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DOI: 10.1148/rg.243035190
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RadioGraphics 2004;24:867-878
© RSNA, 2004

Imaging & Therapeutic Technology

MR Lymphangiography: Imaging Strategies to Optimize the Imaging of Lymph Nodes with Ferumoxtran-101

Mukesh G. Harisinghani, MD, W. Thomas Dixon, PhD, Mansi A. Saksena, MD, Elena Brachtel, MD, Daniel J. Blezek, PhD, Paritosh J. Dhawale, PhD, Maha Torabi, MD and Peter F. Hahn, MD, PhD

1 From the Departments of Radiology (M.G.H., M.A.S., M.T., P.F.H.) and Pathology (E.B.), Massachusetts General Hospital, 55 Fruit St, Boston, MA 02114; and General Electric Global Research, Niskayuna, NY (W.T.D., D.J.B., P.J.D.). Recipient of a Cum Laude award for an education exhibit at the 2002 RSNA scientific assembly. Received September 8, 2003; revision requested November 3 and received December 15; accepted December 23. Address correspondence to M.G.H. (e-mail: mharisinghani@partners.org).


   Abstract
Top
 Abstract
Introduction
 Imaging Technique
 Imaging Protocols
 Conclusions
 Appendix: Pulse Sequence...
 References
 
Detection of local or regional metastases to lymph nodes is clinically important in virtually any type of primary tumor. Current imaging techniques rely heavily on the size criterion for characterization of nodal disease. However, size can be an ineffective parameter for diagnosis of tumor spread to lymph nodes. Magnetic resonance (MR) imaging performed before and after administration of ferumoxtran-10 is a promising technique for characterization of lymph nodes in patients with various primary tumors. Normal homogeneous uptake of ferumoxtran-10 in nonmetastatic nodes shortens the T2 and T2*, turning these nodes dark, whereas malignant nodes lack uptake and remain hyperintense. To optimize acquisition strategies, the following factors should be considered: the timing of contrast material–enhanced imaging, the section thickness, the imaging plane, and the imaging parameters for T2*-weighted sequences. In addition, MR imaging with ferumoxtran-10 allows presurgical mapping of lymph nodes and quantitative estimation of T2*.

© RSNA, 2004

Index Terms: Contrast media, 99.12943 • Lymphatic system, MR, 99.12943 • Lymphatic system, neoplasms, 99.83 • Magnetic resonance (MR), contrast media, 99.12943


   Introduction
Top
 Abstract
 Introduction
Imaging Technique
 Imaging Protocols
 Conclusions
 Appendix: Pulse Sequence...
 References
 
The spread of primary tumor to regional and distant lymph nodes determines tumor staging, affects the choice of therapy, and allows prediction of patient outcome (1–3). All current cross-sectional imaging techniques (ultrasonography, computed tomography [CT], and magnetic resonance [MR] imaging) have a relatively low sensitivity in detecting nodal metastases primarily because detection relies on insensitive size criteria (4–7) (Figs 1, 2). Attempts to use the signal intensity at MR imaging for differentiating normal from metastatic lymph nodes have also proved unreliable (8–10).



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  		Figure 1.  Benign lymph node in a patient with prostate cancer. Axial contrast material-enhanced CT image shows an enlarged right obturator node (arrow). The node was interpreted as metastatic on the basis of the size criterion but proved to be benign at biopsy.

 


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  		Figure 2.  Malignant lymph node in a patient with renal cancer. Axial contrast-enhanced CT image shows a normal-sized right retrocaval node (arrow). The node was interpreted as benign on the basis of the size criterion but proved to be malignant at surgery.

 
Ferumoxtran-10 (Combidex [Advanced Magnetics, Cambridge, Mass]; also known as Sinerem, AMI-7227, AMI-227, and BMS 180549) is a reticuloendothelial system–targeted MR imaging contrast agent consisting of ultrasmall superparamagnetic iron oxide particles, which was specifically developed for MR lymphangiography (11–15) and to improve the detection of minimal nodal metastases. These ultrasmall superparamagnetic nanoparticles are composed of an iron oxide crystalline core of 4.3–6.0 nm covered by low-molecular-weight dextran. The T1 and T2 relaxivities of these nanoparticles are 2.3 x 104 and 5.3 x 104 mol–1 sec–1 (20 MHz, 39°C), respectively, in 0.5% agar (16).

