Name: measurement of tumor t2* relaxation times after iron oxide nanoparticle administration
Uploaded: 2023-05-19T13:10:00
Description: Watch this Scientific Journal Video about Measurement of Tumor T2* Relaxation Times after Iron Oxide Nanoparticle Administration at JoVE.com

This work was in part supported by a grant from the National Cancer Institute, grant number U24CA264298. We thank Dawn Holley, Kim Halbert, and Mehdi Khalighi from the PET/MRI Metabolic Service Center for their assistance with the acquisition of PET/MRI scans at the Lucas Research Center at Stanford. We thank the members of the Daldrup-Link lab for valuable input and discussions regarding this project.

This protocol has been generated for a prospective clinical trial and co-clinical research. The study was compliant with the Health Insurance Portability and Accountability Act (HIPAA) and approved by the Stanford University institutional review board (IRB). All patients or their legally authorized representative signed a written informed consent, and all children between 7 and 18 years of age signed an assent form.
1. Installing and starting the T2 Fit Map plugin
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Our protocol allows us to measure tumor T2* relaxation times based on multi-echo gradient-echo sequences, an external software, and a plugin for creating T2* maps. The critical steps within the protocol are the inclusion of the multi-echo gradient-echo sequence with very short TEs into the scanning protocol, and the monoexponential fit of the multi-echo gradient-echo images using external software. It is important to arrange the input multi-echo gradient-echo images according to their acquisition times. This can be achie...

Noninvasive quantification of tumor T2* relaxation times in various tissues of the body with magnetic resonance imaging (MRI) is widely established1. The rationale for this article is to provide a protocol for the measurement of tumor T2* relaxation times which is independent of scanner software like Osirix2. This will allow uniform analyses of imaging data from different centers, different scanners, and different vendors. Indeed, thousands of users could potentially use the same approach, thereby increasing the standardization of tumor T2* measurements. T2* measurements are used for different purposes by neuroradiologists, cardiac imaging experts, and abdominal imaging experts, among others. MRI pulse sequences for measurements of tissue T2* relaxation times have been applied and optimized for the assessment of intracranial bleeds3, hepatic iron content1,4, and cardiac iron content5,6, among others. Other investigators have used T2* measurements to generate quantitative estimates of iron oxide nanoparticle accumulations in malignant tumors7,8. However, many of these previous approaches utilized institutional software or specific scanner software, which would be limited to use at a specific institution or for processing data obtained on a specific scanner. Here, we describe a universally applicable approach for generating tumor T2* maps and tumor T2* relaxation times based on preclinical or clinical MRI data from any scanner that can generate multi-echo gradient echo images. The required gradient echo sequence should have very short first echo times and close inter-echo spacing9,10. The multi-echo gradient echo images are then fed into the external software, tumor T2* maps are calculated, and tumor T2* relaxation times are measured. The T2 Fit Map plugin in the external models&#39; T2* decay curves as a monoexponential fit to S(t) = Soe-t/T2* 11 where S(t) represents the signal or process value at a given time t; S0 is the initial value of the signal or process at t = 0; t denotes time; T2*, also known as the apparent transverse relaxation time, characterizes the decay rate of the signal or process; and e is the base of the natural logarithm (approximately equal to 2.71828). The equation describes an exponential decay, where the signal or process decreases over time as a function of the decay rate T2*. The larger the value of T2*, the slower the decay rate, and vice versa. The same software can also be used to input multi-echo spin echo images and generate tumor T2 values by fitting the T2 decay curve to S(t) = Soe-t/T2. The curve fitting was performed using external software, without incorporating a constant offset. Both decay curves exhibit single exponential behavior, with T2* demonstrating a shorter duration compared to T2.
In patients with hemosiderosis and hemochromatosis, the quantification of liver iron content by tissue biopsy is the gold standard, whereas noninvasive MR imaging is the point of care for establishing baseline values and monitoring changes over time noninvasively12,13. While generating T2* maps for liver iron quantification is well established4, there is no standardized protocol to measure tumor T2* relaxation times. While T2* maps can also be generated by scanner software, it is limited to a specific scanner and vendor. In the field of oncology, serial imaging studies of a given patient often occur on different scanners, and multicenter MRI data are acquired based on imaging studies from different scanners and different vendors. In addition, co-clinical imaging research is being increasingly implemented and requires the comparison of MRI data of patients and mouse models that simulate their tumor. The purpose of this protocol is to provide a protocol for the measurement of tumor T2* relaxation times that are independent of the scanner software. This will allow uniform analysis of imaging data from different centers and different scanners. Indeed, thousands of users could potentially use the same approach, thereby increasing the standardization and reproducibility of tumor T2* measurements. Our protocol utilizes external software, which can be downloaded from the internet. Multi-echo gradient echo images are fed into the software and fit to a formula for monoexponential decay to generate a T2* map, on which tumor T2* relaxation times can be measured using operator-defined regions of interest (ROIs)5. Iron oxide nanoparticles can be infused at different doses14, In our study, the patient received a Ferumoxytol injection (30 mg/mL) containing 510 mg of elemental iron in a 17 mL volume, at a dosage of 5 mg elemental iron per kg body weight. Subsequently multi-echo gradient echo sequences were obtained15 using set sequence parameters for data acquisition.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>OsiriX</td>
			<td>Pixmeo SARL</td>
			<td></td>
			<td>https://www.osirix-viewer.com/</td>
		</tr>
		<tr>
			<td>3T GE MR 750</td>
			<td>GE Healthcare, Chicago, IL</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>FERAHEME (ferumoxytol injection)</td>
			<td>AMAG Pharmaceuticals, Inc. 1100 Winter Street Waltham, MA 02451</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

measurement of tumor t2* relaxation times after iron oxide nanoparticle administration

