Category Archives:Quality Control

What You’re Missing in Your Symbia Gamma Camera QC

Leave a comment Nuclear Medicine, Quality Control
What You're Missing in Your Symbia Gamma Camera QC

In this post, we’re going to be talking about something that you might not know about your Siemens Gamma Camera quality control.  

We’re going to be talking about the very popular, widespread Siemens Symbia, and this post is going to cover every version of Symbia that’s out there, because for this purpose, the same issue is present. 

What we’re going to be talking about is uniformity and how we evaluate the uniformity images on a Siemens Gamma Camera.

There’s one aspect of evaluating the uniformity images that a lot of technologists don’t really know.  And unfortunately, the reason is because the essential information is buried in the quality control portion of the manual.  

Watch the video above on our YouTube channel as Eric explains what you may be missing during your Siemens Symbia Gamma Camera quality control.

Deep inside the Quality Control portion of your Siemens Symbia gamma camera is a section on the criteria for evaluating the uniformity of images. Follow along  as we show you where to find this important information.

Standard Uniformity Analysis

Often nuclear medicine technologists are taught to evaluate the quantitative part of the uniformity analysis by looking at the numbers and making sure that it’s less than 5%. 

This is a general rule of thumb. 

But for the Siemens system, there are actual values or limits that are associated with each of the four quantitative metrics that we get when completing daily quality control. 

So, let’s dive into the quality control manual and show you what those metrics are and show you why it’s important. As a note, for this post, we are using the Operator’s Manual for the Siemens Symbia Intevo 16/6/2 and Intevo Excel Series.

Cover Page for Siemens Symbia Gamma Camera

Uniformity Values

Within the Operator’s Manual, we can find the specific Uniformity Values by turning to the Quality Control and Assurance section.

For our example in this post, if you look on page 290, you can find a table with Uniformity Values. And while a general rule is to have values less than 5%, you can see from the table that each value is unique.

The table provides the values for Integrated CFOV, Integrated UFOV, Differential CFOV, and Differential UFOV. 

Each of these values is different because each of measuring using unique criteria measuring a different physical aspect of the image. Note that these are all intrinsic values for 10 million counts.

Intrinsic Uniformity Values

Now that we’ve found the intrinsic uniformity values, we can find the extrinsic values on page 301 of the Operator’s Manual in our example. We can see that this set of criteria are slightly different.

We still have 6% and 5% for the Integrated CFOV and UFOV. However, for the Differential, now we’re at 3.5% for CFOV and 4% for UFOV.

Whenever we’re doing our flood images, we need to make sure that we’re looking at the intrinsic criteria for any intrinsic floods that we’re doing, and we’re should be looking at the extrinsic criteria for any extrinsic floods that we’re doing. Again, these are for 10 million count floods and this is for the intrinsic verification or the extrinsic verification.

Extrinsic Uniformity Values

Example of a Uniformity Value Comparison

In this example, we will use an intrinsic verification from a Siemens MBA. When we look at each of the numbers. The reason we use this specific example is because there is no indication on the screen image that this flood actually didn’t pass.

So which criteria did not pass?

Side-By-Side Analysis

Let’s just do a side by side against what the intrinsic values are versus what we actually calculated or measured.

When reviewing the image results with the actual values in the Operator’s Manual Quality Control section, we can see that we’re fine with everything here except for Detector 1, Integrated UFOV. This value shows 3.19%, yet the criteria is only 3%.

Uniformity Value Comparison
Intrinsic Uniformity Values

There is no indication on the screen that one of the values hasn’t passed the QC standard. This is somewhat problematic with the Siemens systems because you don’t actually know whether you pass or fail the criteria automatically. You have to apply the criteria from the manual to determine whether or not you pass or fail the the test. 

What Do You Do If a Value Fails?

So if you have a value that fails like this 3.19%, when the criteria is 3%, what do you do?

