X-ray Hardware: An Overview for Clinicians Richard G. Spencer, M.D., Ph.D. Atomic Magnetic Resonance Unit National Institute on Aging, National Institutes of Health Baltimore, Maryland USASlide 2
Why go to a discussion? ii) to give smart responses i) to ask great inquiriesSlide 3
1. Magnet 2. Angles 3. Transmitter 4. Collector 5. Test • Considerations • Reasonable inquiries • A couple points of interest • A couple of detailsSlide 4
Magnet Considerations • High field for high flag to-commotion proportion • Weight • Diameter and length (understanding background; field homogeneity) • Homogeneity (spatial); Field security (transient) • Configuration (get to; patient experience) • Cryogenic effectiveness (working expenses)Slide 6
What kind of magnet is it? Is it protected? Field quality? Bore measure? How steady is the field? What\'s the field homogeneity?Slide 7
Resistive Magnet Type Wire Solenoid • Field solidness require an extremely stable 10\'s of kW power supply • Power prerequisites B 2 cooling necessities 0.2 T or lessSlide 8
Permanent Magnet Type • Excellent field security • Configuration: open frameworks are accessible • No power utilization be that as it may... • Weight- - can be tremendous: press 0.2 T entire body weighs around 25 tons • 0.2 T neodymium compound ~ 5 tons • Homogeneity- - can be an issueSlide 9
Open Permanent Magnet System Siemens Viva- - 0.2 TSlide 10
Superconducting Magnet Type • Required for high field frameworks • Homogeneous field • Stable field notwithstanding... • Expensive • Quench wonder Siemens/Bruker Magnetom Allegra-3T, head justSlide 11
Field Strength • Polarization of nuclear cores Larger field More turn arrangement More motion from every pixel or voxelSlide 12
Trading Rules Signal-to-clamor expanded at high field Resolution SpeedSlide 13
More flag from every pixel implies: Each pixel can be littlerSlide 14
More flag per unit time implies: Images can be gained speedier Cardiac MRI Functional MRI RN Berk, UCSD S Smith, OxfordSlide 15
• Greater phantom determination Field Strength in Spectroscopy 31 P NMR Spectrum of Skeletal Muscle at 1.9 T 31 P NMR Spectrum of Rat Heart at 9.4 T Baseline uncertain Baseline determined PCr - ATP - ATPSlide 16
Field Strength Considerations However, at higher field: • expanded synthetic move curios, e.g. fat/water • expanded vulnerability artifacts • expanded siting cost • expanded introductory costSlide 17
Field Strength Ohio State, Bruker 8T Whole-body System Gradient-reverberate Images Typical clinical frameworks: 0.2 T to 1.5 T to 3 T Whole-body: 3 T, 4 T, … , 8 T, 9.4 T accessibleSlide 18
Field Strength High field particularly helpful for fMRI and spectroscopy- - less clearly so for standard imaging • Typical creature frameworks: 4.7 T, 7 T,… , 9.4 T, 11 T even 9.4 T, 11 T verticalSlide 19
Bore Size 600 mm magnet warm bore 570 mm magnet at shoulder incl. shim 360 mm angle loop inward breadth 265 mm RF-headcoil internal measurement Siemens/Bruker Magnetom Allegra-3T, head just • Bigger is better- - e.g. "head just" fits just heads!Slide 20
Bore Size • Human i) Whole Body (run of the mill: 100 cm) ii) Head just (run of the mill: 80 cm) •Animal 15 cm, 20 cm, 30 cm, 40 cm, ... In any case: • Larger bore larger periphery field • Larger slope sets can be slower • CostSlide 21
Magnetic Shielding: Containment of the Fringe Field • Fringe field: part of the attractive field that reaches out past the magnet bore • 5 G taken as most extreme safe open presentation • Effect on e.g. pacemakers, steel instruments, and attractive cards • Effect from e.g. moving autos and liftsSlide 22
Magnetic Shielding Considerations • Weight • Footprint • Expense including space Note: periphery field is 3DSlide 23
Magnetic Shielding Options • Unshielded: • Lightest, least expensive However: biggest field impression, most costly space • Passive protecting: ferromagnetic material put outside magnet • Small field impression: diminish by calculate of 2 all bearings However: heaviest- - 10\'s of huge amounts of iron • Active protecting: electromagnetic counter-windings outside the primary magnet curl • Similar field impression concerning uninvolved protecting • Mild increment in weight versus unshielded However: most noteworthy magnet costSlide 24
Sample Magnet Specifications • Field solidness: superior to 0.1 ppm/hour float Note: fat-water division = 3.5 ppm • Field homogeneity*: superior to 0.3 ppm more than 22 cm and 5 ppm more than 50 cm breadth circular volume (DSV) *without room-temperature shims 1 ppm = 0.00001%Slide 25
Magnetic Field Gradients: required along every one of the three tomahawks Coils Magnetic Field—changes with position Field Strength I Distance I (flow) heading demonstrated bySlide 27
