Nuclear Medicine Flashcards

Flashcards based on Nuclear Medicine lecture notes.

What does 'image quality' represent in nuclear medicine?

The accuracy of how the image reflects the real object

Why is high image quality important for technologists?

It helps radiologists get the most accurate picture

What kind of imaging does this lesson mainly focus on?

Planar imaging with the gamma camera

What kind of camera is used for planar nuclear medicine imaging?

Gamma camera

In which way are SPECT and planar imaging related?

SPECT uses planar images to create a 3D image

Select the most accurate statement: Which of the following is a true goal of technologists?

Achieve the highest image quality possible

What does planar imaging NOT provide?

3D images

Why might planar imaging be used before SPECT?

It's simpler and faster for an initial overview

If you improve spatial resolution without adjusting other parameters, what unintended effect might you see in the image?

Increased image noise due to lower count statistics per pixel

Why is balancing noise and contrast especially critical in low-dose pediatric nuclear imaging?

Because low dose decreases count statistics, increasing noise

In which clinical scenario might higher contrast be prioritized over spatial resolution?

Tumor detection in soft tissue

In which way could structured noise mislead a radiologist during interpretation?

It can mimic pathology or mask real abnormalities

Why might improving spatial resolution sometimes lead to worse diagnostic outcomes?

Because it can increase noise, making it harder to detect true abnormalities

Which system factor can directly affect all three: resolution, contrast, and noise?

Collimator design

If two regions of an image have the same resolution and low noise, but one is poorly visualized, what's likely the cause?

Poor contrast between the regions

Why is image noise unavoidable in nuclear medicine, even with a perfect system?

Because radioactive decay is a random process

What is the key difference between physical evaluation and human observer evaluation of image quality?

Physical is objective and measurable, human observer is based on perception

Why are human observer studies still valuable even though they can be subjective?

Because human interpretation is the final step in diagnosis

What could impact the results of a human observer study?

The observer's level of experience and visual acuity

What is one major limitation of human observer performance studies?

They can vary based on personal judgment

Why might computer observer models be used alongside human observers?

To speed up and standardize image quality evaluation

In a clinical setting, which would likely be prioritized first for initial testing of a new imaging protocol?

Human observer studies

What might a disagreement between physical image quality scores and human observer feedback suggest?

That human interpretation considers more than just numbers

What's one advantage of using computer observer models in research?

They reduce the time and variability in evaluating image quality

What is spatial resolution a measure of?

Image sharpness or ability to visualize fine detail

Why do larger collimator holes reduce spatial resolution?

They allow gamma rays at wider angles, blurring the image

Which factor most directly improves spatial resolution in a gamma camera?

Using a high-resolution collimator with smaller holes

How does increasing the distance between source and detector affect resolution?

It worsens resolution due to geometric blur

What is the trade-off when using a collimator with smaller holes?

Reduced sensitivity (fewer photons reach the detector)

Why can collimator resolution be considered a principal limiting factor in nuclear medicine imaging?

Because it fundamentally determines how well spatial details can be localized

A technologist places the patient farther from the detector. Which impact will this have on the spatial resolution?

It will decrease due to increased distance

Which design aspect of the collimator leads to image blur even before the detector processes the signal?

Hole diameter

What is the main source of intrinsic resolution limitations in a gamma camera?

Random spread of light photons across PMTs

What happens to intrinsic resolution as gamma-ray energy decreases?

It becomes poorer

Why does photon distribution among PMTs affect resolution?

Because random spread causes uncertainty in determining where the gamma event occurred

In PET imaging systems, what primarily controls intrinsic resolution?

The size of each detector element

What does intrinsic resolution NOT depend on?

The collimator shape or hole length

Why does higher gamma-ray energy improve intrinsic resolution?

It generates more light photons for better PMT response

What might you expect if PET detectors have large discrete blocks?

Lower spatial resolution

Which of the following would most likely improve image sharpness in a cardiac study?

Using ECG-gated acquisition

Which strategy is used to preserve detail when designing pixel-based image matrices?

Match pixel size to system resolution (2 pixels per FWHM)

What is the purpose of a bar phantom in spatial resolution testing?

To evaluate how clearly the system can differentiate closely spaced lines

Why are phantoms used instead of patients for spatial resolution testing?

To simulate standard conditions and reduce variability

What defines the visibility of bar patterns in bar phantoms?

System resolution compared to bar spacing

What is a possible downside of bar phantom testing?

Some subjectivity in determining resolution cutoff

Why is tungsten sometimes preferred over lead?

Higher density, more effective at blocking gamma rays

What does Full Width at Half Maximum (FWHM) represent on a photopeak curve?

The width of the peak at half of its maximum intensity

What happens if the FWHM is too wide for a given isotope?

