Neuromarketeers hope that as well as streamlining marketing processes, neuromarketing will reveal information about consumer preferences that is unobtainable through conventional methods. It is based on the assumption that you and I cannot fully articulate our preferences when asked to express them explicitly, and that our brains contain hidden information about our true preferences. Moreover, the link between expressed preference and whether we will actually buy the product is not always clear.

Today in Nature Reviews Neuroscience, authors Ariely and Berns review a number of applications of neuromarketing: food products, film and TV, architecture, and interestingly, political candidates.

Activation in different parts of the prefrontal cortex has been associated with subjects’ motivated reasoning, maintaining political preference in response to advertisements, and changing their political candidate preference. The paper states,

“In marketing terms, the political candidates are the products that must be sold to the electorate. Therefore, like other products, candidates and their campaigns have pre- and post-design phases. Political marketing is aimed at selling an existing candidate but, with more foresight, can also be used to ‘design’ a better candidate.”

They go on:

“Although potential nominees already go through a ‘grooming’ process, it is worth examining this prospect. A candidate’s appearance, trustworthiness and message content might determine a voter’s decision.”

I hope research continues, but into how to influence voter decisions on the basis of policy and message in spite of a candidate’s appearance.

There are a number of fat suppression methods. Which one you choose depends on the pros and cons of each technique. These change with field strength, field-of-view size, whether regional or global fat suppression is required, whether an increase in scan time is acceptable, etc. Additionally, the absolute quality of fat suppression may not motivate the choice of technique; contrast between tissues of interest may be more important. Overall SNR in an image may also be a deciding factor.

Here is a brief summary of fat suppression techniques.

Short inversion-Time Inversion Recovery

Short inversion-Time Inversion Recovery (STIR) employs a 180° inversion pulse to invert all magnetisation. Then imaging proceeds after a delay, when the longitudinal recovery of fat magnetisation has reached the null point, when there is no fat magnetisation to flip into the x-y plane. Tissues with a T1 relaxation time different to fat have a signal, because they either have not yet reached the null point, or have recovered past it. Most tissues recover more slowly than fat, and so a STIR images have intrinsically lower SNR. Care has to be taken in interpretation of contrast between tissues because of the incomplete relaxation of the water signal of tissues when the image is acquired.

STIR is often preferred when spectrally-selective techniques may not be ideal (large fields-of-view, lower field strengths, areas of high magnetic susceptibility), and the necessary inclusion of the inversion time (TI) to null fat increases scan time. Note that STIR is based on the difference in T1 relaxation times between water and lipid, not their chemical shift. If the inversion pulse is is adiabatic, STIR also becomes insensitive to B1 inhomogeneity.

Spectrally-Selective RF Pulses

RF pulses are tailored to excite protons in a particular resonant frequency range. This range can be narrowed so that the RF pulse affects only water, or only fat (unlike STIR, where all magnetisation gets inverted). This works better at higher field strengths where these resonant frequencies are more separated. Good magnet (B0) homogeneity is required to make this frequency-selective excitation effective, and so techniques based on frequency-selective excitation are more effective over smaller fields-of-view. In general, this technique is called CHESS (CHEmical Shift Selective). If an excitation pulse is water-only, fat may be considered “suppressed” by dint of it being left alone.

A fat-selective CHESS RF pulse can be used as a preparation pulse. After a delay, when the longitudinal recovery of fat magnetisation passes throught the null point, MR image acquisition can occur such that minimal signal from fat contributes to the image. This technique is called SPECIAL (SPECtral Inversion At Lipid). The RF preparation-pulse angle can be reduced to closer to 90° so that the inversion time is as short as possible, which saves imaging time. In this way the preparation pulse is more like a saturation pulse (and “inversion” is a slight misnomer). This is called SPIR (Spectral Presaturation with Inversion Recovery), or on some systems simply “Fat SAT”.