The first thing we recommend to people to do is to go through a tuning and peeking exercise on the equipment. Go through the tuning and peaking exercise, do all of the things that you can run before you get to the uniformity test and then rerun the flood.

Oftentimes that will correct the issue. If that doesn’t correct the issue, you can go back in and rerun and an intrinsic calibration. When you run an intrinsic calibration, we sometimes call that a high count flood. With the Siemens systems, you need to do at least 120 million counts. 

Oftentimes they’re set to 200 million counts, and this can be quite timely. But when you’re redoing that intrinsic calibration you’re going to smooth out any non uniformity that you see in the intrinsic verification. When you do the intrinsic calibration, there is a specific criteria associated with it that you can find in the manual.

For intrinsic calibrations, we say that they can compensate for values up to about 10%. If you exceed 7% for the calibration, then you need to contact service. If your intrinsic calibration passes and you don’t see any issues, you’re below the 7% on the intrinsic calibration. 

Now you can rerun your intrinsic verification or daily flood and see if you you pass those values. If you are still not passing those values, that’s the point that you should probably contact either service or contact your physicist to try to get some direction on what it is that you need to do in order to get your camera to pass the manufacturer stated specifications.

A Common Misconception

There’s a common misconception that the screen will turn red if a Verification Flood value fails. As long as it doesn’t turn red, you’re going to be fine.

That’s actually not true with the Siemens systems. You have to pay attention to what the values are and evaluate against what’s in the manual to determine whether or not your uniformity images are actually passing the manufacturer’s specifications.

We hope that this article and video has provided you with awareness of things to consider when testing your Symbia Gamma Camera to ensure it pass the manufacturer’s standards. If you have questions or comments, please reach out to us at info@olympichp.com and we’d be happy to assist you. 

Your medical physicist is a great resource for you when designing your Quality Control Program, nuclear medicine testing, and ACR accreditation.  You can also always reach out to us if you have questions or want more information on why you should partner with us. 

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How to Evaluate a SMPTE Pattern

Leave a comment Quality Control

What is a SMPTE pattern?

SMPTE is an acronym that stands for the Society of Motion Picture and Television Engineers. It’s a test pattern used in medical imaging to evaluate the quality of the imaging monitors.

 

Watch the video above on our YouTube channel as Eric walks you through how to evaluate a SMPTE pattern when completing your monthly visual quality control checklist for CT scanners. 

So, why is this important to understand?

First, visually inspecting the SMPTE pattern can identify any problems with the quality of the imaging monitor. As a radiologic technologist, it’s critical that the monitor is providing consistent and accurate results.

Second, checking the SMPTE pattern on a CT scanner is part of the monthly visual quality control checklist for the scanner required by the ACR or the American College of Radiology.

On page 48 of the ACT CT Quality Control Manual, available here, they provide the specific procedures for testing the gray level performance of CT scanner acquisition display monitor.

You can also download the ACR CT Equipment Quality Control Data Form to record your daily and monthly inspections.

The SMPTE Test Pattern

What do you need to look for?

There are three main areas to visually check when inspecting the SMPTE pattern on the imaging monitor.

The 5% and 95% patches within the SMPTE pattern.

1. The 5% patch

You want to be able to clearly identify the 5% patch within the 0%-5% square, ensuring it’s discernible.

The 5% patch is found directly to the right of the 0% gray level box, which is solid black.

2. The 95% patch

You want to be able to clearly identify the 95% patch within the 95%-100% square, ensuring it’s discernible.

The 95% patch is found directly to the left of the 100% gray level box, which is solid white.

Each of these patches must be discernible in order to pass the monthly quality control check.

3. The gray level steps

You can identify the distinct gray level steps throughout the SMPTE pattern.

On the SMPTE pattern, you should be able to identify eleven (11) distinct gray scale boxes from solid black to solid white. 

There are also two (2) boxes of 50% gray – both of these squares should be identical. 

