W2: Introduction to MRI

What is the primary focus of MRI imaging?

Human brain imaging.

What component detects signals from the brain in MRI?

The receiver (or head) coil.

What is the role of the transmitter coil in MRI?

It produces the signal.

What type of coils are essential for localizing signals in MRI?

Gradient coils.

How do gradient coils function in MRI?

They are small electromagnets that alter the magnetic field strength.

What unit measures the main magnetic field strength in MRI?

Tesla (T) units.

What are the field strengths for clinical and research MRI scanners?

Clinical scanners: 1.5 T; Research scanners: 3 T or above.

How much stronger is the magnetic field in MRI compared to Earth's magnetic field?

At least 104 times stronger.

What atomic nuclei does MRI primarily focus on?

Hydrogen protons.

What phenomenon describes how protons react in a magnetic field?

Precession.

What frequency corresponds to the Larmor frequency for a 1.5 T scanner?

Just under 64 MHz.

What is the significance of the Larmor equation in MRI?

It defines the precession frequency of protons in a magnetic field.

What is longitudinal magnetization in MRI?

The net magnetic force aligned along the direction of the magnetic field.

What happens during T1 relaxation in MRI?

High-energy protons transition to a lower energy state, releasing energy as heat.

What does T2 relaxation refer to in MRI?

The dephasing of protons that results in a loss of transverse magnetization.

How does water compare to fat in terms of T1 and T2 relaxation times?

Water maintains transverse magnetization longer than fat.

What are voxel and pixel definitions in MRI imaging?

Pixel: 2D image point; Voxel: 3D equivalent of a pixel.

What does TR stand for in MRI imaging?

Repetition time.

What does TE stand for in MRI imaging?

Echo time.

What does spatial resolution refer to in neuroimaging data?

The detail in images, where smaller voxel sizes lead to higher spatial resolution.

What type of data is fMRI primarily based on?

Contrasting brain activity between experimental tasks.

What does noise in neuroimaging analysis refer to?

Unwanted signals that obscure or distort the true data.

What is the purpose of pre-processing in neuroimaging data analysis?

To increase signal to noise ratio (SNR) and remove sources of noise.

What does the multiple comparisons problem entail in neuroimaging analysis?

When conducting multiple tests, a single p-value may be insufficient without correction.

What is the imager’s fallacy?

Assuming two results are the same just by looking at them side by side without statistical comparison.

What is a common statistical test used in neuroimaging?

Student’s t-test.

What is the purpose of machine learning in neuroimaging?

To find patterns in data and classify it based on training.

What are ICAs in the context of neuroimaging?

Independent Component Analyses are pattern-matching techniques used to analyze simultaneous brain signals.

Define voxel-based analysis in neuroimaging.

Analysis done on data at the level of individual voxels.

What does T1-weighted imaging emphasize in MRI?

Differences in longitudinal relaxation times of tissues.

What does T2-weighted imaging highlight in MRI?

Differences in transverse relaxation times, especially showing CSF as bright.

What is the significance of the slice thickness in 3D imaging?

It is the measurement of each 2D slice of the 3D volume.

What is a common challenge when analyzing neuroimaging data?

Correlating brain activity with experimental tasks.

What are the two main conventions for storing fMRI data?

XYZ-T orientation and XYT-Z orientation.

What is the typical temporal resolution of fMRI data?

In the seconds (s) range.

How is longitudinal magnetization restored in MRI?

By energy release during the T1 relaxation process.

What structure influences the T2 relaxation time of fat?

Its more rigid structure.

How do protons begin to behave when excited by radiofrequency pulses?

They synchronize their precession in the transverse plane.

What is indicated by higher spatial resolution in neuroimaging?

More details in the imaging due to smaller voxel sizes.

What experimental model is typically used in data modeling for neuroimaging?

The general linear model.

What are time series in neuroimaging analysis?

Basic building blocks generated by extracting intensity values over time.

What is the role of gradient coils in image localization?

To finely tune the magnetic field across all 3 dimensions.

What is the effect of head motion in neuroimaging?

It introduces noise that can disrupt the signal quality.

What is the relationship between voxel intensity and scanner resolution?

Higher resolution results in more consistent and defined voxel intensities.

What distinguishes qualitative imaging from quantitative imaging?

Qualitative imaging focuses on arbitrary voxel intensities, while quantitative imaging correlates values with actual tissue properties.

What is the advantage of conducting a whole brain analysis?

To explore all regions of the brain, although it may raise multiple comparison issues.

What is an analysis scope in neuroimaging?

Determining whether to perform a whole brain analysis or focus on specific regions of interest (ROIs).

How does physiological noise affect neuroimaging data?

It can introduce variability that may obscure true brain signals.

What are common biases in exploratory analysis of neuroimaging?

Over-interpreting results and double dipping (circular analysis).

What type of errors can occur during neuroimaging analysis?

Type 1 errors due to inadequate correction for multiple comparisons.

What does the Bonferroni correction address in neuroimaging?

It tries to control the false positive rate when multiple comparisons are made.

What experimental technique is often used to define ROIs in neuroimaging?

Meta-analysis.

What key challenge arises from running many statistical tests in neuroimaging?

The increased risk of Type I errors.

In what context is the term 'the data are' used correctly?

In reference to plural data in neuroimaging.

What is the purpose of smoothing in neuroimaging data processing?

To reduce variability and enhance the consistency of anatomical features.

What device is primarily used for neuroimaging-related scans?

MRI scanner.

What does the structure of the brain include in MRI terms?

Grey matter, white matter, and cerebrospinal fluid (CSF).

How long do fMRI data acquisition snapshots typically last?

A few seconds.

What does the magnetic field in MRI allow protons to do?

Align and precess, facilitating imaging.

What is a common trait of hydrogen protons in tissue during MRI?

They act like tiny bar magnets due to their positive charge.

What are the three gradients in MRI used for localization?

Slice gradient (Gs), Phase-encoding gradient (Gp), Frequency-encoding gradient (Gr).

What does CSF appear as in T2-weighted images?

Bright.

What are higher magnetic field strengths associated with in MRI?

Improved imaging performance and higher manufacturing costs.

In the absence of a strong magnetic field, how are protons aligned?

Randomly aligned, cancelling out magnetic effects.

What is the ultimate goal of MRI in terms of signal localization?

To localize the signal into 3D space.