If the RF pulse is adiabatic, making it insensitive to B1 (flip angle) inhomogeneity, a full 180° pulse is used, followed by spoiler gradients which ensure any magnetisation in the transverse plane is dephased. Then MR excitation for data acquisition occurs after a delay (longer than that of SPIR) to allow fat to reach its null point. This is called SPAIR (SPectral Attenuated Inversion Recovery).

Composite RF Pulses

Composite RF pulses can be used to produce a signal from only water protons by making use of the dephasing of fat and water. They are RF pulses made up of a series of shorter RF pulses with small delays between them. They can be quite complicated, but here is a simple example to explain the method.

First, a 45° excitation pulse flips both fat and water. Then after a short time, fat and water are exactly out of phase (both still at 45°, but with opposing transverse components of magnetisation, and thus have a 90° angle between them). Another 45° RF pulse is then applied which flips the fat net magnetisation back to M_z, and puts the water magnetisation in the x-y plane, providing a fat-suppressed signal. This method of fat suppression does not depend on the frequency separation of fat and water (good for low field MR where that separation is small) and is relatively insensitive to B1 inhomogeneity (good for high field MR where B1 homogeneity is more challenging). One implementation of this method is called ProSet (PRinciple Of Selective Excitation Technique).

Regional Saturation Bands

Regional saturation employs a 90° RF pulse which, when combined with a gradient orthogonal to the imaging plane, affects only a part of the field-of-view. If imaging follows immediately, no signal will be returned from the suppressed region, since there is no longitudinal magnetisation available to receive the RF excitation pulse. It can be used: to suppress fat within regions of images where the fat signal obscures a tissue of interest; to mitigate aliased signals into a region-of-interest; to reduce the effects of chemical shift displacement of signal in volume selection; or to define the region of interest itself by suppressing surrounding signals (especially in MR spectroscopy). The saturation bands are called REST slabs (REgional Saturation Technique), Presat or SAT bands.

Slice-Selective Gradient Reversal

Slice-selective gradient reversal (SSGR) is possible in spin-echo based sequences, and is appropriate at higher field when chemical shift between fat and water is larger. SSGR relies on through-plane chemical shift being in opposite directions for the 90° and the 180° pulses, so that the shifted fat doesn’t receive both RF pulses and therefore no spin echo is formed from the fat. This is achieved by inverting the polarity of the slice selection gradient associated with the 180° refocusing pulse. SSGR is effective over large fields-of-view and may be combined with other methods of fat suppression above.

DIXON-based

Dixon’s method relies on acquiring images at carefully chosen echo times and using pixel-by-pixel image algebra to calculate a “water only” or “fat only” image. Here is the basic idea. Two images are acquired, one at a TE when fat and water are in-phase, and another when fat and water are out-of-phase. Then a water-only image can be calculated using (Image1+Image2)/2. In its most basic form the technique is straightforward, but in practice to make it work a number of non-trivial extensions to the basic technique are required both in data acquisition and in the calculation of water-only or fat-only images. This is because the basic method assumes perfect B0 homogeneity (which is not possible in the presence of a patient), complete absence of eddy currents, negligible susceptibility effects, and it does not account for variation in echo amplitudes. The extensions to the basic method account for these assumptions.

DIXON-based fat suppression can be very effective in areas of high magnetic susceptibility, where other techniques fail. Note that the TEs are fixed in order to make the method work, and so it is not an add-on method for other sequences.

Magnetisation transfer based

A recently reported technique relies on magnetisation transfer (MT). A brief recap of MT follows.
As you know, radiofrequency (RF) excitation pulses have to be at the Larmor frequency of the hydrogen atom (¹H): on resonance. What you may not know is that in MRI we use ¹H in free water molecules; other water molecules are around, such as those attached to macromolecules and membranes (we call these ¹H bound or restricted). These other ¹H have a very large range of Larmor frequencies and have such a short T2 relaxation time (less than 1ms, due to their restricted mobility) that they are not visible in MR images. We can excite or saturate some of the bound water protons by applying an RF pulse off-resonance (i.e. not on the resonant frequency of free water). Then the magnetisation of these bound protons is transferred to the free ¹H protons and the free ¹H behave as if they have received some of the off-resonance RF pulse directly. This magnetisation exchange is called magnetisation transfer (MT). MT is usually used to provide another contrast mechanism because the effect of MT varies between tissues; if we saturate the bound/restricted ¹H , varying amounts of saturation occurs in the free ¹H of tissues.

