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Questions tagged [medical-physics]

A field of applied physics dealing with the application of physics to diagnosis and treatment of diseases.

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Permittivity real and imaginary parts with similar value possible?

Here's the context; I'm studying biological tissues that are supposed to behave like dielectrics. Using the modified cole-cole equation for theoretical predictions: $$\tilde{\varepsilon}_r (\omega )= \...
Laurier's user avatar
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23 views

Distribution of scattered photons in cone-beam computed tomography (CBCT)

I am using MCGPU to simulate photon transport in cone-beam computed tomography (CBCT). I ran an experiment, where a water cylinder containing spherical objects was irradiated. The simulation software ...
In the blind's user avatar
1 vote
2 answers
66 views

Intensity wavelength graph random peaks

what do those peaks represent? This being in a situation where my electrons are accelerated and photons being emitted due to deceleration.
Safa yousif's user avatar
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637 views

Why does a CT scan with contrast make you feel warm?

I recently had a CT scan with IV contrast liquid. I was warned it might make me feel warm and that this is normal. I had an amazing sensation of heat moving down my body. All my searches tell me that ...
Skrrp's user avatar
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Efficiency of light collection of a lens

I am trying to calculate the theoretical imaging performance of a scintillator & camera combination, (scintillator is a plane that emits optical light under X-ray exposure). My question is I found ...
bbbeenn32's user avatar
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What is "point of interest" and why isn't there a Zref for determining electron beam quality with TRS 398?

What is "point of interest" and why isn't there a Zref for determining electron beam quality with TRS 398? ((To what depth do you put the ion chamber when you do high energetic electron ...
medical physics's user avatar
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1 answer
81 views

Why is 180 degree pulse applied after half echo time (TE) in Spin Echo sequence?

The definition of Echo Time from Radiopaedia: The echo time (TE) refers to the time between the application of the radiofrequency excitation pulse and the peak of the signal induced in the coil. It ...
HelpNeederStudent's user avatar
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40 views

How (mathematical relation) and why (mechanism) do Time-to-Repetition (TR) and Time-to-Echo (TE) affect Signal-to-Noise-Ratio (SNR)?

I want to understand why (what is the mechanism behind) lowering the time to echo (can we actually have T1-weighted Zero Time to Echo images) increases the Signal to Noise Ratio in (nuclear) Magnetic ...
George Ntoulos's user avatar
4 votes
1 answer
66 views

Absorption respose of cones in eye

I am trying to find information about the absorption response of the cones in the eye to different wavelengths of light. I have noticed two types of graphs and answers: one which shows the S-...
Jbag1212's user avatar
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1 answer
306 views

Medical Linac MeV vs MV

I am currently doing a project on medical linear accelerators, and there's one thing I am having trouble understanding. Why is the electron beam energy measured in MeV, but the x-ray energy is ...
Cillian's user avatar
1 vote
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Physical Interpretation of Flowrate Time Derivative of Incompressible Fluid in Variable Volume Vessel with Single Inlet

I am an academic researcher who studies fluid mechanics of the left ventricle (the primary chamber of the heart that actually pumps blood to the rest of your body). The majority of my work focuses on ...
John's user avatar
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Why take into account deceleration radiation only, but not acceleration radiation when Bremsstrahlung happens?

Why only take into account deceleration radiation rather than the radiation caused by acceleration when going tangent towards the nucleus and acceleration caused by the change in direction when flyby ...
medical physics's user avatar
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Bragg-Gray cavity theory

Why does the Bragg-Gray cavity theory require that all charged particles will not stop in the cavity and dose is solely due to charged particles crossing the cavtiy in the cavity?
jimmy's user avatar
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Charged particle equilibrium and Bragg-Gray cavity theory

About the charged particle equilibrium: 'In a small volume in the radiation field, some secondary electrons generated in the volume escape from the volume, and some electrons generated outside the ...
jimmy's user avatar
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1 answer
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Gamma and X-Ray Shielding with Photoelectric Effect

The photoelectric effect is most probably seen when the incoming light has lower energy than the energy needed for both Compton scattering and pair production to happen. The probability of the ...
medical physics's user avatar
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How much Uranium would a country like Iran need to produce for supplying its Technetium needs?

This is not a question about politics, although the motivation is a political situation. Iran, which enriches Uranium to a level of $60\%$ $\rm{^{235}U}$, is claiming it has civilian uses for this ...
einpoklum's user avatar
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Reverse blood flow in an IV

When the IV drip for a patient is completed, the patient's blood will flow back. This is apparently due to the pressure difference. However, IV needles are inserted into veins in the direction of ...
Starlight's user avatar
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2 votes
1 answer
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6-day curie to grams?

I am a pre-med interested in nuclear medicine. I recently came upon this wonderous radioisotope called Mo-99 (which decays into Technetium-99m), but in their industry, they measure the quantity of ...
Young Jun Lee's user avatar
3 votes
1 answer
55 views

Why does vitrification cause less damage to biological tissue than freezing does?