 

The individual gray scale boxes of the SMPTE pattern.

On the right hand side of the ACR CT Equipment Quality Control Data Form you will find a box for the Monthly Display Monitor Gray Level.

As you check each of the three above areas, indicate its passing with a checkmark or “P” for Pass. For a failing test, you may enter “F” for Fail.

What do you do if you can't see those patches? Or you don't have distinct grade level steps?

Here are several tips:

  1. Ensure you use the same lighting conditions every time you evaluate the SMPTE pattern for your monthly visual inspection.
  2. Ensure that the monitor is positioned so that there’s no glare from existing lighting or excessive ambient light.
  3. Ensure that the monitor hasn’t entered an automatic power-saver or economy mode.
  4. A common issue is incorrect adjustment of the monitor’s contrast and brightness settings. If you suspect this may be the case, perform the manufacturer’s recommended procedure for adjusting the monitor’s contrast and brightness.

If you’re still having issues seeing the distinct 5% and 95% patches or cannot observe the gray level steps after going through the above tips, you will want to contact your service engineer or medical physicist. They can provide recommendations on how to correct the issue. Alternatively, the monitor may need to be repaired or replaced.

 

Now that you understand what a SMPTE pattern, you can confidently evaluate it during your CT scanner monthly inspection.

If you have any questions or comments, we welcome you to reach out at info@olympichp.com

Also, check out our Resources page for further information on quality control documentation, forms, and manuals.

 

Your medical physicist is a great resource for you when designing your CT Scanner Quality Control Program.  You can also always reach out to us if you have questions or want more information on CT Quality Control or want to see why you should partner with us.  We also offer Annual CT Physics Testing.

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How To Perform Weekly MRI Quality Control For The ACR

Leave a comment Quality Control

Sitting at the MRI console, I reach for the Quality Control binder.  I glance at the MRI Technologist who has a look of panic and fear on their face.  It’s the kind of look that says, “Please don’t look in there, I know this isn’t going to be good.”  I thumb through the pages and notice weeks of missing Quality Control and a smattering of failed results.  You see, I’m a physicist.  And in my time reviewing Quality Control, this is a common scenario.  Balancing the competing priorities in an MRI department and Quality Control can become an afterthought.  Compounding the issue is that much of the guidance for performing MRI Quality Control is written by physicists for other physicists.  Not for technologists.  So, what makes this guide any different?  Well, before I went off to be a physicist, I was a technologist myself.  And I quite enjoy putting on my technologist-hat from time to time.  This guide is written with straightforward, step-by-step instructions and minimal physics jargon.  And we might even have a little fun along the way.  With that in mind, let’s get after it.

Key Point: A well-designed, well-documented, and reliably executed quality control (QC) program is essential to consistent production of high-quality MR images and is a key component of ensuring quality and safety in the MR Environment.     

What Are The Requirements?

The requirements fall into 4 basic categories.  The phantom, the frequency, the tests, and the documentation.

The Phantom

There are two phantoms that are approved by the American College of Radiology (ACR).  There is the Large MRI Accreditation Phantom and the Small MRI Accreditation Phantom.  The Large Phantom is used for whole body scanners while the Small Phantom is used for extremity scanners.  This article will focus on the Large MRI Accreditation Phantom.  And if you’re in need of purchasing a phantom, check out the phantoms offered by Supertech.

The Frequency

The ACR “strongly recommends” performing QC testing on a daily basis.  That’s right, I said a daily basis.  While I’m sure there are sites that perform MRI QC on a daily basis, I have not run into them.  The minimum QC frequency is weekly, which is what the majority of sites are doing.  Stick with a weekly QC schedule and you’ll be doing brilliantly.

Large MRI Accreditation Phantom

Pro-Tip: Schedule to perform your QC at the same time on Monday of each week.  This way if scheduling issues arise, equipment fails, or you simply forget then you have additional days in the week in which you can still complete your QC requirements.