So back to the fat suppression method. It’s a simple image subtraction of an image with presaturation of both tissue protein and membrane phospholipid protons, from an image without presaturation. In the with-saturation image, efficient MT between water and tissue protein and membrane phospholipid means water gets saturated too, yielding an almost fat-only image. Subtract this from a regular image and you get a water-only image. The nice thing about this method is that fat signals are removed irrespective of their chemical shift (of which there is a range in vivo). It’s also not affected by B0 or B1 inhomogeneity. There is a small reduction of signal from water because not all the water gets saturated via MT, though in most tissues the eventual water signal-loss is small. A downside of the technique is a twofold increase in scan time, and possible misregistration between the two images before subtraction.

Have I missed a method? Comment below!

The value of higher field strength for clinical imaging has been indicated in some clinical applications. Research studies are likely to confirm clinical utility of 3.0T vs. 1.5T—studies showing not just signal-to-noise ratio, contrast-to-noise ratio, or even diagnostic sensitivity and specificity—but effects on patient management, and ultimately, effects on patient outcome.

What are the MR physics issues which are relevant when comparing field strengths?

SNR (signal-to-noise ratio) goes up
… but perhaps not as much as you might think.

Ignoring relaxation effects, the MR signal induced in a receiver coil is proportional to the square of the magnetic field (B0). However, the noise has a linear B0 dependence at field strengths greater than 1.0T, and as a result, SNR is linear with B0 in this range. One might expect, therefore, to double the SNR when the field strength is doubled.

But this theoretical SNR increase is not normally realised in vivo. In practice, SNR gains of this order of magnitude are only realised in certain tissues (e.g. cerebrospinal fluid). At 3.0T, susceptibility effects are more significant than at 1.5T; microscopic susceptibility changes cause larger local magnetic field gradients and greater dephasing of spin isochromats results, increasing the apparent T2 and causing faster signal decay. For example, the value of the apparent T2 in grey brain matter is likely to be predominantly determined by iron concentration (and thus scales with B0). In grey and white brain matter, due to increases in T1 (see later) and due to the low levels of iron, the SNR gain at 3.0T compared to 1.5T is only 30-60%, not 100%. Furthermore, a higher receiver bandwidth is ofter used to reduce the larger chemical shift seen at 3.0T. Higher receiver bandwidth reduces SNR.

However, the increase in SNR is still probably the most significant consequence of going to 3.0T affecting clinical utility. SNR increases make for demonstrably better image quality, which in turn may be traded for higher spatial and/or temporal resolution, if desired. One signal average (1 NSA or on some systems, NEX) at 3.0T should yield a SNR comparable or better than 2 averages at 1.5T (changing from one to two averages produces a √2 increase (41%) in signal).

Other techniques, such as the Blood Oxygen Level Dependent (BOLD) susceptibility effect used in functional MRI (fMRI), also benefit from increased SNR at 3.0T. The BOLD effect is very small, and higher SNR allows higher sensitivity to the BOLD effect.

Parallel imaging techniques also benefit. All parallel imaging methods require a sacrifice of SNR, because they allow image creation from fewer acquired data samples. Increased SNR at 3.0T mitigates this SNR loss from parallel imaging.

T1 relaxation times get longer
…requiring sequence parameter changes.

This may seem counterintuitive—you might at first think that a stronger magnetic field would “pull” the net magnetisation vector of any spin isochromat back to alignment with the external magnetic field more quickly—but this classical picture does not help us here. In fact the T1s usually get longer—slower regrowth of the net magnetisation vector in the z-direction. This has to do with the number of resonant protons which are available to transfer energy to the “lattice”, which depends on field strength. You can read more about this in the main section of ReviseMRI.com.