Long-duration cryopreservation of biological tissue (most often semen, egg cells, or fertilized embryos) is typically done at 77 K, since the samples can be easily kept at that temperature by ...
tparker's user avatar
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107 views

How does CT imaging deal with the thickness of materials?

In the medical CT imaging field, image of an inspected object is obtained through xray projection. xray is attenuated by the inspected object through the formula $I=I_0e^{-\mu t}$. The projection $p$ ...
Winston Pan's user avatar
1 vote
1 answer
76 views

Why does absorbed dose increase with increasing tube potential in computed tomography?

In X-ray radiography it is a common technique to reduce patient absorbed dose by increasing the X-ray tube potential (kVp) while keeping the detector exposure constant by decreasing the tube current-...
David's user avatar
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Depth ionization $\neq$ depth dose for electron beam?

Consider an electron beam which is targeted towards some object with a certain depth. The concept of dose refers to the amount of energy expended by the electrons in collisions with atoms of the ...
In the blind's user avatar
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1 answer
69 views

Energy of electron in photon interactions

There are three ways that a colliding photon can cause an electron to be ejected from the nucleus : via the photoelectric effect, the Compton effect, and pair production. Does the initial kinetic ...
In the blind's user avatar
0 votes
1 answer
25 views

Radiation dose delivered to a cavity of air

I have a cavity of air which is exposed to a radiation source that liberates a known amount of charge in the cavity ( in the form of ionization ). What theory should I use to model the situation so I ...
In the blind's user avatar
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1 answer
38 views

Is the absorbed dose defined as a differential or a quotient?

The absorbed dose D is defined as $D = \frac{dE}{dM}$ You can find this definition in numerious books. However, when looking for calculation examples, the definition $D = \frac{E}{M}$ is used. How ...
Mad's user avatar
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349 views

Conditions for Bragg-Gray Cavity theory

The conditions for applying the theory are, first, that the cavity of material $g$ has to be small enough, so that the cavity does not affect the incoming radiation to the material surrounding the ...
In the blind's user avatar
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0 answers
29 views

Why X-ray imaging base on photon counting is more quick than traditional energy integral detector?

photon counting based on detector can be used to x-ray imaging in industrial pubilc security. In traditional, people often use energy integral scintillation detecor to imaing object through x-ray. The ...
Winston Pan's user avatar
0 votes
1 answer
185 views

What is the input of calculating signal noise ratio (SNR) and detective quantum efficiency (DQE) in estimation of imaging system?

In its definition, the signal noise ratio (SNR) is the ratio of the mean siganl to the standard deviation of the noise. However, for a given picture what is the noise? The detective quantum efficiency ...
Winston Pan's user avatar
0 votes
1 answer
167 views

Is MRI permanent magnet sensitive to temperature?

My question is related to MRI machines that use a permanent magnet to generate their main magnetic field: Are all permanent magnets used in such MRI machines sensitive to temperature, meaning does a ...
Ahmed's user avatar
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2 answers
185 views

Why is it in electrocardiogram (ECG), we talk about the voltage generated by depolarisation of the heart is a vector and not a scalar?

I'm asking to understand is the potential difference generated during depolarisation of the heart an exception to the rule that voltage is a scalar quantity? And if so, why? I remember learning in my ...
Bøbby Leung's user avatar
-1 votes
1 answer
120 views

Does an X-Ray tube have an electric field inside of it? [closed]

I searched the question on the web, but could not a satisfactory answer. Anyway, the question is as follows: The X-Ray tube consists of an anode, which essentially accelerates the electrons, and a ...
Mile Stone's user avatar
5 votes
6 answers
341 views

In radiotherapy, why do normal tissiue or organ cells not die of radiation?

In radiotherapy, why don't normal tissiue cells or organ cells in the way of incoming radiation die, but tumours die instead?
PhysicsEnginering's user avatar
0 votes
3 answers
2k views

Difference between X-ray device and linac

What is the difference between an x-ray device and a linac (for medical purposes)? In case both have to produce photons. Linac: source X-ray device: source As far as I see the major difference is, ...
Ben's user avatar
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0 votes
1 answer
101 views

Difference between an electromagnetic calorimeter and a pet-detector

Is there a conceptual-technical difference between an electromagnetic calorimeter and a pet-detector? Surprisingly I couldn't find a better/rough concept of an Ecal but ultimately it consists of a lot ...
Ben's user avatar
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0 votes
1 answer
241 views

Flow rate of Venturimeter $v=\sqrt{\left(\frac{2\left(P_{1}-P_{2}\right)}{\rho}\right)}\left[\left(\frac{A}{a}\right)^{2}-1\right]^{-\frac{1}{2}}$

