Physics 2 Quiz 1.1

This statement is false because for a constant velocity, the time taken to travel through a slice of any thickness would be the same. The velocity of the nuclei remains constant, meaning that the distance traveled per unit time remains constant as well. Therefore, the thickness of the slice does not affect the time taken for the nuclei to travel through it.

The entry slice phenomenon refers to the occurrence when moving protons, typically perpendicular to the slice plane, appear brighter in the first slice compared to the rest of the slices. This phenomenon is observed in magnetic resonance imaging (MRI) and is caused by the specific imaging parameters used. It is important to be aware of this phenomenon in order to accurately interpret MRI images.

Even echo rephasing refers to the technique of acquiring the second and succeeding even echoes at multiples of the first echo time (TE) in a spin echo pulse sequence. This helps in reducing intra-voxel dephasing, which can occur when there are multiple echoes produced. By acquiring the even echoes at specific time intervals, the dephasing effects can be minimized, leading to improved image quality and better identification of structures within the image.

The explanation for the answer "False" is that co-current flow, in regards to entry slice phenomenon, is when the moving protons are traveling in the same direction as the slice direction. This makes the entry slice phenomenon more pronounced, not less pronounced.

The correct answer is 2.2 ms. Out of phase TE refers to the time it takes for the transverse magnetization to reach its maximum amplitude after the application of the 90-degree RF pulse. At 1.5T, the approximate value for the out of phase TE is 2.2 ms.

When a flowing nucleus is adjacent to a stationary nucleus in a voxel, there is a phase difference between the two nuclei. This phase difference arises due to the different magnetic field experienced by the flowing and stationary nuclei. The flowing nuclei experience a different magnetic field due to their motion, leading to a phase shift in their signals compared to the stationary nuclei. This phase difference can be utilized in various imaging techniques to differentiate flowing and stationary tissues, such as in phase-contrast magnetic resonance imaging (PC-MRI).

When a coronal saturation region is placed anterior to the cervical spine to eliminate motion artifacts from swallowing, the Y gradient must be turned on during the transmission of the initial saturation 90 degree RF pulse. This is because the Y gradient is responsible for controlling the phase encoding direction in the coronal plane. By turning on the Y gradient, the RF pulse will be transmitted in the correct direction to effectively saturate the desired region and minimize motion artifacts.

Fast Spin Echo is not a way of compensating for flow phenomena. Fast Spin Echo is a type of magnetic resonance imaging (MRI) sequence that is used to acquire images quickly. It is not specifically designed to compensate for flow phenomena, which refers to the movement of fluids within the body. Gradient Moment Nulling, Even Echo Rephasing, and Spatial Presaturation are techniques that are used to compensate for flow phenomena in MRI imaging.

The SAT TR is equal to the scan TR divided by the number of slices. This means that the total time it takes for a single scan repetition (SAT TR) can be calculated by dividing the scan TR (the time it takes to complete one full scan) by the number of slices (the number of slices being acquired during each scan).

The precessional frequency difference of fat and water at 1.0T is 147Hz. This means that the magnetic resonance frequency of fat is 147Hz higher than the magnetic resonance frequency of water at a magnetic field strength of 1.0T. This frequency difference is important in magnetic resonance imaging (MRI) as it allows for the differentiation and imaging of different tissues based on their unique precessional frequencies.

The magnitude of the entry slice phenomenon is influenced by several factors. Slice thickness plays a role as it determines the thickness of the slice being imaged, affecting the amount of signal from the flowing blood. The velocity of flow is also important as it determines the speed at which the blood is moving through the slice, impacting the signal intensity. The direction of flow is relevant as it determines the angle at which the blood is entering the slice, affecting the magnitude of the entry slice phenomenon. TR (repetition time) is not relevant to the entry slice phenomenon, and neither is the matrix or FOV (field of view).

The flow that is in the same direction as the slice selection is called co-current. In this case, the flow of the current is perpendicular to the direction of the slice selection.

The phenomenon of entry slice increase occurs at the first slice in the stack, when using a long TR, and in thin slices. This means that when acquiring images, there is an increase in signal intensity at the entry slice compared to the subsequent slices. This can be attributed to factors such as T1 relaxation time, which affects the recovery of longitudinal magnetization, and the slice profile, which can cause partial volume effects. Additionally, using a long TR and acquiring thin slices can further enhance this phenomenon.

The addition of saturation pulses in a pulse sequence is expected to decrease the maximum number of slices that can be obtained. Saturation pulses are used to suppress the signal from certain tissues, which reduces the overall signal intensity. As a result, the signal-to-noise ratio decreases, making it harder to distinguish individual slices and lowering the maximum number of slices that can be acquired. Therefore, the maximum number of slices is expected to decrease when saturation pulses are added.

Fat saturation is a technique used in magnetic resonance imaging (MRI) to suppress the signal from fat tissues, which can cause artifacts in the image. However, it is not effective in reducing motion artifacts created by blood flowing through the sagittal sinus. The sagittal sinus is a large vein located in the midline of the brain, and its motion can cause artifacts in the image. Fat saturation is not specifically designed to address motion artifacts caused by blood flow, so it would not be effective in this case.

Turbulent flow is characterized by chaotic and irregular movement of fluid, resulting in mixing and moving in more than one direction. This type of flow is typically found in tortuous sections, distal to bifurcations and stenosis, where there is a great deal of dephasing. However, turbulent flow does not have a lower chance of inaccuracy on an image. In fact, turbulent flow can cause image artifacts and make it more difficult to accurately interpret images.

Gradient moment nulling and flow compensation are techniques used in magnetic resonance imaging (MRI) to minimize artifacts caused by flowing spins. Gradient moment nulling involves applying gradients to cancel out the effects of flow-induced phase shifts, while flow compensation is used to minimize signal loss due to flowing spins. Both techniques aim to improve image quality by reducing artifacts caused by flowing spins. Therefore, the correct answer includes both gradient moment nulling and flow comp.

Gradient Echo is the correct answer because it does not naturally offer dark blood without any special imaging requirements. Gradient Echo sequences are sensitive to flowing blood and can produce bright blood signals, unlike the other imaging techniques mentioned. Inversion Recovery, Fast Spin Echo, and Spin Echo sequences can all naturally provide dark blood without any additional imaging requirements.