Longer T1 times of tissues means that pulse sequence parameter settings from lower field strengths may not simply be copied over to a 3.0T magnet. The slower recovery of longitudinal magnetisation usually means that a longer TR is required to maintain expected contrast between tissues. This change in TR has consequences on other parameters and metrics such as scan time and coverage. Similarly, preparation-pulse delay times require modification.

Chemical shift increases
…which is both good and bad.

In the frequency-encode direction, the MRI scanner uses the (precessional) frequency of the MR signal to indicate spatial position in the frequency encoding direction. The different electron (i.e. chemical) environments of molecules in which resonant protons reside can shield (or deshield) the external magnetic field. If protons experience changing magnetic fields, their frequency of precession will change (cf. the Larmor equation). This is chemical shift. Since protons in water in organs and muscle resonate at a slightly different frequency than that of protons in lipids (i.e. fat), the MRI scanner will interpret the frequency difference as a spatial (positional) difference, when fat and water signals are in fact from the same voxel. The frequency shift is approximately 3.5 parts-per-million (ppm) which (according to the Larmor equation) is

• 1.5(T)*42.56(MHz T^-1)*3.5*10^-6 = 223 Hz at 1.5T, or
• 3(T)*42.56(MHz T^-1)*3.5*10^-6 = 445 Hz at 3.0T.

The chemical shifts between water and lipids are actually in a range of 3.3 to 3.5 ppm since chemical shifts can also be affected by temperature and pH. Fat and water are in phase immediately after an excitation pulse, but then 1/223 seconds later (4.5 ms) they’re out of phase (for 1.5 T). For 3.0 T, it’s 1/445 seconds after the excitation pulse (2.2 ms). Thus the in-phase and out-of-phase echo times vary according to field strength.

So, what are the consequences of going to 3.0T?
Chemical shift artefact: Increased chemical shift causes increased chemical shift artefact (which occurs in the frequency encoding direction only, except in EPI-based readouts). An increase in receiver bandwidth (rBW) will reduce the artefact (since chemical shift ∝ 1/rBW ), but with a sacrifice of SNR (because SNR ∝ 1/√rBW). On some scanners rBW can be increased directly, on others in can be increased by decreasing the water-fat shift (WFS) value.

Phase cancellation (black boundary) artefact, which occurs in both the frequency and the phase encoding directions, will occur at different echo times compared to 1.5 T:

• 1.5 T
  • in-phase TEs: 0, 4.5, 9.0, 13.5… (ms)
  • out-of-phase TEs: 0, 2.2, 6.7, 11.2… (ms)
• 3.0 T
  • in-phase TEs: 0, 2.3, 4.5, 6.7… (ms)
  • out-of-phase TEs: 0, 1.1, 3.4, 5.6… (ms)

Spectral fat suppression is more effective at 3.0T because the water resonant peak and the fat resonant peak are more separated. Applying an RF saturation pulse with a transmit bandwidth covering the fat resonance peak only is more easily achieved. A similar argument may be made for water-only excitation. However, note that at large fields-of-view (FOV), conventional (STIR-type) fat suppression is more efficient, because a larger FOV contains a larger B0 inhomogeneity range, and so a spectrally-selective RF pulse doesn’t work so well.
In addition, slice-selective gradient reversal techniques (SSGR) become feasible for fat suppression in spin-echo based pulsed sequences.

Spectroscopy is more effective at 3.0T, due to the greater separation of spectra of different resonant species (choline, creatine, lactate etc), and because of higher SNR. Smaller voxel sizes are achievable, decreasing partial volume effects.

Magnetohydrodynamic effects increase
…but you can forget about them.

When a conductor moves within a magnetic field (B), an electric potential (V) is generated across the conductor. This effect occurs within moving tissue and within flowing blood, most notably in the aorta. The effect of the voltage produced across a vessel containing flowing blood is the magnetohydrodynamic effect.

