MRI Imaging Quiz Part 2: Sequences and Contrast

TR stands for repetition time, which is the time interval between successive radiofrequency pulses in an MRI scan. It primarily affects T1 weighting because a longer TR allows for more longitudinal magnetization recovery, resulting in a higher T1 contrast between tissues. On the other hand, a shorter TR reduces the T1 contrast and enhances T2* weighting. Therefore, the choice of TR plays a crucial role in determining the T1 contrast in MRI images.

In a T2 weighted image, tissues with long T2 relaxation times appear hyperintense. This means that these tissues appear brighter compared to other tissues in the image. The long T2 relaxation times indicate that these tissues have a slower rate of returning to their original state after being excited by the magnetic field. As a result, they emit a stronger signal and appear hyperintense in the image.

The image parameter that primarily affects T2 weighting is TE, which stands for Echo Time. TE refers to the time between the radiofrequency pulse and the peak of the echo signal received from the patient. T2 weighting refers to the contrast in the image that is primarily determined by the relaxation time T2 of the tissues. By adjusting the TE, the image can be weighted to highlight certain tissues with longer T2 relaxation times.

In a T2 weighted image, CSF has a long T2 relaxation time, which means it takes longer for the protons in CSF to return to their equilibrium state after being excited. As a result, CSF appears bright in the image.

A 180 degree RF pulse is used to refocus the dephasing net vector in the transverse plane. When the net magnetization vector is subjected to various magnetic field gradients, it can become dephased, resulting in loss of signal. By applying a 180 degree RF pulse, the dephased spins are flipped back into alignment, effectively refocusing the net vector and restoring the signal.

A T1 weighted image is created by using a short TR (repetition time) to maximize the contrast between tissues with different T1 relaxation times. This results in a high signal intensity for tissues with short T1 relaxation times, such as fat, and a low signal intensity for tissues with long T1 relaxation times, such as fluid. Therefore, the correct answer is MAX T1.

The Y gradient alters the magnetic field strength along the vertical axis. This means that it changes the strength of the magnetic field in the up and down direction. The other options, horizontal, long, and short, do not describe the axis along which the magnetic field strength is altered.

During slice selection, the Y gradient is used to select slices in the coronal plane. The coronal plane is a vertical plane that divides the body into front and back sections. By using the Y gradient, the magnetic field is manipulated to excite and detect signals from slices in this specific plane. This allows for the creation of images that show structures from a front-to-back perspective.

The X gradient alters the magnetic field strength along the horizontal axis.

The correct answer is "RECIEVE BANDWITH." In frequency encoding, a range of frequencies is sampled. The term "receive bandwidth" refers to the range of frequencies that can be received or detected by a system. Therefore, it is the most appropriate option for describing the range of frequencies that is sampled during frequency encoding.

The signal created after applying a 90 degree RF pulse is known as Free Induction Decay (FID). When the RF pulse is applied, it tips the magnetization vector by 90 degrees, causing it to precess around the magnetic field. As the spins dephase and relax back to their equilibrium state, they emit a decaying signal, which is called the FID. This signal contains information about the underlying tissue properties and is used in various magnetic resonance imaging (MRI) techniques.

The time between the 90 degree RF pulse and the spin echo signal in a spin echo pulse sequence is known as TE, or echo time. This is the time it takes for the signal to return after the RF pulse is applied. TR, or repetition time, refers to the time between successive RF pulses. Inversion time is the time between an inversion pulse and the 90 degree RF pulse, and relaxation time refers to the time it takes for the protons to return to their original state after excitation.

In the acquisition of axial images of the brain with the frequency direction A/P, phase encoding is performed by the X physical gradient.

In MRI imaging, frequency encoding is performed using the physical gradient in the X direction. This means that the gradient is applied along the left-to-right axis of the body. By applying this gradient, the MRI scanner can differentiate between different frequencies of the signal emitted by the body's tissues, allowing for the creation of detailed axial images.

In the acquisition of axial images of the body with the frequency direction L/R, phase encoding is performed by the Y physical gradient. This means that the Y gradient is used to encode the phase information of the image, allowing for the spatial localization of the signal. The Y gradient is applied during the data acquisition process to generate the necessary phase shifts in the signal, which are then used to reconstruct the image in the correct spatial orientation.