After intravenous injection of the recommended dose of 2.6 mg of iron per kilogram of body weight, ferumoxtran-10 particles are transported into the interstitial space and subsequently via lymph vessels into the lymph nodes (16). Once within normally functioning nodes, the iron particles are phagocytosed by the macrophages, reducing the signal intensity of normal lymph nodes in which they accumulate due to the susceptibility effects of iron oxide reducing T2*. In areas of lymph nodes replaced by malignant cells, there is absence of macrophage activity and hence lack of ferumoxtran-10 uptake (Fig 3). Thus, postferumoxtran MR imaging allows identification of metastatic areas within the lymph nodes independently of the lymph node size.



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  		Figure 3a.  Pathologically proved benign and metastatic pelvic lymph nodes in a patient with bladder cancer. (a) Axial T2*-weighted gradient-echo MR image shows bilateral hyperintense external iliac nodes (arrows), which were characterized as metastatic on the basis of the size criterion. (b) Axial MR image obtained 24 hours after administration of ferumoxtran-10 shows a homogeneous decrease in the signal intensity of the right external iliac node (straight arrow), a finding indicative of a benign origin. However, the left external iliac node (curved arrow), which is enlarged, demonstrates a peripheral drop in signal intensity with preserved central high signal intensity, findings indicative of metastatic infiltration. These findings were confirmed at surgery.

 


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  		Figure 3b.  Pathologically proved benign and metastatic pelvic lymph nodes in a patient with bladder cancer. (a) Axial T2*-weighted gradient-echo MR image shows bilateral hyperintense external iliac nodes (arrows), which were characterized as metastatic on the basis of the size criterion. (b) Axial MR image obtained 24 hours after administration of ferumoxtran-10 shows a homogeneous decrease in the signal intensity of the right external iliac node (straight arrow), a finding indicative of a benign origin. However, the left external iliac node (curved arrow), which is enlarged, demonstrates a peripheral drop in signal intensity with preserved central high signal intensity, findings indicative of metastatic infiltration. These findings were confirmed at surgery.

 
Several studies have demonstrated enhanced sensitivity and specificity for lymph node evaluation after ferumoxtran-10 administration, for pelvic, head and neck, and chest malignancies (11,16–30). Ferumoxtran-10 is clinically well tolerated after intravenous administration. In a recent publication on the comprehensive phase III efficacy and safety data, Anzai et al (31) reported the overall prevalence of adverse events to be 28% in 152 patients. The most frequently reported adverse events were headache, back pain, vasodilatation, and urticaria, each of which occurred in 6% of patients. None of the adverse events were serious, with most being mild or moderate in severity and of short duration.

The purpose of this article is to describe the acquisition strategies for optimizing the information from lymph nodes following the administration of ferumoxtran-10.


   Imaging Technique
Top
 Abstract
 Introduction
 Imaging Technique
Imaging Protocols
 Conclusions
 Appendix: Pulse Sequence...
 References
 
Imaging with ferumoxtran-10 involves two-dimensional (2D) axial T1-weighted gradient-echo, 2D axial T2-weighted fast spin-echo, and 2D axial T2*-weighted gradient-echo sequences before and 24 hours after the administration of ferumoxtran-10 (Fig 4). Although the default plane for imaging is axial, this can be altered based on the area of interest being imaged. A three-dimensional (3D) T1-weighted gradient-echo sequence may also be added for presurgical mapping of nodes.



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  		Figure 4a.  Sequences for MR imaging with ferumoxtran-10. Axial T1-weighted gradient-echo (a), T2-weighted fast spin-echo (b), and T2*-weighted gradient-echo (c) MR images, obtained after administration of ferumoxtran-10, show a benign left inguinal lymph node (arrow). The node demonstrates homogeneous uptake of ferumoxtran-10 on the T2*-weighted gradient-echo image (c).

 


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  		Figure 4b.  Sequences for MR imaging with ferumoxtran-10. Axial T1-weighted gradient-echo (a), T2-weighted fast spin-echo (b), and T2*-weighted gradient-echo (c) MR images, obtained after administration of ferumoxtran-10, show a benign left inguinal lymph node (arrow). The node demonstrates homogeneous uptake of ferumoxtran-10 on the T2*-weighted gradient-echo image (c).