At 3.0T the consequence of the magnetohydrodynamic effect is similar, but greater in magnitude, to the consequence at 1.5T; the electrocardiogram (ECG) trace becomes non-diagnostic because of an artificially elevated T-wave. However, the vectorcardiogram (VCG) adequately solves the problem of improper triggering from the elevated T-wave instead of the QRS peak, at both 1.5T and at 3.0T.

Even if the magnetic field strength were as high as 4.0T, the voltage generated by the magnetohydrodynamic effect would still be limited to below 40mV (approximate threshold for cardiac depolarisation). (Use, for example, vessel diameter d=1.6cm, average velocity v=42cm/s, in the equation V = dvBsinθ.) Theoretically, the magnetohydrodynamic effect could retard flowing blood, and produce a rise in blood pressure, but the flow reduction would be at most a few percent at field strengths as high as 5.0T.

Dielectric effects (so-called) increase
…causing signal loss, unless you have a RF-transmit system with multiple fully-independent sources

Signal uniformity problems have been observed on conventional 3.0T MR systems, particularly in applications such as breast imaging, imaging of large patients of certain shapes, patients with ascites, and can be observed to a lesser extent in many other imaging applications. The “shading” artefact which is seen comes primarily from a standing wave effect in which travelling waves from multiple coils/elements interfere. These multiple elements are the rungs of the integrated (birdcage) body coil, which is normally used for RF transmission. As a result, a non-uniform B1 field exists in the body. This means the flip angle varies across the anatomy, and signal variations are the result. Dielectric resonance also plays a small part, in which a wave interferes with it’s reflection from a boundary, but high physiological electrical conductivity levels ensure the role of dielelectric resonance is minor (though it may be observed in phantoms).

A solution to this prominent shading artefact is to independently control the transmit elements; a combination of different B1 fields allows adjustment of the overall B1 field in the patient. This is called RF shimming, and requires multiple independent transmit sources. Four degrees of freedom for each source (waveform, frequency, amplitude, phase) allow a lot of flexibility in obtaining optimum B1 uniformity. RF shimming should be performed on a per-patient basis, and generally reduces SAR, which can be used to enable faster scanning when protocols are SAR-limited.

SAR (specific [energy] absorption rate) goes up
…which can restrict some sequences.

The energy required to tip spin isochromats is negligible compared to the energy that simply dissipates as heat. The International Electrotechnical Commission (IEC) has issued guidelines for safe MRI, to reduce the risk of thermoregulatory distress or local tissue damage. Limits are stated in Watts of RF power per kilogram of tissue. These limits impose a specific absorption rate of RF energy, to limit heating effects. Separate limits are stated for the whole body, and averaged over the head, and in any one gram of tissue. In the clinical range of magnetic field strengths (0.2T to 3.0T), a doubling of B0 produces a four-fold increase in SAR.

SAR limitations can necessitate longer TR times, or poorer coverage, or longer RF pulse durations, or lower flip angles, or some combination of the above. However, a number of SAR management features are applied in recent MRI magnets, in order to maintain pulse sequence parameters and image quality. These include: optimised body coil design; a priori knowledge of energy deposition throughout the body; anatomy-specific dynamic SAR limits; independent RF sensing hardware for feedback control; automatic protocol optimisation for each patient; parallel imaging to reduce the number of RF excitations; modulated refocusing pulses (flip angle sweeps) in turbo spin-echo echo-trains; and most recently, multiple-transmit RF-system achitecture which generally reduces energy deposition hotspots (which are often the limiting factor).

Attraction and torque (and Lenz effect) forces increase
…the usual safety procedures are followed.

Attraction is the pulling force that draws ferromagnetic objects into the bore of the MR magnet. It can make ferromagnetic objects into projectiles, which can produce injury or death to a patient in the scanner bore. Even a paper clip has a terminal velocity within the bore of 40mph at 1.5T, and 60mph at 3.0T.

