# What is ct: Definition and 58 Discussions

Czech Television (Czech: Česká televize [ˈtʃɛskaː ˈtɛlɛvɪzɛ]; abbreviation: ČT) is a public television broadcaster in the Czech Republic, broadcasting seven channels. Established after the Velvet Revolution in 1992, it is the successor to Czechoslovak Television founded in 1953.

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1. ### Does Radiation from X-Rays/CT Stay in Body Forever (Risks)?

I'm slightly confused by what medical professionals/scientists say when they say to limit exposure to x-rays/CT/PET, etc. scans if possible, due to radiation. I'm also confused as to why we're often told to leave the room when a relative is getting such a scan, given that medical staff that...
2. ### Why is time = ct and not t in special relativty?

Why is time = ct and not t in special relativity? I just started reading the book I was recommended. Maybe I missed it but as stated in the title why is time = ct and not t in special relativity? I understand they want distance/space = time. Just how do they go about doing that mathematically...
3. ### Best CT connected energy meter rating for a CT with secondary 5A

I work in a Maldivian Utility Company. Our engineering team is pretty weak so I don't have anybody in the company to ask even though this is the state electric company. A supplier quoted us 2 CT meters . Rating for one is given as 1A(6A) and other as 5A(20A) which I believe is 1A basic current...
4. ### B Shankar on Lorentz Transformation: Does x' = ct'?

On the Yale University Prof Shankar Youtube vid 'Lorentz Transformation' Prof Shankar writes up on the board that x = ct and then x prime = c t prime. It is the basis of all that follows. But i don't understand. at x = 0, t = 0 and x prime = 0 and t prime = 0. He's got that written up...
5. ### Voltage measurement on a Current Transformer (CT)

I don’t know the ratio of the CT. I’m just looking for an explanation on this. I thought in order to measure output voltage you need to pass the current through a resistor and read the voltage drop. A co worker put 400a through the CT and measured 130v. Something just seems off to me. Can you...
6. ### Cancer Risk and CT Scans: Understanding the Findings of a Data Linkage Study

Hello, I don't have a background in medical research, but I was interested in understanding the conclusions of this paper: Cancer risk in 680 000 people exposed to computed tomography scans in childhood or adolescence: data linkage study of 11 million Australians I'm not understanding a few...
7. ### CT Scan image reconstruction (80 KeV vs 80 kVp)

Hello everyone, I was wondering what would be the differences in case that we had to reconstruct a set of 80 kvp images vs a set of 80 kev images. I suppose that it would be faster in the first case since there would be less time needed since the attenuation coefficient would be fixed in the...
8. ### 256 slice CT scan x-ray tube beam silent quiet

Just has my first CT scan ever for low dose cardiac scoring. Held my breath twice with gantry in fixed position and then once again with gantry spinning. I thought I would have heard the high pitched x-ray when beam energized but didn't at all. All I heard was normal fans and the mechanicals of...
9. ### CT Scan to editable Solidworks file?

Hello, I have CT scanned an object at my local hospital, and I want to convert the object to an editable part in SolidWorks. So far, I've used the program 3D Slicer to create a label map of the object and exported it to an .STL format. However, it doesn't seem to be editable at all when I...
10. ### Design of CT with ferrite core for reverse operation of CT

I have to couple noise into data cable(cat5) in common mode. I have done this with a CT of 50A/1A, ferrite core. What I have done is, I connected the S1 and S2 of CT to probe of my signal generator and inserted the cable through the whole of CT(ring type). I got maximum of 380mV in the cable...
11. ### Different voltage measure while probe connected to 50/5A CT

I have connected the probe to secondary of ring type CT and placed a wire as primary with one multi-meter connected at both ends. When I am checking the probe ends, its 7.1V AC, but it reading 45mV AC when connected to CT. Why this is happening?
12. ### Is it possible to see Newton rings in CT (xray) images?

