiographic data of 118 of prospective live kidney donors was performed. All donors underwent renal angiography on MSCTA scanning using 50 mL of intravenous contrast with 1.25-mm slice thickness followed by maximum intensity projection and virtual rendering techniques postprocessing algorithms. Analysis was made on imaging and intraoperatively for the number of renal arteries as well as their bifurcation pattern, location, vessel caliber, length, and venous anatomy, and these were then compared with each other. Results. MSCTA showed clear delineation of the main renal arteries in all the donors with detailed vessel morphology. The study also revealed a 100% sensitivity in the detection of accessory renal vessels, which had an overall incidence of 26.67%, with the most common distribution in the perihilar region. Conclusions. The present study showed a 100% sensitivity and specificity in the visualization and detection of main and accessory renal vessels with the use of only 50 mL of intravenous contrast with similar results seen with CA which has so far been considered the "gold standard." The results on MSCTA were also better than those with the use of SSCTA and MRA in the workup, of liver renal donors, with the above technique also proving to be more cost effective.
Remarkably, in most of those studies, conventional planar perfusion scans were compared with tomographic images acquired using state-of-the-art CT scanners-a study design that cannot give impartial results. Hence, the aim of our study was a balanced comparison between V/Q lung scintigraphy and CT angiography using advanced imaging techniques for both modalities. Methods: A total of 83 patients with suspected pulmonary embolism were examined using V/Q lung scintigraphy in SPECT technique as well as 4-slice spiral CT Ventilation scans were done using an ultrafine aerosol. Additionally, planar images in 8 views were extracted from the V/Q SPECT datasets. Two experienced referees assessed each of the 3 modalities. The final diagnosis was made at a consensus meeting while taking into account all of the imaging modalities, laboratory tests, clinical data, and evaluation of a follow-up period. In the course of the consensus conference, pulmonary embolism was diagnosed in 37 of the 83 patients. Compared with planar scintigraphy, SPECT raised the number of detectable defects at the segmental level by 12.8% and at the subsegmental level by 82.6%. The sensitivity/specificity/accuracy of planar V/Q scintigraphy and V/Q SPECT was 0.76/0.85/0.81 and 0.97/0.91/0.94, respectively, compared with 0.86/0.98/0.93 for multislice CT Conclusion: SPECT and ultrafine aerosols are technical advancements that can substantially improve lung scintigraphy. Using advanced imaging techniques, V/Q scintigraphy and multislice spiral CT both yield an excellent and, in all aspects, comparable diagnostic accuracy, with CT leading in specificity while SPECT shows a superior sensitivity. Background: Radiation dose exposure is increased in multislice spiral computed tomography compared to conventional coronary angiography.Methods: Retrospective data analysis of 56 patients, heart rate 64 +/- 11 bpm) who underwent MSCT and CXA was performed. The sensitivity of CT in detection of pancreatic tumors is more than 90% when direct and indirect signs are used for diagnosis. However, the potential to differentiate exocrine tumors of the pancreas is limited. CT is used in these lesions to perform an adequate staging, especially for surgical purposes. The operative resectability, primarily in regard to vessels, lymph node metastasis and hepatic metastasis, has to be assessed. Keeping in mind the limitations of this macro-morphological imaging procedure, CT has the best reproducibility and overall accuracy of all imaging methods. Using multislice CT it is possible to perform nonaxial reconstructions with high resolution. In functional endocrine tumors, multislice spiral CT will enhance the diagnostic capabilities, since the whole organ can be examined in thin slices, with high resolution during the rather short arterial phase of the contrast medium. Since some endocrine tumors are hypovascular, a scan during the portovenous phase is recommended too. The diagnosis of benign pancreatic tumors, like serous cystadenoma and pancreatic lipomas, is addressed. The most important pseudotumors of the pancreas are discussed.
Vessel phantoms and 36 patients underwent nonenhanced and contrast-enhanced cardiac multislice-spiral computed tomography. Reconstruction-parameters: slice thickness 3 mm, increment 2 mm, kernels B35f and B30f. The Agatston score, calcium mass, and number of lesions were calculated. Images were scored using detection thresholds of 130 Hounsfield units and 350 HU Based on the Agatston score, risk stratification was performed. In the phantom and patient study, altering the threshold from 130 to 350 HU led to a significant decrease in the mean Agatston score and calcium mass. Contrast-enhanced studies showed an increase of the mean Agatston score and calcium mass when compared with nonenhanced scans. A total of 57% of all patients were assigned to different risk groups.
