Personal Instrumentation Oral Test Out

How do we do accuracy?

using 3 source (cs-137, Co-57, Ba-133) with an activity over 50 uCi, assay the sources and record the activity, repeat two more times to get an average of the activities.

• ± 5% needs repair; ± 10% replacement

• looking for the systems ability to reporduce

what is the partial volume effect?

it is when there are two different tissues/activities in a voxel, so to deal with that the voxel averages the activities. This creates a blurring look and can cause spill over into surrounding voxels decreasing accuracy and contrast

how do we check sensitivity on a gamma camera

acquire a extrinsic uniformity flood, afterwards take the count rate and divide that by the activity (cps/uCi)

how does longer hole length on a collimator change resolution and sensitivity

it will increase resolution because the photons are less likely to penetrate the lead septa which leads to bad photons, decreasing resolution

it will decrease sensitivity as there are less photons making it through to the crystal to be absorbed and counted

low energy collimator isotopes

• Tc99m, Xe-133, I-123

Medium energy collimator isotopes

In-111, Ga-67

High energy collimator isotopes

I-131

High sensitivity collimator characteristics

larger holes, poor resolution

All purpose collimator characteristics

midsized holes with decent sensitivity/resolution

high resolution collimator characteristics

small holes, thick septa, poor sensitivity

how to perform linearity— Decay method

• start with the highest activity used in the department

• assay the dose

• assay multiple times a day and record

• do until the activity is under 30 uCi

How to perform linearity— sleeve method

• start with the highest activity used in the department

• place source into black sleeve and assay

• start putting into the color sleeve in order of the rainbow and record data

• do until activity is under 30 uCi

• must do within 6 min (Tc T1/2)

how to check uniformity on a SPECT camera

when using a jaszcak phantom, the open space represents uniformity or acquire a flood uniformity like normal

you have an image that looks uniform but during the uniformity QC, uptake shows a hot center and cold edges

the image is averaging the counts

• the middle will always be hotter but the system then labels the middle as above average and the edges as below, the averaging just exposes it

how to perform an intrinsic uniformity

• point source- about 1 mCi tc99m

• place 5 UFOV away

• acquire counts, about 10 million

• if you dont have theb space, use the inverse square law to evenly distribute the counts

  • the ISL applies a mask which increases the edge counts based on how far each pixel is from the center

how to assess spatial resolution on a planar image

• visually using weekly bar phantoms

• quantitively taking the FWHM of the line spread function

how to assess spatial resolution on a SPECT

• visually with a jasack phantom using the rods

• quantitively taking a reconstruction of a line source and measuring the FWHM/FWTM in different directions

as a parallel hole collimator gets closer, how does it change the size of the fov

it does not change anthing

what is the benefit of elliptical and contour orbit over circular

they both can get much closer to the patient and improve the quality and resolution of the image

what does getting super close to the patient improve

resolution

how do you measure 3D resolution

jaszak phantom with the rods

how do you measure 2D resolution

with a bar phantom and the FWHM of the line spread function

what do the components of a jaszack phantom do

• rods= spatial resolution

• spheres= contrast

• open space= uniformity

how do you close a department

• survey all areas to check for contamination

• check out all packages so they can be picked u

• set up QC if needed

• survey hands and feet

• lock all doors to department. specifically the hot lab and anywhere else sources might be

you have a patient with a cold spot on a hot background and another patient with a hot spot on a cold background, which will be harder to detect due to the partial volume effect

a cold spot on a hot background, the counts from the background will start to average and spill over into the cold lesion making it seem hotter than it is or completely mask it

what happens if you put a point source too close on an intrinsic uniformity scan and how to correct for it

the image will be non-uniform with a very intense center. correct it using the inverse square law to correct for the counts by increasing the cts at the edge based on the distance to the middle

how and why do we do CORs

we do them to assure the alignment is accurate with the rotation and can be applied with the AOR for corrections

• 1 mCi tc point source

• place of the AOR

• 32 stops, 360º, 5s/stop