Scatter radiation may be misidentified as valid counts

What is the Point Spread Function (PSF)?

A measure of how a point source is spatially blurred by the imaging system

Which of the following best describes the Line Spread Function (LSF)?

It represents how an imaging system blurs a line source

Why is the LSF often used more in practice than the PSF?

It's easier to generate a line source than a perfect point

What does the Modulation Transfer Function (MTF) quantify in imaging systems?

The ability to preserve contrast at different spatial frequencies

Which spatial frequency corresponds to finer image details?

High spatial frequency

In which way is the MTF function typically graphed?

Y-axis: contrast transfer, X-axis: spatial frequency

What is the primary goal of achieving high image contrast in nuclear medicine?

To enhance lesion detectability against surrounding tissues

Which kind of radiopharmaceutical characteristic improves contrast most effectively?

High lesion-to-background uptake ratio

Which of the following is a major contrast-limiting factor in NM?

Superimposed background counting rates

What role does attenuation correction play in contrast?

It removes artifacts and increases lesion-to-background contrast

Which technique can reduce the effect of scattered radiation?

Narrowing the energy window using pulse height analysis

What happens when the energy window is increased from 15% to 50%?

Count rate increases, but image quality decreases

Why does tomographic imaging (SPECT/PET) improve contrast over planar imaging?

It isolates slices and removes superimposed background

What is random noise caused by?

Statistical variation in detected photon counts

Which condition increases the presence of random noise?

Low total count statistics

Structured noise differs from random noise in that it is…

Predictable and pattern-based

Which type of imaging artifact is a ring pattern in SPECT most likely related to?

Structured noise from equipment

Which of the following best describes statistical noise in quantitative terms?

Counts per cm²

What is the occupational dose limit to the whole body per year?

5,000 mrem (50 mSv)

What is the annual dose limit to the lens of the eye for radiation workers?

15,000 mrem (150 mSv)

Which of the following is the non-occupational annual dose limit to the whole body?

100 mrem (1 mSv)

Why is motion during scans a major limiting factor for quality?

It introduces blur and reduces spatial resolution

What is the relationship between FWHM and image quality?

Inversely related the smaller the FWHM, the better the image quality

What does the True Positive Fraction (TPF) represent?

The % of positive images correctly identified

Which shape does a perfect ROC curve take?

Hugging the top-left corner

If the Area Under the Curve (AUC) is 0.5, what does that mean?

The observer/system is guessing

What is the primary purpose of the ramp filter in image reconstruction?

Enhance detail and reduce blurring

In the ramp filter, what happens to high spatial frequencies?

They are amplified

Why is the ramp filter necessary in filtered backprojection?

To correct for the blurring caused by plain backprojection

What happens to image clarity as more projection angles are added?

It improves

Why does simple backprojection cause blurring?

Overlapping of projections outside true object location

What is a sinogram?

A 2D matrix showing projection data across angles

What is the primary goal of simple backprojection?

Reconstruct a 2D cross-sectional image from projection data

What is meant by contrast-to-noise ratio in imaging?

Ratio of useful signal (contrast) vs. background fuzz (noise)

Why are tomographic nuclear methods preferred for oncology?

They show precise lesion depth and location

What is the main goal of tomographic imaging?

To reconstruct cross-sectional images of a 3D object

What's the purpose of Radon's transform in imaging?

Reconstruct images from projection data

What happens after all the projection profiles are collected?

The ECT algorithm reconstructs a 2D image of a slice

What is the purpose of filtering before backprojection?

To reduce blur and improve edge definition

In which way does filtered backprojection reduce image blurring compared to simple backprojection?

By applying a ramp filter before projection

Why is it important to perform backprojection at the same angle each projection was acquired?

To ensure spatial alignment and image clarity

What does the 1-D Fourier Transform do to each profile?

Converts the profile into frequency domain (K-space)

What is the term for the distance between sampling points?

Linear sampling distance

What happens if angular sampling is too sparse?

The image becomes streaky or distorted

Which visual artifact appears with coarser sampling (large r)?

Ring-like or ripple distortions

What is the best way to describe the image acquired at 256 angular samples?

High resolution, minimal artifacts

Why does decreasing angular sampling lead to artifacts?

The system lacks enough viewpoints to reconstruct the image fully

Which function in IR compares estimated and actual profiles to determine how close the guess is to reality?

Cost function

What is the purpose of the Search or Update function in IR?

It adjusts the image estimate based on the cost function output

Which step in the IR process checks if the estimated image and measured projection match?

The 'compare converged?' step

Why is IR more computationally demanding than FBP?

It requires multiple iterations to refine the image

What does Figure 16-18 show about the number of IR iterations?

More iterations improve image clarity and detail