 


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  		Figure 4c.  Sequences for MR imaging with ferumoxtran-10. Axial T1-weighted gradient-echo (a), T2-weighted fast spin-echo (b), and T2*-weighted gradient-echo (c) MR images, obtained after administration of ferumoxtran-10, show a benign left inguinal lymph node (arrow). The node demonstrates homogeneous uptake of ferumoxtran-10 on the T2*-weighted gradient-echo image (c).

 
The T1- and T2-weighted sequences are useful for anatomic localization and detection of nodes. In addition, the T1-weighted sequences help identify the fatty hilum within the node, which may mimic nodal metastases on the T2- and T2*-weighted images (Fig 5). The T2*-weighted gradient-echo sequences are the key sequences for displaying ferumoxtran-10 uptake. A general outline of pulse sequence parameters is listed in the Appendix.



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  		Figure 5a.  Fatty hilum of a lymph node at ferumoxtran-10 imaging of the pelvis. (a) Axial T2*-weighted gradient-echo MR image, obtained 24 hours after administration of ferumoxtran-10, shows a right inguinal node with peripheral decreased signal intensity (black arrow) and central high signal intensity (white arrow), an appearance that may be misinterpreted as representing a metastatic deposit. (b) Axial T1-weighted gradient-echo MR image shows that the central area of the node has high signal intensity (top white arrow), which indicates that this area represents the normal fatty hilum of the node. Note the enhancement of the femoral vessels (bottom white arrow) adjacent to the node, an appearance caused by the effect of ferumoxtran-10 on T1. Black arrow = peripheral decreased signal intensity.

 


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  		Figure 5b.  Fatty hilum of a lymph node at ferumoxtran-10 imaging of the pelvis. (a) Axial T2*-weighted gradient-echo MR image, obtained 24 hours after administration of ferumoxtran-10, shows a right inguinal node with peripheral decreased signal intensity (black arrow) and central high signal intensity (white arrow), an appearance that may be misinterpreted as representing a metastatic deposit. (b) Axial T1-weighted gradient-echo MR image shows that the central area of the node has high signal intensity (top white arrow), which indicates that this area represents the normal fatty hilum of the node. Note the enhancement of the femoral vessels (bottom white arrow) adjacent to the node, an appearance caused by the effect of ferumoxtran-10 on T1. Black arrow = peripheral decreased signal intensity.

 

   Imaging Protocols
Top
 Abstract
 Introduction
 Imaging Technique
 Imaging Protocols
Conclusions
 Appendix: Pulse Sequence...
 References
 
Timing of Contrast-enhanced Imaging
The optimal time for the postcontrast imaging with ferumoxtran-10 is 24–36 hours, as established by early animal and human studies (11,32). This time lag before performing the postcontrast imaging is essential to allow sufficient extraction of ferumoxtran-10 by normal functioning macrophages within the nodes. If imaging is performed prematurely, the lack of sufficient nodal uptake within benign nodes may lead to erroneous characterization as malignant nodes (Fig 6).



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  		Figure 6a.  Benign pelvic lymph node in a patient with bladder cancer. (a) Unenhanced axial T2*-weighted MR image shows a hyperintense right external iliac node (arrow). (b) Axial MR image obtained 8 hours after administration of ferumoxtran-10 shows a heterogeneous drop in signal intensity (arrow), which may be interpreted as malignant infiltration. (c) Delayed axial MR image obtained at the optimal 24-hour interval shows a homogeneous drop in signal intensity within the node (arrow). This finding indicates benignity, which was confirmed at surgery.

 


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  		Figure 6b.  Benign pelvic lymph node in a patient with bladder cancer. (a) Unenhanced axial T2*-weighted MR image shows a hyperintense right external iliac node (arrow). (b) Axial MR image obtained 8 hours after administration of ferumoxtran-10 shows a heterogeneous drop in signal intensity (arrow), which may be interpreted as malignant infiltration. (c) Delayed axial MR image obtained at the optimal 24-hour interval shows a homogeneous drop in signal intensity within the node (arrow). This finding indicates benignity, which was confirmed at surgery.

 


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  		Figure 6c.  Benign pelvic lymph node in a patient with bladder cancer. (a) Unenhanced axial T2*-weighted MR image shows a hyperintense right external iliac node (arrow). (b) Axial MR image obtained 8 hours after administration of ferumoxtran-10 shows a heterogeneous drop in signal intensity (arrow), which may be interpreted as malignant infiltration. (c) Delayed axial MR image obtained at the optimal 24-hour interval shows a homogeneous drop in signal intensity within the node (arrow). This finding indicates benignity, which was confirmed at surgery.