I have seen what looks like Newtons rings interference pattern in transverse CT images of 2 solid water block on top of each other. My understanding is that Newtons rings occur in visible light eg photography or scanners. Can anyone shed some light on this? :)
13. ### Single CT (600/5A) to infeed PLC Analog card+Amp analog meter

Hello, i have Current Transformer 600/5A, it connected with Amps Analog meter (0-600A @class2.5). i want to update without remove connection of old analog meter and update PLC analog input card +signal convertor 0-4mA, my doubt is will take connection for both (measuring device) at same point...
14. ### Signal to noise ratio in a CT scanner

Homework Statement If the relative noise (noise divided by signal) in a region of a CT slice is measured to be N what would be the value if the tube current was halved, the pitch increased from 0.9 to 1.2, the rotation time increased from 0.75s to 1s and the slice width increased from 1mm to...
15. ### When does a CT give better information than an MRI

In both cases there are contrast agents available. MRI has vastly superior location error but that doesn't mean everything. It also doesn't illuminate the tissue in the same way as x-ray optics. With MRI you can find where molecules are but wouldn't necessarily illuminate an equivalent density...
16. ### What is the Rh = ct cosmology?

I have been looking at several articles recently about the Rh = ct cosmology, but none of them have explained the meaning of the equation. They just assume than anyone looking at such an article will already know what it means. I guess that (1) h is the Hubble "constant", and (2) c is the...
17. ### Medical MRI vs. CT: Which Scan is Better?

Hello guys, I have few questions 1. I know MRI is best for soft tissue masses? What does soft tissues mean? I searched on the internet and the definition is vague. Is it simply all the tissue apart from bone in the body, which means its includes organs such as liver. Or is it all supporting...
18. ### Do wave functions go to zero at ~ct?

Suppose you have a free election and you make a measurement of its position r_0 at time t = 0. You then wait some time t required for the wave function to evolve out of its collapsed eigenstate. The electron now supposedly has a wave function expanding to infinity in all directions, albeit with...
19. ### What does f(x,y) in the 2D CT image account for?

What does f(x,y) in the 2D CT image account for? If for density, then which material is considered as a reference for that density? If for atomic number, then again which is the reference substance?
20. ### What Should Be the CT Turns Ratio for a 30MVA Transformer in a Railway Network?

Hi, A 132kV to 50kV single phase 30MVA transformer supplies an electric railway network. It is to be protected with differential protection using an electronic protection relay that accepts 1A CT inputs. If the CTs are to be continuously rated for a 40MVA load what would be the ideal turns...
21. ### Medical Is MRI a Better Option for Detecting Muscle Damage Compared to CT Scan?

In the case of detecting muscle damage, would there be any reason to choose a CT scan over MRI? I know MRI takes longer and can be more expensive, but the CT scan radiation seems to be high enough to try and avoid it if possible. fyi, I am in communication with a doctor, but he's taking ages to...
22. ### News Professor claims Newton Ct massacre a hoax

This one is a DOOZY! A professor at Florida Atlantic University claims that no one was killed at Sandy Hook Elementary school, "that trained “crisis actors” may have been employed by the Obama administration to shape public opinion on gun control."...
23. ### Green Liquid Leaked from CT Secondary Terminal Board of 132 kV GIS

Hye everyone! An unknown thick-and-sticky green liquid was found leaked from 2 out of 9 feeders, of our 132 kV Switchgear. The liquid was leaked through the cable gland that connected to the Secondary Terminal Board insulating cap of the Current Transformer, at the GIS. I had done: 1)...
24. ### Spacetime diagrams: ct axis and time contraction and length dilation

Hi, this isn't really a homework problem... but I'm just wondering I see the time axis as c*t, now people say that its to scale the time axis so that the world line of light is 45 degrees. But if you were to multiply time by the speed of light, wouldn't you just get the units metres or...
25. ### How does backprojection of CT scanners cause star blur

Homework Statement In the context of image reconstruction using backprojection by CT scanners - Why / how does backprojection cause star blur? Homework Equations Figure 13 of http://depts.washington.edu/nucmed/IRL/pet_intro/intro_src/section4.html and Figure 25-16 of...
26. ### Equation z = ct + d, z is measured in meters and t in seconds; dimensions of D?