The Tests

We’re going to cover performing each test in detail in the following sections.  But to give you a preview, the tests we’ll be performing are Table Position Accuracy, Center Frequency & Transmitter Gain, Geometric Accuracy, High Contrast Spatial Resolution, Low Contrast Detectability, and Artifact Evaluation.  We’ll also need to perform the Visual Checklist, which has separate documentation.

The Documentation

Documentation should be done on either the Weekly MRI Quality Control Spreadsheet published by the ACR or on your own form.  You can check out our own handy MRI Quality Control template where you can input your scanner information and action limits and you’ll instantly know if a test didn’t pass by highlighting your result in red.  The best part is, it’s free!  Additionally, the MRI Accreditation Program Visual Checklist must be completed on a weekly basis.  These documents should be reviewed for completeness on an annual basis by your medical physicist.

Let's Do Some QC!

Phantom Setup

The large phantom should be positioned in the head coil so that it is in the center of the coil in the left/right and anterior/posterior direction.  This is relatively easy to do using a phantom cradle for accurate and repeatable results.  Alternatively, you can use a stack of computer paper to ensure the phantom is centered within the coil.  Using the same stack of paper will be important to reproduce your results from week to week. 

Phantom Cradle
ACR Phantom with Computer Paper

Use a level to ensure the phantom is level in all directions.  Do this by placing the level on the front bar of the phantom and also on the top of the phantom.

Move the phantom into position within the scanner using the laser to complete the positioning. The laser should be positioned so that 80% of the laser is on the grid structure and 20% is off the grid structure.  How do you determine if 80% of the laser is on the grid?  Just aim for having the majority of the laser line on the grid and a little bit off of the grid and you’ll be fine.

Send the phantom to isocenter and you’re now ready to scan!

Scanning The Phantom

A three-plane localizer should be used to ensure the phantom is properly positioned, followed by the acquisition of a sagittal localizer.  The ACR sagittal localizer sequence should use the following parameters.

Sagittal Localizer Imaging Parameters

Pulse SequenceSpin Echo
TR200 ms
TE20 ms
FOV25 cm
Number of Slices1
Slice Thickness20 mm
Slice GapN/A
NEX (Averages)1
Matrix256 x 256
Scan Time51-56 seconds

Table Position Accuracy

After acquiring the sagittal localizer, review the image.  You’ll need to make measurements on the Sagittal Localizer to verify the Table Position Accuracy.  Each manufacturer is slightly different, but the principle is the same.  Turn on the “Grid” function and you’ll have a horizontal line and a vertical line superimposed on the Sagittal Localizer.  This is your X and Y axis.  In this case, we don’t care about the Y axis.  On the image, take a measurement from the X axis to the top of the grid structure in the phantom.  The grid structure in the phantom is denoted by the 11 little vertical black lines on the image.

Another option may be to turn on the cursor and hover over the image at the top edge of the grid structure.  In the example below, we can see the cursor is at a position of S 0.00 mm.  This means the top edge of the grid structure is exactly at isocenter.

Table Position Accuracy Example with Grid Turned On
Table Position Accuracy Example with Cursor

Action Criteria: The top edge of the grid should be within ± 5mm of isocenter.

If the location of the top edge of the grid structure is within ±5 mm of isocenter, enter “YES” in the column designated “Accuracy OK?”

If the computer booted without a problem and the scanner interface works properly, enter a “YES” in the column designated as “Console OK?”

Fill in Columns 2 & 3 of the Weekly MRI Quality Control Spreadsheet.

Center Frequency and Transmitter Gain

The Center Frequency and Transmitter Gain of the ACR T1 protocol must be documented on the QC Form.  The ACR T1 protocol should use the following parameters.