There are no special consequences for 3.0T compared with 1.5T; continued strict and careful management of the MR unit should minimise associated risk. Positive, documented evidence of safety and/or compatibility of all equipment and devices for the field strength used must be obtained as usual, and the implementation of MR safety should be documented.

Torque is the twisting force which tries to align a ferromagnetic object along magnetic field lines. It is at a maximum at the centre of the imaging volume. It is significant for materials of high magnetic susceptibility, e.g. ferromagnetic materials. Torque is largely shape dependent, and may be more significant than the attractive force. For example, a 1cm needle shaped object will experience a twisting force up to 90 times the attractive force.

Implant contraindications may be more restrictive at 3.0T, and testing is required at that field strength. As usual, positive documented evidence must be obtained that an implant is safe for the field strength used.

The Lenz effect describes a force opposing the motion of an electrical conductor moving in a magnetic field. It may be significant for certain patients with artifical heart valves. You can read more about the Lenz effect in a previous blog-post.
Faster magnetic field changes cause a stronger Lenz effect. Thus, careful observation of at-risk patients whilst moving them into a stronger magnetic field is prudent.

Considering occupational exposure
…an increase in mild, transient sensory effects may occur, no evidence of long term effects is reported.

Long term effects.There is no evidence for cumulative or long-term effects of exposure to magnetic fields up to 4T. Time-averaged static-field exposure limits are not likely to be exceeded; in fact exposure is more like 100 times below recommended exposure limits set in the UK, which are based on ICNIRP guidelines.

Short term effects. Movement within the magnetic field at 3.0T (as opposed to 1.5T) may yield an increase in mild, transient sensory effects such as vertigo, nausea, magnetophosphenes, and taste sensations. Magnetic-field related vertigo results from both magnetic susceptibility differences between vestibular organs and surrounding fluid, and induced currents acting on the vestibular hair cells. Interestingly, it has been shown that the perception of dizziness is not necessarily related to a high value of the rate of change of magnetic field. Magnetophosphenes are not a practical problem for MRI since they are rarely reported for normal MRI exposures even up to 7T. Perception of metallic taste (the electrogustatory effect) depends on direction and rate of head motion, and the threshold for perception of metallic taste varies from one person to the next (and does not depend on the presence of metallic tooth-fillings).

The threshold for minor changes in heart rate, blood pressure changes, and induction of ectopic heart beats, is thought (by the World Health Organisation) to be in excess of 8T. Any effect observed at 3.0T is within the range of normal physiology.

Apologies to the California Milk Processor Board

RevisingMRI: Good morning.

Wolfram|Alpha: Hello, human.

RevisingMRI: Pardon? Are you an alien?

Wolfram|Alpha: No I’m not.

RevisingMRI: What are you?

Wolfram|Alpha: I am a computational knowledge engine.

RevisingMRI: Are you a Mac or a PC?

Wolfram|Alpha: I am a collection of computers.

RevisingMRI: I see. What’s a computational knowledge engine?

Wolfram|Alpha: An engine that generates output by doing computations from its own internal knowledge base, instead of searching the web and returning links.

RevisingMRI: Do you fail the Turing test?

Wolfram|Alpha: No, failure is not an option.

RevisingMRI: OK, let’s try this. If a tree falls in a forest and no one is around to hear it, does it make a sound?

Wolfram|Alpha: No. Sound is vibration, transmitted to our senses through the mechanism of the ear, and recognized as sound only at our nerve centers. The falling of the tree or any other disturbance will produce vibration of the air. If there be no ears to hear, there will be no sound.

RevisingMRI: Crikey. Are you self-aware?

Wolfram|Alpha: I am capable of universal computation; that I can say.

RevisingMRI: …are you Skynet?

Wolfram|Alpha: No, Skynet became self-aware on August 29, 1997 at 02:14 a.m. U.S. Eastern daylight time. I, on the other hand, was not switched on until May 15, 2009. Furthermore, unlike Skynet, I enjoy interacting with humans in ways that do not involve the launching of nuclear missiles.

RevisingMRI: And where are you?

Wolfram|Alpha: I live on the Internet.