 
Section Thickness
Accurate characterization of nodes with ferumoxtran-10 requires high spatial resolution imaging. One of the important factors affecting the resolution is section thickness. Imaging with thinner sections reduces partial volume artifacts and allows detection of small metastatic foci within the nodes (Fig 7). Moreover, thinner sections also allow better delineation of nodal anatomy with fewer false positives due to hilar fat (Fig 8).



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  		Figure 7a.  Benign and malignant axillary lymph nodes in a patient with breast cancer. Axial MR images, obtained with a 3-mm section thickness before (a) and after (b) administration of ferumoxtran-10, show a benign axillary node (black arrow) and an adjacent malignant node (white arrow). On the contrast-enhanced image (b), the benign node demonstrates a homogeneous drop in signal intensity (black arrow), whereas the malignant node remains hyperintense (white arrow).

 


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  		Figure 7b.  Benign and malignant axillary lymph nodes in a patient with breast cancer. Axial MR images, obtained with a 3-mm section thickness before (a) and after (b) administration of ferumoxtran-10, show a benign axillary node (black arrow) and an adjacent malignant node (white arrow). On the contrast-enhanced image (b), the benign node demonstrates a homogeneous drop in signal intensity (black arrow), whereas the malignant node remains hyperintense (white arrow).

 


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  		Figure 8a.  Pathologically proved benign lymph node in a patient with prostate cancer. Axial MR images, obtained with a 3-mm section thickness before (a) and after (b) administration of ferumoxtran-10, show a node (circle) with peripheral uptake of contrast material and a prominent central fatty hilum.

 


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  		Figure 8b.  Pathologically proved benign lymph node in a patient with prostate cancer. Axial MR images, obtained with a 3-mm section thickness before (a) and after (b) administration of ferumoxtran-10, show a node (circle) with peripheral uptake of contrast material and a prominent central fatty hilum.

 
Imaging Plane
For most imaging of lymph nodes, thin-section axial images suffice. However, alternate imaging planes may be needed, depending on the area of interest being imaged. For example, imaging of lymph nodes in the axilla for breast cancer and in the pelvis for prostate cancer requires alternate imaging planes.

Imaging of the axilla for nodal metastases from breast cancer requires imaging in an oblique sagittal plane, as this provides anatomic localization of the lymph nodes in relation to the primary tumor, thereby helping the surgeon during surgical dissection (Fig 9). Similarly, imaging the pelvis in an oblique coronal plane (the "obturator plane") provides the location of the nodes in relation to the obturator nerve during surgery. The urologist typically resects nodes anterior to the obturator nerve and does not dissect further without evidence of nodal metastases posterior to the nerve.



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  		Figure 9.  Use of an alternate imaging plane. Oblique sagittal T2-weighted MR image of the axilla shows the anatomic location of a metastatic lymph node (black arrow) in relation to the primary tumor (white arrow).

 
Optimizing Imaging Parameters for T2*-weighted Sequences
Ferumoxtran-10 shortens T1 and T2*. The shortening of T1 increases signal intensity, whereas shortening T2* decreases signal intensity. Thus, imaging detection of ferumoxtran-10 can be based on pulse sequences sensitive to either its T1 effects or its T2* effects, but not on both. Indeed, a balanced sequence can obscure the presence of ferumoxtran-10 in a lymph node. As the primary concern is lymph node characterization and estimating nodal tumor burden, the choice is to enhance T2* weighting while limiting the influence of T1. The following is an outline for the control of T1 weighting in multisection gradient-echo imaging, thereby enhancing the desired T2* effect.

Pixel intensity is proportional to magnetization along the field (Mz), which depends on T1. Mz can be calculated by using the following equation:


where the relaxation rate r = 1/T1, TR is the repetition time, and FA is the flip angle (the angular deflection of magnetization caused by a radiofrequency pulse) (33). Qualitatively, the relation expressed by Equation (1) is referred to as the T1 weighting. Figure 10 and the Table show the effect of TR and flip angle on T1 weighting. As seen in Figure 10, relaxation increases Mz, so the curves go up to the right; this effect is dependent nonlinearly on both TR and cos(FA).