ACR T1 Imaging Parameters

Pulse SequenceSpin Echo
TR500 ms
TE20 ms
FOV25 cm
Number of Slices11
Slice Thickness5 mm
Slice Gap5 mm
NEX (Averages)1
Matrix256 x 256
Scan Time~ 2:10

The ACR T1 protocol should be used to scan the phantom in 11 slices.  The scan range should be placed right between the two 45⁰ wedges placed in the phantom.  See figure to the right.

Action Criteria: The Larmor Frequency is about 64 MHz for a 1.5T scanner and 128 MHz for a 3T scanner.  This means the action limit for 1.5T scanners is a week to week change of ± 128 Hz.  The action limit for 3T scanners is a week to week change of ± 256 Hz.  Recording the last 4 digits of the Center Frequency in Hz is fine.  For Transmit Gain, we typically set a baseline by taking an average after a series of 10 measurements and set action limits of ±20% from baseline.  You should consult with your medical physicist when setting the baseline values and action limits for the Center Frequency and Transmit Gain.

Fill in Columns 4 & 5 of the Weekly MRI Quality Control Spreadsheet.

Geometric Accuracy Measurements

Geometric Accuracy is measured using the Sagittal Localizer as well as Slice 5 from the ACR T1 series.  It’s important to set the window width and level the same way each time.  The ACR’s method for doing this is a little complicated, so we’re going to break this down.

Step 1:  Set the window width to 0 or 1.
Step 2: Adjust the window level until one half of the image is white and the other half is black.  It’s OK to estimate here. Note the window level setting.
Step 3:  Now adjust the window width to the same value.  We want the window width and window level to be equal.
Step 4: Finally, reduce the window level value by half. 

Step 2 - Half White / Half Black

Example: Bring your window width to 0.  Adjusting the window level until half the image is white and half is black you note the window level is at ~1400.  Now you adjust the window width to also be ~1400.  Finally, take you window level to ~700 and you’re ready to make your measurements!

Proceed with making geometric accuracy measurements on the image(s).  For the Sagittal Localizer image, you’ll make a measurement in the Head/Foot direction (top to bottom).  Then for Slice 5 on the ACR T1 protocol, you’ll make measurements in the Anterior/Posterior direction and in the Right/Left direction.

Sagittal Localizer Geometric Accuracy Measurements
Slice 5 Geometric Accuracy Measurements

Action Criteria: Your measurements should be within ± 2mm of their true values.

Fill in Columns 6, 7 & 8 of the Weekly MRI Quality Control Spreadsheet.

High Contrast Spatial Resolution

Now we’re ready to move on to High Contrast Spatial Resolution.  We’re going to simplify this and just call this resolution.  Resolution is measured using Slice 1 of the ACR T1 images series.  The resolution insert consists of three resolution targets with an upper-left (UL) and lower-right (LR) and share one hole in common at the corner where they meet.  The diameter of the left target is 1.1 mm, the center target is 1.0 mm, and the right target is 0.9 mm.

Resolution-Measurements-1-pbl1sq0yxgpgqyms9ib8faay06iwhdnq9hv176pzwg
High Contrast Spatial Resolution Targets & Hole Sizes

Zoom in on the image so that you can see the resolution targets.  Then adjust the window width and level until the holes in the resolution insert can best be seen.  The upper-left array is used to assess resolution in the horizontal direction.  To do this, look at the rows in the upper-left array to see if all four holes in any single row are distinguishable from one another.  The smallest target with an entire row as distinguishable should be recorded as the resolution for the upper-left (UL) array. 

Repeat the same steps for the lower-right array in the vertical direction by looking at the columns in the lower-right array to see if all four holes in any single column are distinguishable from one another.  The smallest target with an entire column as distinguishable should be recorded as the resolution for the lower-right (LR) array. 