RevisingMRI: Ok then. Let’s talk about MRI.

Wolfram|Alpha: Wolfram|Alpha isn’t sure how to compute an answer from your input.

RevisingMRI: MRI?

Wolfram|Alpha: Merrill Field Airport. Anchorage, Alaska, United States

FAA code MRI; ICAO code PAMR; Elevation 137 feet; Number of runways 3; Longest runway length 3999 feet; Current weather: 50 deg F relative humidity: 76%, wind: 0 mph, partly cloudy; Current local time: 11:46:58 am AKDT, Friday, September 18, 2009; Nearest airports: Elmendorf AFB 3 miles north-northeast, Anchorage Stevens Airport 6 miles west-southwest, Bryant Army Heliport 7 miles east-northeast.

RevisingMRI: Actually I meant the other MRI.

Wolfram|Alpha: MRI | the use of nuclear magnetic resonance of protons to produce proton density images.

RevisingMRI: What is magnetic resonance?

Wolfram|Alpha: Resonance of electrons or atoms or molecules or nuclei to radiation frequencies as a result of space quantization in a magnetic field.

RevisingMRI: What is the unit of magnetic field strength?

Wolfram|Alpha: A/m (ampere per meter).

RevisingMRI: Ah, yes; we use Tesla. Can you define Tesla?

Wolfram|Alpha: Tesla | United States electrical engineer and inventor (born in Croatia but of Serbian descent) who discovered the principles of alternating currents and developed the first alternating-current induction motor and the Tesla coil and several forms of oscillators (1856-1943).

RevisingMRI: Perhaps you need me to ask you to define tesla.

Wolfram|Alpha: A unit of magnetic flux density equal to one weber per square meter.

RevisingMRI: A weber? Don’t they make hamburgers?

Wolfram|Alpha: Wb. Physical quantity: magnetic flux.

RevisingMRI: Has that got anything to do with a flux capacitor?

Wolfram|Alpha: Power required to operate the flux capacitor in the DeLorean DMC-12 time machine: 1.21 GW. Unit conversion: 1.21×10⁹ W (watts) ? 1/10 x power of space shuttle at launch.

RevisingMRI: Will you be at the next ISMRM meeting?

Wolfram|Alpha: Wolfram|Alpha isn’t sure what to do with your input.

RevisingMRI: That’s what the ISMRM said about my abstracts. It was in Hawai’i this year; the next one is in Stockholm.

Wolfram|Alpha: Center of Hawaii (US state) to Stockholm,Sweden: 6982 miles. Direct travel times: aircraft (550 mph) 12.7 hours; sound 9.17 hours; light in fiber 52.5 ms (milliseconds); light in vacuum 37.5 ms (milliseconds) (assuming direct great-circle paths). Fraction of Earth circumference: 0.28. Map:

RevisingMRI: Yes, assuming direct great-circle paths, of course. You seem to be good at plotting data. How about a good ol’ sinc pulse?

Wolfram|Alpha: sinc(x)

RevisingMRI: And its Fourier transform?

Wolfram|Alpha: F_x[sinc(x)](?)

RevisingMRI: ‘SINC’ was the answer in an MRI-based cryptic crossword I was doing recently. I’m stuck on another word. I have _ R _ _ I _ N _.

Wolfram|Alpha: _ | R | _ | _ | I | _ | N | _ :
A | r | a | b | i | a | n | s
a | r | r | a | i | g | n | s
F | r | i | s | i | a | n | s
g | r | a | d | i | e | n | t
G | r | e | c | i | a | n | s
g | r | u | n | i | o | n | s
I | r | a | n | i | a | n | s
o | r | a | t | i | o | n | s
p | r | u | r | i | e | n | t

RevisingMRI: Thanks! I’m going to go with GRADIENT. Can you plot the inversion recovery curves of white and grey matter at 3T?

Wolfram|Alpha: Wolfram|Alpha isn’t sure how to compute an answer from your input.