5. What is high level fluoroscopy?
- is an imaging technique commonly used by physicians to obtain real-time moving images of the internal structures of a patient through the use of a fluoroscope. In its simplest form, a fluoroscope consists of an X-ray source and fluorescent screen between which a patient is placed. However, modern fluoroscopes couple the screen to an X-ray image intensifier and CCD video camera allowing the images to be recorded and played on a monitor.
6. History of crooks tube.
- Crookes tubes evolved from the earlier Geissler tubes, experimental tubes which are similar to modern neon lights. Geissler tubes had only a low vacuum, around 10-3 atm (100 Pa),[6] and the electrons in them could only travel a short distance before hitting a gas molecule. So the current of electrons moved in a slow diffusion process, constantly colliding with gas molecules, never gaining much energy. These tubes didn't create beams of cathode rays, only a pretty glow discharge that filled the tube as the electrons struck the gas molecules and excited them, producing light.
Crookes and his glowing tubes gained notoriety, as shown by this 1902 caricature in Vanity Fair. The caption read "ubi Crookes ibi lux", which in Latin means roughly, "Where there is Crookes, there is light".
Crookes was able to evacuate his tubes to a lower pressure, 10-6 to 5x10-8 atm, using an improved Sprengel mercury vacuum pump made by his coworker Charles A. Gimingham. He found that as he pumped more air out of his tubes, a dark area in the glowing gas formed next to the cathode. As the pressure got lower, the dark area, called the Crookes dark space, spread down the tube, until the inside of the tube was totally dark. However, the glass envelope of the tube began to glow at the anode end.
What was happening was that as more air was pumped out of the tube, there were fewer gas molecules to obstruct the motion of the electrons, so they could travel a longer distance, on average, before they struck one. By the time the inside of the tube became dark, they were able to travel in straight lines from the cathode to the anode, without a collision. They were accelerated to a high velocity by the electric field between the electrodes, both because they didn't lose energy to collisions, and also because Crookes tubes required a higher voltage. By the time they reached the anode end of the tube, they were going so fast that many flew past the anode and hit the glass wall. The electrons themselves were invisible, but when they hit the glass walls of the tube they excited the atoms in the glass, making them give off light or fluoresce, usually yellow-green. Later experimenters painted the back wall of Crookes tubes with fluorescent paint, to make the beams more visible.
This accidental fluorescence allowed researchers to notice that objects in the tube, such as the anode, cast a sharp-edged shadow on the tube wall. Johann Hittorf was first to recognise in 1869 that something must be travelling in straight lines from the cathode to cast the shadow.[7] In 1876, Eugen Goldstein proved that they came from the cathode, and named them cathode rays (Kathodenstrahlen).[8]
At the time, atoms were the smallest particles known, the electron was unknown, and what carried electric currents was a mystery. Many ingenious types of Crookes tubes were built to determine the properties of cathode rays (see below). The high energy beams of pure electrons in the tubes revealed their properties much better than electrons flowing in wires. The colorful glowing tubes were also popular in public lectures to demonstrate the mysteries of the new science of electricity. Decorative tubes were made with fluorescent minerals, or butterfly figures painted with fluorescent paint, sealed inside. When power was applied, the fluorescent materials lit up with many glowing colors.
In 1895, Wilhelm Röntgen discovered x-rays emanating from Crookes tubes. The many uses for x-rays were immediately apparent, the first practical application for Crookes tubes.
Crookes tubes were unreliable and temperamental. Both the energy and the quantity of cathode rays produced depended on the pressure of residual gas in the tube. Over time the gas was absorbed by the walls of the tube, reducing the pressure. This reduced the amount of cathode rays produced and caused the voltage across the tube to increase, creating 'harder' more energetic cathode rays. Soon the pressure got so low the tube stopped working entirely.