So what exactly does distinguishable mean?  To be observed as distinguishable, the image intensity does not need to drop to zero between the holes; that would not be normal.  However, the window width and level setting should allow all four holes in at least one row (UL) or one column (LR) as recognizable points of brighter signal intensity than the spaces between them.  When the holes size is comparable to the resolution in the images, there is a tendency for groups of two or more holes in a row or column to blur together and appear as a single irregularly shaped spot of signal. In this case the holes in that row or column would be considered unresolved. 

Let’s look at an example…

High Contrast Spatial Resolution Example

In the example above we can see every row in the upper-left array and every column in the lower-right array for the 1.0 mm targets.  When we look at the 0.9 mm targets, we can distinguish 2 rows in the upper-left array and 2 columns in the lower-right array.  Because we only need to see at least one row and one column to call a target visualized, we would enter 0.9 mm into our spreadsheet for Columns 9 and 10.

Action Criteria: You should be able to visualize at least the 1.0 mm target.

Fill in Columns 9 & 10 of the Weekly MRI Quality Control Spreadsheet.

Low Contrast Detectability

Low Contrast Detectability (LCD) is evaluated in slices 8-11 of the ACR T1 series.  In each slice, the low-contrast objects appear as a row of small disks radiating from the center of the phantom like spokes on a wheel.  Each spoke is made up of 3 discs, and there are 10 spokes in each circle.  The contrast values increase as you go from slice 8 to slice 11.  The measurements for this test consists of counting the number of complete spokes seen in a designated axial slices.  Which slice is the designate slice?  The most appropriate slice for evaluation should be set by your medical physicist.  However, general guidance for determining the appropriate slice is to use the lowest contrast slice where some spokes are not visualized.  This is often Slice 8.

Display the slice to be scored using a window width and level setting for best visibility of the low contrast objects.  Count the number of spokes seen beginning with the 12 o’clock position and working clockwise.  The number of complete spokes where all three discs are discernible from background is the score for that slice.

Low Contrast Objects
Magnified Low Contrast Objects

Action Criteria: The action criteria for low contrast should be set by your medical physicist.

Artifact Evaluation

Artifact Evaluation should be performed on each slice of the ACR T1 series.  The window width and level should be adjusted so that a full range of pixel values can be observed in the image; the image should have varying levels of gray and should not be all black or all white.  When evaluating the phantom for artifacts, you should make sure

  • The phantom appears circular, not elliptical or otherwise distorted.
  • There are no ghost images of the phantom in the background or overlying the phantom image.
  • There are no streaks or artifactual bright or dark spots in the image.
  • There are no unusual or new features in the image.

Action Criteria: The images should be free of artifacts.  If you have artifacts in the image, you should contact your service engineer or medical physicist.

MRI Accreditation Program Visual Checklist

On a weekly basis, the MRI Visual Checklist should be completed to verify the MRI system patient bed transport, alignment and system indicator lights, RF room integrity, emergency cart, safety lights, signage, and monitors are present and working properly and are mechanically and electrically stable.

Documentation is performed on a separate Visual Checklist sheet.  You can download a copy here.

MRI Accreditation Program Visual Checklist

Each of the items listed in the visual checklist should pass or receive a checkmark.  Items not passing the visual checklist should be replaced or corrected immediately.  Items missing from the room should be replaced immediately.  Malfunctioning equipment should be reported to the MRI service engineer for repair or replacement as soon as possible.

Wrapping Up

If you’ve made it this far, congratulations!  You’ve successfully made it through all of the required steps for performing MRI Quality Control.  A couple of key takeaways

  • Perform MRI QC on a weekly basis
  • Follow the steps in this guide
  • Document your results

And that’s it.  You’re now well on your way to a well-executed quality control program and passing all of your ACR inspections like a breeze! 

Your medical physicist is a great resource for you when designing your MRI Quality Control Program.  You can also always reach out to us if you have questions or want more information on MRI Quality Control or want to see why you should partner with us.  We also offer Annual MRI Physics Testing and MRI Safety Audits.

Contact Us for a No Obligation Quote

253-254-6988
Request a Call Back