Operation of Gradients No angle: B z,Local = B 0 z With slope: B z,Local = B 0 + z G z Spatial variety of the B field grants spatial mapping of twists: recurrence spatial positionSlide 28
Gradient Considerations • Want high in-plane determination • Want contract cut ability in 2D imaging • Want pictures which aren\'t misshaped • Want to have the capacity to picture rapidlySlide 29
What\'s the inclination linearity? What\'s the slope quality? What\'s the ascent time of the inclinations? Are the slopes effectively protected?Slide 30
Two Different "Bandwidths" in MRI • Excitation Bandwidth of a radiofrequency heartbeat The beat energizes turns in this scope of frequencies • Receiver Bandwidth The recipient can identify motions in this scope of frequenciesSlide 31
Sampling amid MRI flag obtaining Excitation BW resound flag 90 180 rf G s G PE Detection BW G read ADC Sampling time, tSlide 32
Excitation Bandwidth and Gradient StrengthSlide 33
Excitation beat Frequency band energized Excitation Bandwidth Fourier rf adequacy BW Short heartbeat: Broad band (kilohertz) t (milliseconds) BW Long heartbeat: Narrow band Fourier rf abundancy t (milliseconds) (kilohertz)Slide 34
Pulse Bandwidth a.k.a. Excitation Bandwidth Longer span beats • smaller excitation transfer speed be that as it may… • longer resound time—loss of flag from short T 2 species • more prominent specimen warming • unwinding impacts amid heartbeats Would get a kick out of the chance to have the capacity to utilize short heartbeats and still have limit cutSlide 35
Slice inclination quality + Pulse data transmission Slice thickness G s z = BW excitation (Hz) 2 G/cm = 20 mT/meter Frequency G 0.5 G/cm 2000 Hz Pulse Bandwidth Spatial measurement 2.5 mm Slice Thickness 1 cm Slice ThicknessSlide 36
Effect of Slice Gradient Strength on Slice Thickness Slice ThicknessSlide 37
Receiver Bandwidth and Gradient StrengthSlide 38
MRI maps a recurrence range to a spatial range G r FOV = BW recipient (Hz) Receiver BW=4,300 Hz Receiver BW=4,300 Hz G r = 2 Gauss/cm G r = 0.5 Gauss/cm G FOV = 2 cm FOV = 5 mmSlide 39
Effect of Read Gradient Strength on In-plane ResolutionSlide 40
B sought B incited Gradient Eddy Currents Faraday\'s Law Increased streams with more quick exchangingSlide 41
B actuated causes B-field twists Gradient intensifier driving waveform Resulting angle waveform Cure #1: Pre-accentuation Gradient enhancer driving waveform Resulting slope waveformSlide 42
Cure #2: Shielded Gradients Gradient Coils Magnet bore Gradient Shield CoilsSlide 43
Gradient Linearity Effect on Image Accuracy B z, Local = B 0 + G (z) Nonlinear angle: geometric bending Linear angle: nondistorted picture B z, Local = B 0 + z G z straight zSlide 44
Sample Gradient Specifications • Gradient quality: 2.5 G/cm (clinical) 4 G/cm, 8 G/cm 10-100 G/cm (creature) Increased inclination quality higher determination, smaller cuts in any case: likewise expanded warming, expanded ascent time (slower) • Gradient exchanging time (rise and fall time) relies on inductance and driving voltage: 0.2 ms to ascend to 2 G/cm Faster exchanging better execution in quick imaging arrangements • Gradient linearity: 5% more than 22 cm width round volume Better linearity less picture contortionSlide 46
Transmitter Considerations • Need to consistently energize extensive data transmission • Require precise molded heartbeats (time, abundancy) • Desire simple to control yield • Frequency steadinessSlide 47
What\'s the transmitter control? What\'s the linearity of the speaker?Slide 48
Transmitter Low power rf Transmitter Linearity Input 1 volt Gain set to two Output 2 volts Low power rf Transmitter Gain set to two Input 2 volts Linear: Output 4 volts Nonlinear: Output = 3.5 voltsSlide 49
Transmitter linearity is critical for precise molded heartbeats Transmitter Low power contribution to transmitter speaker High power yield from transmitter intensifier ...and for aligning heartbeatsSlide 50
What is a decibel? The dB scale communicates enhancement or constriction as the logarithm of a proportion: dB = 20 log 10 (A 2/A 1 ) A 2/A 1 dB 2 6 10 20 100 40Slide 51
Sample Transmitter Specifications • Maximum yield: 15 kW • Linear to inside 1 dB over a scope of 40 dB • Output security of 0.1 dB more than 10 ms beat • Output dependability of 0.1 dB heartbeat to-heartbeatSlide 53
Receiver Considerations Goal: Receive the microvolt NMR flag and change over it to a discernible resound/FID • Without debasement by commotion • With devoted sufficiency propagation • With loyal recurrence generationSlide 54
What\'s the digitizer determination? What\'s the beneficiary data transfer capacity? .:
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