Homework Statement In the equation z = ct + d, z is measured in meters and t is measured in seconds. What are the dimensions (units) of d? answer options are... s/m, m/s, m, s, m*sHomework Equations The Attempt at a Solution plugged in m for z, s for t, and m/s for c. solved for D and got 0.
27. ### What causes the streaks in a CT scan when a metal object is present?

What exactly causes it when a metal object is placed near the scanner?
28. ### How many turns on a 50:5 CT for proper current ratio?

Trying to resurrect an old, combination, analog volt/watt/amp meter. Traced the problem to a bad 50:5 current transformer (nothing coming out of the secondary taps with a 15 amp load going through the primary donut hole). I want to make sure there are no other problems with this unit before...
29. ### The CT complex exponential is NOT periodic

I'm taking a signals and systems class and the textbook (Signals and systems by Oppenheim) says the CT complex exponential of the form x(t) = C eat with C and a complex is a periodic signal. I fail to see how. Let C = |C| ejα (exponential form of a complex number) and a = r + jω (rectangular...
30. ### Why does CT utilise compton scattering?

why does conventional xray imaging utilise photoelectric effect but ct utilise compton scattering? i know that at different energies, different mechanisms (eg compton scattering, photoeletric effect, pair production) dominate but do they not chose the energy beam to correspond the process that...
31. ### Solving For t in A Sin(Bt) - Ct + D = 0

Hello, I have an equation which I am trying to solve for t. Of course the problem I'm having is due to the combination of ts within the argument of the sin term and also outside of it. I think I could also manage without the constant D (using sin(x)/x=sinc(x)), but that's no help here (as...
32. ### Characterizing a CT via a major B-H loop?

I contend this cannot be done! A popular method of modeling non-linear cores is to obtain the values for remnant flux density, saturation flux density, and the coercive force at some major hysteresis curve, and to then mathematically extrapolate a curve (a few other parameters are also needed...
33. ### Show whether this sequence conv or div by CT?

Homework Statement Show whether the series 1/sqrt(n^2 + n) converges or diverges by using the Comparison Test.Homework Equations The Attempt at a Solution It's clearly less than 1/n (divergent) which doesn't help and it's greater than 1/n^2 (convergent) [at least for large n] which doesn't...
34. ### Internships for Applied Physics Majors in CT?

My school has a neat internship program where they will pay a stipend for the summer if you can find an "internship" somewhere related to your career goals. The nice thing is that it doesn't even have to be a real internship--all that you need is some place willing to let you work for them...
35. ### Understanding the Derivative of F=Fi (sin ct)

Homework Statement differentiate F=Fi (sin ct) The Attempt at a Solution Fi is a constant = Fi (-cos ct)(c) That is the solution I keep getting, but my buddy keeps getting Fi (- cost ct)/c in other words, he thinks - cost ct should be divided by c, anyone care to...
36. ### Transformers core total load in VA on the CT secondary

Homework Statement A current transformer has a primary winding of two turns and a secondary winding of 100 turns. The secondary winding is connected to a ammeter with a resistance of 0.25 ohms. the resistance of the secondary of the current transformer is 0.75 ohms. The value of current in...
37. ### Medical What is Physical Principle for CT ?

Hello How are u ? please help me What is Physical Principle for CT ( Computed Tomography ) ?
38. ### CT for restricted earth fault (REF) protection

Does somebody could advice me, whether the nominal primary CT to be used for REF protection must be same? The CT I have now as follow: Power Transformer: 60MVA, 150/20kV, Ynyn(0)d1 CT on 20kV switchgear 2000/5, class 5P20 CT on neutral Power Transformer: 1200/5, class X Relay to be used...
39. ### How Do You Calculate Equivalent Capacitance and Charge in a Complex Circuit?

