____________ or __________ produces replications of moving anatomy across the image in the phase encoding direction.

225

As ___________  only occurs during the phase axis, the direction of phase encoding can be changed, so that the artefact does not interfere with the area of interest.

227

______________ nulls signal from specified areas. Placing            "        "           volumes over the area producing artefact nullifies signal and reduces the artefact.

228

 When imaging the chest and abdomen, a method known as ______________ or ____________ can greatly reduce ghosting from respiration.

230

The only penalty for using the respiratory compensation method is that the number of slices available for a given TR may be slightly reduced/increased.

230

Systems also use a method known as _______________ or __________ that times the excitation RF with a certain phase of respiration.

231

___________ is a very general term used to describe a technique of reducing phase mismapping from the periodic motion caused by respiration, cardiac and pulsatile flow motion.

233

_________________ gating uses electrodes and lead wires that are attached to the patient's chest to produce an ECG. This is used to determine the timing of the application of each excitation pulse.

233

____________ gating uses a light sensor attached to the patient's finger to detect the pulsation of blood through the capillaries.

233

__________________ reduces ghosting caused by flowing nuclei moving along gradients.

233

___________ or ___________ produces an image where anatomy that exists outside the FOV is folded onto the top of anatomy inside the FOV.

234

Aliasing along the frequency encoding axis is known as _____________. This is caused by undersampling the frequencies that are present in the echo.

235

A ____________ is used to filter out frequencies that occur outside the selected FOV. Signal originating from outside the FOV along the frequency axis is no longer mismapped as it is filtered out.

239

Anti-aliasing along the phase axis is termed___________, ______________, or _____________, which oversamples along the phase encoding axis by increasing the number of phase encodings performed.

240

______________ produces a dark edge at the interface between fat and water. It occurs along the frequency encoding axis only.

243

Chemical shift can be limited by scanning at lower/higher field strengths and by keeping the FOV to a minimum/maximum.

244

To reduce chemical shift artefact always use the narrowest/widest bandwidth in keeping with good SNR and the smallest/largest FOV possible.

244

At _______ or less, chemical shift artefact is insignificant and usually does not need to be compensated for.

244

When fat and water are in phase and their signals add constructively, and when they are out of phase their signals cancel each other out. This cancellation effect is know as _________________ or _______________.

244

To remedy chemical misregistration, select a __________ that matches the periodicity of fat and water at your field strength.

247

At 1.5 T, for example, selecting a TE that is a multiple of _______ ms reduces chemical misregistration artefact, while at 0.5 T the periodicity of fat and water is ______ ms.

247

___________ artefact produces a banding artefact at the interfaces of high and low signal.

249

_______________ artefact results from under-sampling of data (too few K space lines filled) so that interfaces of high and low signal are incorrectly represented on the image.

249

To remedy truncation artefact, under/over-sampling of data must be avoided. To do so, increase the number of phase encoding steps.

250

_________________ artefact produces distortion of the image together with large signal voids.

250

To remedy magnetic susceptibility artefact, the technologist should:

251

remove all metal objects

use spin echo sequences instead of gradient echo

decrease the TE

___________ and ____________ artefacts appear as adjacent slices in an acquisition having different image contrasts.

252

Adjacent slices receive energy from the RF excitation pulse of their neighbors. This energy pushes the NMV of the nuclei towards the transverse plane, so that they may become saturated when they themselves are excited. This effect is called _______________ and affects image contrast.

253

Nuclei lose their energy due to spin lattice relaxation and may dissipate this energy to nuclei in neighboring slices. This is called ________________.

253

___________ can never be eliminated as it is caused by the natural dissipation of energy by the nuclei.

253

________ artefact appears as a dense line on the image at a specific point.

255

__________ artefact is caused by a leak in teh RF shielding of the room.

256

__________ artefact produces a difference in signal intensity across the image.

256

The main cause of ___________ artefact is uneven excitation of nuclei within the patient due to RF pulses applied at flip angles other than 90º and 180º.

256

To remedy ___________ artefact, always ensure that the coil is loaded correctly and that the patient is not touching the coil at any point.

256

_________ artefact is shown as a black and white banding artefact on the edge of the FOV. It is always seen in gradient echo imaging.

256

The cause of ___________ artefact is a combination of wrap and field inhomogeneity in gradient echo sequences.

256

To remedy ___________ artefact, use spin echo sequences or ensure the patient keeps their arms within the FOV.

257

____________ is seen in tissues that contain collagen (such as tendons) as high signal intensity.

257

___________ artefact is caused when structures that contain collagen lie at an angle of 55° to the main field.

257

To remedy ___________ artefact, alter the angle of the structure or change the TE.

258