The electronic vacuum tubes invented later around 1906 superseded the Crookes tube. These operate at a still lower pressure, around 10-9 atm (10-4 Pa), at which there are so few gas molecules that they don't conduct by ionization. Instead, they use a more reliable and controllable source of electrons, a heated filament or hot cathode which releases electrons by thermionic emission. The ionization method of creating cathode rays used in Crookes tubes is today only used in a few specialized gas discharge tubes such as krytrons.
The technology of manipulating electron beams pioneered in Crookes tubes was applied practically in the design of vacuum tubes, and particularly in the invention of the cathode ray tube by Ferdinand Braun in 1897.
7. What is the difference between ionization and excitation?
- Ionization is the physical process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions. This is often confused with dissociation (chemistry).
The process works slightly differently depending on whether an ion with a positive or a negative electric charge is being produced. A positively-charged ion is produced when an electron bonded to an atom (or molecule) absorbs enough energy to escape from the electric potential barrier that originally confined it, thus breaking the bond and freeing it to move. The amount of energy required is called the ionization potential. A negatively-charged ion is produced when a free electron collides with an atom and is subsequently caught inside the electric potential barrier, releasing any excess energy.
Excitation is an elevation in energy level above an arbitrary baseline energy state. In physics there is a specific technical definition for energy level which is often associated with an atom being excited to an excited state.
In quantum mechanics an excited state of a system (such as an atom, molecule or nucleus) is any quantum state of the system that has a higher energy than the ground state (that is, more energy than the absolute minimum). The temperature of a group of particles is indicative of the level of excitation (with the notable exception of systems that exhibit Negative temperature).
The lifetime of a system in an excited state is usually short: spontaneous or induced emission of a quantum of energy (such as a photon or a phonon) usually occurs shortly after the system is promoted to the excited state, returning the system to a state with lower energy (a less excited state or the ground state). This return to a lower energy level is often loosely described as decay and is the inverse of excitation.
8. What is radiography?
- the use of x-rays to view a cross sectional area of a non uniformly composed material such as human body. By utilizing the physical properties of the ray an image can be developed displaying clearly, areas of different density and composition.
A heterogeneous beam of X-rays is produced by an X-ray generator and is projected toward an object. According to the density and composition of the different areas of the object a proportion of X-rays are absorbed by the object. The X-rays that pass through are then captured behind the object by a detector (film sensitive to X-rays or a digital detector) which gives a 2D representation of all the structures superimposed on each other. In tomography, the X-ray source and detector move to blur out structures not in the focal plane. Computed tomography (CT scanning) is different to plain film tomography in that computer assisted reconstruction is used to generate a 3D representation of the scanned object/patient.
9. What type of injury happened to Clarence Dally?
- After testing his x-ray equipment, his hands got burned and those burns turned cancerous, spread throughout his body and was ultimately fatal.
source: nukes.org
10. How did snook transformer and coolidge tube reduced the injuries?
-The characteristic features of the Coolidge tube are its high vacuum and its use of a heated filament as the source of electrons. There is so little gas inside the tube that it is not involved in the production of x-rays, unlike the situation with cold cathode gas discharge tubes.
The operation of the Coolidge tube is as follows. As the cathode filament is heated, it emits electrons. The hotter the filament gets, the greater the emission of electrons. These electrons are accelerated towards the positively charged anode and when the electrons strike the anode, they change direction and emit bremsstrahlung, i.e., x-rays with a continuous range of energies. The maximum energy of the x-rays is the same as the kinetic energy of the electrons striking the anode. In addition to the x-rays produced at the focal spot of the anode, some undesirable x-rays (stray radiation) are produced by electrons striking other tube components.
The key advantages of the Coolidge tube are its stability, and the fact that the intensity and energy of the x-rays can be controlled independently. Increasing the current to the cathode increases its temperature. This increases the number of electrons emitted by the cathode, and as a result, the intensity of the x-rays. Increasing the high voltage potential difference between the anode and the cathode increases the velocity of the electrons striking the anode, and this increases the energy of the emitted x-rays. Decreasing the current or the high voltage would have the opposite effects. The high degree of control over the tube output meant that the early radiologists could do with one Coolidge tube what before had required a stable of finicky cold cathode tubes. As a bonus, the Coolidge tube could function almost indefinitely unless broken or badly abused.
11. How many xray exams are allowed in a year?
- depends on type of examination because they have different amounts of emitted radiation
Source: radiologyinfo.org