Homework Statement Find the equivalent capacitance of the capacitor combination, Ct and the charge over C5:Q5 Vab=10V C1=3uF C2=11uF C3=12uF C4=6uF C5=9uF Homework Equations 1) 1/Ct=1/C1+1/C4 = 2uF 2) 1/Ct= 1/C2+1/C5 = 99/20uF Parallel: 2+99/20+12=379/20uF Ct=379/20 uF...
40. ### Can Conformal Transformations Explain Torsion in Different Spacetimes?

CTs are not a change of coordinates but an actual change of the geometry, right? In principle, we can change the Minkowski spacetime into Riemannian one even Riemann-Cartan one by some kind of CT. In the Riemann-Cartan spacetime there is torsion while it is torsion-free for Minkowski spacetime...
41. ### Linear algebra proof with operator T^2 = cT

Homework Statement Let T:V--->V be an operator satisfying T^2=cT c=/=0. Show that V=U\opluskerT U={u l T(u)=cu}Homework Equations The Attempt at a Solution Now before I start, just one quick question about ker T: U seems to be an eigenspace since T(u)=cu with c the eigenvalue. But that must...
42. ### Medical X-ray, CT scan, Ultrasound, MRI detecting blanks ?

This is for a sci-fi novel I’m writing, and I actually posted this at another site but the answers given were a little vague. What would occur, either on a computer monitor (or other monitoring device, depending on the machine) or on a photo film, if an: a. X-ray b. CT scan c. ultrasound...
43. ### Mechanical engineering - Cam Laws - Ct Accel.

1. Homework Statement If you could please tell me the "fall" laws for displacement, velocity and acceleration for a cam with constant acceleration. 3. The Attempt at a Solution Could only manage to find the laws for the rising part, in a 1996 book. Didnt find the laws on google...
44. ### Mechanical engineering - Cam Laws - Ct Accel.

Homework Statement If you could please tell me the "fall" laws for displacement, velocity and acceleration for a cam with constant acceleration. Homework Equations The Attempt at a Solution Could only manage to find the laws for the rising part, in a 1996 book. Didnt find...
45. ### Understanding CT and VT Saturation Effects

Can anyone explain why a CT would be subject to flux saturation, but a VT normally wouldn't?
46. ### Why is ct used as the fourth dimension in Special Relativity?

I'm looking for an explanation as to why a lot of results of Special Relativity are described using ct as a fourth dimension instead of just t. Now, I understand that using ct in a Minkowski diagram with identically scaled axes will cause worldlines of light to angle at a nice 45 degrees, and...
47. ### What is the correct understanding of the ct dimension?

I'm confused about how to understand the ct dimension. I cannot get passed thinking that physically real dimensions mean more degrees of motion. If a flatlander went to the store to buy a can of Coke, the closed container would be a circle. The container is closed simply because there...
48. ### Medical Another CT dose related question

Sorry for having to ask another question, but there is just one more thing that I want to get my head around. Let's say you have this protocol: Standard Resolution 64/40 x 0.625 collimation 2.5mm thickness 40/25 mm increment 240 scan angle 0.4s rotation 120 kv 55-165 mas 512...
49. ### Medical CT Dose Info: Understanding CTDI & DLP Values

I've recently started a mini project on typical doses that patients receive when having particular CT examinations and there is just something that I don't really understand that I was hoping someone here might be able to help out with. Now when a doctor takes some CT images the CT machine...
50. ### Understanding ct: Time vs Distance on Spacetime Diagrams

ct axis?? Now that I am looking at spacetime diagrams that involve the speed of light, I am seeing the vertical axis as "ct". Since "c" is meters/second and "t" is seconds then wouldn't ct be ((meters/seconds)*seconds) and end up being METERS? Why would the time axis be in meters? I would...