T2* relaxometry is one of the established methods to measure the effect of superparamagnetic iron oxide nanoparticles on tumor tissues with magnetic resonance imaging (MRI). Iron oxide nanoparticles shorten the T1, T2, and T2* relaxation times of tumors. While the T1 effect is variable based on the size and composition of the nanoparticles, the T2 and T2* effects are usually predominant, and T2* measurements are the most time-efficient in a clinical context. Here, we present our approach to measuring tumor T2* relaxation times, using multi-echo gradient echo sequences, external software, and a standardized protocol for creating a T2* map with scanner-independent software. This facilitates the comparison of imaging data from different clinical scanners, different vendors, and co-clinical research work (i.e., tumor T2* data obtained in mouse models and patients). Once the software is installed, the T2 Fit Map plugin needs to be installed from the plugin manager. This protocol provides step-by-step procedural details, from importing the multi-echo gradient echo sequences into the software, to creating color-coded T2* maps and measuring tumor T2* relaxation times. The protocol can be applied to solid tumors in any body part and has been validated based on preclinical imaging data and clinical data in patients. This could facilitate tumor T2* measurements for multi-center clinical trials and improve the standardization and reproducibility of tumor T2* measurements in co-clinical and multi-center data analyses.

<img alt="Figure 10" class="xfigimg" src="/files/ftp_upload/64773/64773fig10.jpg" /> 
Figure 10: The T2* map with an ROI overlaid on the metastatic osteosarcoma lesion which shows the mean and standard deviation T2* value. <a href="https://www.jove.com/files/ftp_upload/64773/64773fig10large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<p class="jove_content biglegend" fo:keep-together....

Watch this Scientific Journal Video about Measurement of Tumor T2* Relaxation Times after Iron Oxide Nanoparticle Administration at JoVE.com

Measurement of Tumor T2* Relaxation Times after Iron Oxide Nanoparticle Administration

We present a standardized protocol for the quantification of T2* relaxation times of tumors using external software. Multi-echo gradient echo images are acquired and fed into the software to create tumor T2* maps and measure tumor T2* relaxation times.

T2* relaxometry is one of the established methods to measure the effect of superparamagnetic iron oxide nanoparticles on tumor tissues with magnetic ...

Our protocol enables standardized tumor T2*measurements across various scanners, manufacturers, and institutions. This protocol enables quality assurance improvement and broad clinical ability without requiring programming language. The main advantage of this technique is the ability to facilitate reliable and consistent tumor T2*measurements across various MRI scanners.Moreover, it offers an accessible and user-friendly approach, lowering the barriers of adoption. NOIs might struggle with proper sequence setup and ROI selection. The advice is to follow the protocol steps, ensure correct T arrangement and practice ROI drawing for accurate T2*map generation and fitting.Begin by starting the OsiriX software to install the T2 Fit Map Plugin. Click the Plugins button on the menu bar, then select Plugins Manager from the dropdown menu. Once the Plugin Manager is loaded, select T2 Fit Map from the available plugins.Click Download Install. Then close the Plugin Manager. Once the software is restarted, load the multi echo gradient deco sequence images as DICOM files into the software.Change the mouse button function to draw a region of interest or ROI. Then from the dropdown menu, select Oval or Closed Polygon or the desired shape and draw ROIs in the required images with different echo times. Select the ROIs from the images with different echo times for which the T2*map is required.From the dropdown menu, click the Plugins button, select Image Filters, and then select T2 Fit Map. Once T2 Fit Map is clicked, a dialogue box will open. Then click on Generate Map.To define the mask ROI on an image series outside the data, open the desired series and select a slice. From the ROI dropdown menu, select Grow Region and the 3D Growing Region radio button. In the Algorithm dropdown menu select Threshold Set the lower and upper thresholds to 0 and X percent of the contralateral muscle signal respectively.Name the ROI as desired. Then click on the image to place a seed for ROI growing and click Compute. In the ROI menu, select Save All ROIs of this Series.Next, open the dataset in the 4D viewer. After ensuring that the ROIs are in the first 3D volume, from the ROI menu, select Import ROI(s)Apply mask to map the data by selecting Set Pixel Values To.Then select Apply to ROIs with same name. Check the Propagate to 4D series box, set pixels that are Inside ROIs and set To this new value as zero.This study shows quantification of T2*relaxation time in a patient with metastatic osteosarcoma. A fitting curve is generated with minimum, mean, and maximum T2*values for the selected ROIs with various echo times for this patient. The color-encoded T2*maps were merged with a contrast-enhanced T1-weighted gradient deco image for anatomical orientation.It is important to arrange the input multi echo gradient deco images according to their acquisition times. This can be achieved by sorting the imaging data series by acquisition time in the external software under preferences database dropdown menu. Our protocol has significantly enhanced repeatability and reproducibility, providing consistent T2*relaxation times across diverse cancer studies.

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