Grey matter refers to the region of the brain that contains neuronal cell bodies. T2 relaxation time is a measure of how quickly the magnetic resonance signal decays after a radiofrequency pulse is applied. In this case, at a field strength of 1.0 tesla, the approximate T2 relaxation time for grey matter is 100MS. This means that the signal from grey matter takes approximately 100 milliseconds to decay after the radiofrequency pulse.

The phase encoding gradient is known as the Y gradient. In magnetic resonance imaging (MRI), the phase encoding gradient is used to encode spatial information along the Y-axis. It is applied during the imaging process to create a phase shift in the protons, allowing for the differentiation of signals from different locations in the Y direction. The X and Z gradients are used for encoding information along the X and Z axes, respectively. Therefore, the Y gradient is specifically referred to as the phase encoding gradient.

The T1 relaxation time refers to the time it takes for the longitudinal magnetization of a tissue to recover to 63% of its original value after being perturbed. In this question, at a field strength of 1.0 tesla, the approximate T1 relaxation time for renal cortex tissue is 360. This means that it takes approximately 360 milliseconds for the longitudinal magnetization of renal cortex tissue to recover to 63% of its original value after being perturbed at a field strength of 1.0 tesla.

When the phase encoding gradient is activated, steep slopes produce a low signal amplitude. This is because the steep slopes cause the dephasing of protons, leading to a decrease in the signal strength. In contrast, shallow slopes produce a high signal amplitude as they cause less dephasing of protons. Therefore, the correct answer is LOW.

At a field strength of 1.0 tesla, the approximate T1 relaxation time for CSF is 2000MS. T1 relaxation time refers to the time it takes for the longitudinal magnetization of a substance to recover to 63% of its original value after being perturbed. In this case, CSF (Cerebrospinal Fluid) has a T1 relaxation time of approximately 2000MS at a field strength of 1.0 tesla. This means that it takes around 2000 milliseconds for the magnetization of CSF to recover to 63% of its original value after being disturbed.

At a field strength of 1.0 tesla, the approximate T1 relaxation time for renal medulla tissue is 680.

In a 1.0 tesla magnet, the precessional frequency of fat is higher than that of water. The difference in the precessional frequency between fat and water is 147.

At a field strength of 1.0 tesla, the approximate T2 relaxation time for spleen tissue is 80MS. T2 relaxation time refers to the time it takes for the protons in a tissue to lose their phase coherence after being excited by a magnetic field. At a higher field strength, the T2 relaxation time generally decreases. Therefore, at a field strength of 1.0 tesla, the T2 relaxation time for spleen tissue is approximately 80MS.

At a field strength of 1.0 tesla, the approximate T2 relaxation time for renal medulla tissue is 140.

At a field strength of 1.0 Tesla, the approximate T1 relaxation time for blood is 800. T1 relaxation time refers to the time it takes for the longitudinal magnetization of the protons in a substance to recover to its equilibrium state after being perturbed. In this case, at a field strength of 1.0 Tesla, the blood has an approximate T1 relaxation time of 800.

At a field strength of 1.0 tesla, the approximate T2 relaxation time of fat is 40. The T2 relaxation time refers to the time it takes for the signal from fat to decay after an initial excitation. In this case, at a field strength of 1.0 tesla, the T2 relaxation time of fat is approximately 40.

At a field strength of 1.0 tesla, the approximate T2 relaxation time for renal cortex tissue is 70MS. This means that it takes approximately 70 milliseconds for the protons in the renal cortex tissue to return to their equilibrium state after being excited by a magnetic field. T2 relaxation time is a measure of how quickly the protons lose their phase coherence and is influenced by the tissue's composition and microstructure.

At a field strength of 1.0 tesla, the approximate T1 relaxation time for muscle tissue is 600. T1 relaxation time refers to the time it takes for the longitudinal magnetization of a tissue to recover to 63% of its original value after being disturbed by an external magnetic field. In this case, at a field strength of 1.0 tesla, the muscle tissue takes approximately 600 milliseconds to recover to 63% of its original magnetization.

At a field strength of 1.0 tesla, the approximate T1 relaxation time for spleen tissue is 480. This means that it takes approximately 480 milliseconds for the excited protons in the spleen tissue to return to their equilibrium state after being excited by the magnetic field. The T1 relaxation time is a measure of how quickly the protons in a tissue relax and is influenced by factors such as molecular motion and interactions.