How to derive $$v=\sqrt{\left(\frac{2\left(P_{1}-P_{2}\right)}{\rho}\right)}\left[\left(\frac{A}{a}\right)^{2}-1\right]^{-\frac{1}{2}}~?$$ I came across it while studying fluids mechanics in medicine ...
user avatar
1 vote
1 answer
40 views

Scattered radiation factor for diagnostic

I need the confirmation, is it if we put survey meter at 270 degree, does the reading of scattered radiation is same with 90 degree. In my opinion, the reading would be same as the distance is still ...
ash111's user avatar
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2 votes
0 answers
85 views

Dynamic Small Airways Collapse - Understanding the physics of the pressure drop from alveolus to mouth in human lungs

EDIT: I think I have thought of a much better phrasing of my question using the middle diagram below. a) If intrapleural pressure is >0 does airway collapse always occur? b) In a hypothetical ...
hash_define's user avatar
2 votes
2 answers
2k views

Which among alpha, beta and gamma emitters is most dangerous for human body?

Lets say we have three candies: One with alpha emitter in it, one with beta emitter in it and one with gamma emitter in it. All have similar activities. You must eat one, put one in your pocket and ...
QuntumRelativist's user avatar
1 vote
1 answer
79 views

Can photons release electrons? Can neutrons decay into heavier particles?

I'm studying the classification of radiation in 'Radiation Physics for Medical Physicists' by Ervin B. Podgorsak. At some point in the explanation of the two-step process of ionization for indirectly ...
Jorge Gonçalves's user avatar
1 vote
0 answers
44 views

Average geometric efficiency in Positron Emission Tomography

While researching for my thesis I am using the book "Physics in Nuclear Medicine" by Simon R. Cherry, James A. Sorenson and Michael E. Phelps. In Chapter 18.8 they talk about the average ...
Andi's user avatar
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1 vote
1 answer
251 views

Why does MRI (Magnetic Resonance Imaging) have high contrast and spatial resolution albeit having lower frequency and higher wavelength?

So we've been discussing this in the classroom and I really can't say if my answer to this question is correct since there could be various answers to this. I know that to have a high-resolution image,...
user668687's user avatar
1 vote
1 answer
36 views

Can the recoil to the nucleus induced due to radioactive decay be enough to break inter-molecular bonds?

let's say I have radioactive labelled molecule such as ${}^{99m}Tc$--Methyl diphosphonate ${}^{99m}Tc$ undergoes gamma decay and emits a photon of 140 KeV. Said molecule also forms a bond inside bones,...
Tomka's user avatar
  • 411
1 vote
2 answers
192 views

In ultrasound, why doesn't the reflected sound gets reflected again on its way back?

Consider the diagram below illustrating how A-scans work, why doesn't some of the reflected sound on its way back at the red circle interface reflect again (thereby reducing the signal intensity ...
Bøbby Leung's user avatar
0 votes
0 answers
33 views

Why decreases the pressure inside hollow organ, as volume is removed?

I would like to explain in physical terms, why the pressure in the uterus falls, if volume (amniotic fluid) is removed. So far as I understand, p in spheres is inversely proportional to the radius, ...
Meier's user avatar
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1 vote
0 answers
174 views

How do single-pixel cameras work?

To obtain images using a single-pixel camera we need a Digital Micromirror Device (DMD) because single-pixel cameras only possess a single detector (article). From my understanding, a single-pixel ...
user7077252's user avatar
2 votes
0 answers
81 views

What is the physics behind why incorrect cuff size for measuring blood pressure manually or automatically lead to inaccurate results?

The biophysics behind measuring systolic and diastolic blood pressure manually with a cuff and stethoscope is that Determine the approximate pressure it takes for the cuff to occlude the brachial ...
Bøbby Leung's user avatar
1 vote
1 answer
191 views

Why is Polonium-210 more lethal than other radioisotopes? [closed]

So it takes a single microgram or less of pure Polonium-210 to be lethal. Which according to basically all sources makes it the most toxic material or at the very least the most toxic element. But why ...
ShaneC's user avatar
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3 votes
1 answer
96 views

Why is long-term radioactive material so bad?

So i'm currently researching nuclear power and nuclear energy as it is a topic that has always interested me, but when researching nuclear fission waste, and hearing about waste that has a half life ...
Louis Clare's user avatar
1 vote
1 answer
765 views

Bremsstrahlung radiation of a Proton

I often hear Bremsstrahlung being discussed in relation to electrons, for example, x-ray generation. Although I was reading a review on Proton Therapy and when discussing the influence of the various ...
John Tracey's user avatar
1 vote
1 answer
431 views

Energy dependence on bragg peak width

If you look at this plot of proton Bragg peak at different energies. You can see that the Bragg peak shifts right (which makes sense) but also the height and I think the width of the brag peak is ...
John Tracey's user avatar