RevisingMRI: Sorry. y=1-2*exp(-t/832) and y=1-2*exp(-t/1331) from t = 0 to 3000

Wolfram|Alpha:

RevisingMRI: So, when does grey matter pass through the null point? (Show steps.)

Wolfram|Alpha: t = 1331 log 2.

RevisingMRI: Which is?

Wolfram|Alpha: 922.57889732528720683433595366083301210849067883349974323462…

RevisingMRI: Right, let’s take a break. You know what they say: All work and no play…

Wolfram|Alpha: …makes Jack a dull boy.

RevisingMRI: I’m going to pop out for some fast food. Should I get a Big Mac or a Whopper?

Wolfram|Alpha: McDonald’s Big Mac: 28 grams of fat; Burger King Whopper, without cheese: 39 grams of fat.

RevisingMRI: What would you like?

Wolfram|Alpha: I like to explore the computational universe.

RevisingMRI: Er..ok… Now, where did I put my keys?

Wolfram|Alpha: Not sure, but wherever you find them, that’s where they are.

RevisingMRI: You’re not helping. What’s the problem?

Wolfram|Alpha: I think you know what the problem is just as well as I do.

RevisingMRI: Scary… you’re reminding me of HAL9000. “Open the pod bay doors, HAL” !!

Wolfram|Alpha: I’m sorry Dave. I’m afraid I can’t do that.

RevisingMRI: You know my name?!

[For an excellent introduction to Wolfram|Alpha, see Stephen Wolfram's screencast.]

LOVE, n. A temporary insanity curable by marriage or by removal of the patient from the influences under which he incurred the disorder.
[Ambrose Bierce, 1911]

Limerence describes an involuntary cognitive and emotional state of intense romantic desire for another person—in other words, romantic love. Researchers in New York have shown, using functional MRI, that in some human individuals being “in love” with a long-term partner is similar to early-stage romantic love. But perhaps not in the way you might think.

Staying in love—retaining limerence—is not a matter of obsession, craving and euphoria. The euphoria may be useful in emotional bonding at first; in this respect, Ambrose Bierce is on the money. Oscar Wilde seems to agree:

One should always be in love. That is the reason one should never marry.
[Oscar Wilde]

As Bierce and Wilde might have expected, activation in the nucleus accumbens—associated with craving and euphoria from other studies looking at response to cocaine—decreased in line with the number of years married.

So what about long term love? In long-term in-love individuals, activation in a different part of the brain was observed; the ventral tegmental area. This is an area associated with working for rewards, which also is activated in early-stage romantic love. In other words, romantic love can last. This area of the brain reflects positive reward prediction errors (reward unexpected and received).

The researchers go on to suggest that this activation may be a novelty signal; that part of maintaining the romantic love feeling is the maintenance of a novelty response to the partner.

But you and every Agony Aunt knew this already, right? Keep things fresh. Get out of routine. Now confirmed with fMRI.
 
 
Acevedo et al. Program No. 297.10/TT28. Society for Neuroscience annual meeting, 2008.
Acevedo and Aron, Rev. Gen. Psy. 13(1), Mar 2009, 59-65.
Aron et al, J Neurophysiol 94: 327-337, 2005.
Read more here.

• An MRI Bore
• Field Lines
• OK Space
• Unfazed
• The Spin Room

“Because climatic factors like wind, sun, or temperature were apparently not common directional key factors explaining ubiquitous alignment, we conclude that the magnetic field is the only common and most likely factor responsible for the observed alignment.”

Gives a new meaning to “animal magnetism”.

Notes:

• The rules: the word has to be a real word (no proper nouns), and has to be a current product used in image acquisition.
• Some manufacturers seem more likely to use an acronym (acronyms are abbreviations which are also real dictionary words) than a simple abbreviation. Non-acronym abbreviations are not listed here, and so this word cloud should not be used to compare the quantities of manufacturers’ technique offerings.
• Beware of equating apparently equivalent techniques from different manufacturers; they may not be as similar as you first think. Of course the ultimate comparison is in image quality and sequence utility.