Instrumentation Notes- exam 2

What is the primary purpose of uniformity correction in a gamma camera?

To ensure even count density across field of view

Which of the following is the most significant cause of non-uniformity in a gamma camera?

reduced sensitivity near PMT edges

What was the main limitation of the historical “count skimming or adding” technique?

it was purely cosmetic and didn’t fix the underlying cause

Which type of correction is applied at the pixel level to account for difference in energy peaks among PMTs?

energy correction

Linearity correction in a gamma camera is designed to:

ensure that straight lines in the image appear straight

After energy and linearity corrections have been applied, which additional step is used to correct the remaining small variations in camera sensitivity?

acquisition of a high-count uniformity correction map

Why must a separate uniformity correction may be acquired for each isotope used in a department?

because each isotope emits gamma rays of different energies

Which statement best summaries the differences between count skimming and energy/linearity corrections?

count skimming cosmetically balances counts, while energy/linearity corrections produce quantitative accurate data

What potential artifacts results from using a uniformity correction map acquired with insufficient total counts?

statistical noise appearing as false non-uniformity

Which imaging mode would be the most appropriate to evaluate both perfusion and functional washout in a single acquisition?

dynamic mode

If you increase the matrix size from 128 × 128 to 512 × 512 but keep total counts constant, what happens to image noise?

noise increases because each pixel gets fewer counts

Which matrix size would be the most appropriate for a dynamic renal study where timing and count statistics are more important than fine detail?

64 × 64

During a gated cardiac acquisition, the system is set to reject irregular R-R intervals. What is the primary reason for rejecting these regular beats?

to ensure uniform count distribution across all frames for accurate well motion analysis

What is the primary purpose of a look-up-table (LUT) in gamma camera image display?

to convert count values into brightness or color levels for display

When a technologist changes the look-up-tables (LUT) from linear to logarithmic, what happens to the image data?

the low-counts regions become easier to visualize without altering the stored data

Which of the following best describes the function of the collimator in a gamma camera?

defines the field of view and rejects scattered photons

Who developed the first gamma camera and in what year?

Hal Anger, 1958

The primary trade-off when selecting crystal thickness in a gamma camera is between:

sensitivity and spatial resolution

What is the typical material used for the scintillation crystal in a gamma camera?

Na(TI)- Sodium Iodide activated with Thallium

What is meant by the “Z pulse” in gamma camera electronics?

the sum of PMT outputs sent to the pulse height analyzer

Which of the following is a common problem occurring near the edge of the field of view due to PMT geometry?

edge-packing

In digital image storage, increasing the matrix size (e.g., from 64 × 64 to 256 × 256) results in:

smaller pixel size and higher spatial resolution

The sensitivity of a gamma camera is expressed as:

counts per unit of radioactivity (counts/MBq)

A technologist increases the sodium iodide (NaI) crystal thickness from 3/8 inch to ½ inch. Which outcome is most likely? 

improved sensitivity, decreased spatial resolution

A gamma photon interacts within the NaI(TI) crystal and produces light detected by several PMTs. The system determines position based on:

the weighted average of PMT signal outputs

A filed-of-view (FOV) of 40cm is displayed on a 128 × 128 matrix. What is the pixel dimension, and how would doubling the matrix affect spatial resolution?

Pixel = FOV/matrix

0.31 cm per pixel; doubling matrix decreases pixel size, improving resolution

What is a key difference between analog and digital images in nuclear medicine?

analog images require reacquisition if controls are incorrect 

What is the primary limitation of byte mode (8 bits) image acquisition?

risk of pixel saturation

Which acquisition mode stores each detected event with its exact time and (X,Y) location, allowing flexible generation of dynamic frames during post-processing?

list mode

In a gated cardiac study, what is the effect of accepting all R-R intervals including arrhythmic ones?

inaccurate representation of wall motion

What effect does an undersized matrix (e.g. 64×64) have on spatial resolution?

decreases resolution due to larger pixels

When digital zoom is applied, how is the field of view (FOV) affected?

it decreases, focusing on a smaller region

Why dose post-acquisition magnification potentially reduce diagnostic quality compared to digital zoom during acquisition?

it uses interpolation, which can blur fine details

A nuclear medicine technologist wants to zoom in on a specific anatomical region without losing resolution. What is the best approach?

use digital zoom during acquisition to focus on the region

Which matrix size provides the highest spatial reolution?

512 × 512

What is the result of excessive smoothing of a digital image?

flat, less informative image

When the hole diameter of a parallel-hole collimator is increased, what is the primary effect of the image?

spatial resolution decreases and sensitivity increases

A technologist switches from a 20 mm to a 30 mm hole length on the same collimator?

resolution improves slightly, sensitivity decreases