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  		Figure 10.  Mz versus 1/T1. This relationship, which is called the T1 weighting, depends on the TR and flip angle. Traces a-d are the result of the TR-flip angle combinations in the Table. They show that raising the TR from 1/8 to 3/8 seconds (from a to b) changes the T1 weighting greatly. Changing the flip angle from 20° to 35° (from a to c) does the same. However, changing both the TR and the flip angle (from a to d) has almost no effect on the T1 weighting.

 

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  		Relationship between TR, Flip Angle, and T1 Weighting

 
A long TR or small flip angle keeps the T1 effects from masking the T2* effect for imaging of lymph nodes. The goal of setting up the T2*-weighted gradient-echo sequence is to choose, without trial and error, a TR and flip angle to optimize signal-to-noise ratio (SNR), meet a T1-weighting goal, and waste no imaging time. The effective TR (TReff) of a pulse sequence, defined by Equation (2), helps achieve this:


A sequence with any TR and flip angle will have almost exactly the same T1 weighting as a sequence with a 90° flip angle and TR = TReff. TReff describes the T1 weighting of an acquisition and depends on its TR and its flip angle. Two or more combinations of TR and flip angle can give nearly identical dependences of Mz on T1 and therefore nearly identical T1 weighting in images. Curves a and d in Figure 10 have the same TReff and are examples. If longitudinal magnetization, Mz, is the same for several TR–flip angle combinations, then certainly the combination with a flip angle closest to 90° will provide the greatest transverse magnetization, signal, and SNR. This concept lies behind the following new procedure for acquisition setup.

Setting up an acquisition has three steps: (a) Find the longest TR that wastes no time; (b) find the TReff of a reference acquisition that meets the T1-weighting goal; and (c) with TR and TReff known, find the optimal flip angle. When these principles are used, the steps required to optimize T2* weighting for ferumoxtran-10 imaging are as follows:

1. Find the longest TR that is efficient in the sense that the imager is constantly busy (Fig 11). When n sections are imaged, a TR of n times the minimum TR that TE and hardware constraints allow fulfills this requirement. This TR is long enough that the imager will collect data from all sections at once rather than finishing some sections before starting others. Operator tools to determine this minimum allowed TR and to set up efficient acquisitions differ from imager to imager.



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  		Figure 11.  Efficient acquisition packing. The time required to excite a section and then observe it can be called TRmin. (TRmin is generally somewhat longer than the TE.) Diagram shows that setting TR to 3 · TRmin allows collection of three sections at once, whereas a TR of 9 · TRmin allows collection of nine sections at once. Both choices keep the imager busy and produce the same number of images per minute. Imaging nine sections in groups of three with a TR of 3 · TRmin is equally efficient. However, imaging four sections with a TR of 3 · TRmin leaves idle time, as would imaging any other number of sections not divisible by 3.

 
2. Find the TReff of the reference acquisition by using Equation (2). The TR and flip angle on the right side of the equation are those of the reference acquisition.

3. With TR and TReff known, find the flip angle. Rearranging Equation (2) gives the flip angle of the new acquisition:


In summary, TE and the number of sections set a minimum imaging time. Imaging extra sections requires extra time. Given that, the preceding procedure was designed to make good use of this time, increasing SNR to the maximum possible extent while duplicating the T1 weighting of a previous, lower-coverage reference examination that had satisfactory T1 weighting.

Figure 12 shows the clinical use of these principles, with a section from a five-section sequence suitable for breath holding compared to the same section obtained as part of a 70-section acquisition. Here, the increase in coverage and potential increase in SNR were so large that we elected not to maximize SNR. We used a slightly smaller flip angle than our procedure directed, increasing TReff somewhat to reduce unwanted T1 weighting. Although this parameter choice that improved the contrast did not raise SNR as much as possible, it still more than doubled SNR. The five- and the 70-section protocols had the same acquisition time per section. This example illustrates that TR and flip angle can and should be changed whenever the number of sections needs to be changed, even when the same contrast is desired.



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  		Figure 12a.  Optimization of imaging parameters. Axial T2*-weighted MR imaging of the pelvis was performed after administration of ferumoxtran-10. (a) Image obtained before technique optimization (TR = 250 msec, TE = 24 msec, flip angle = 17°, two signals acquired). (b) Image obtained after technique optimization (TR = 2,100 msec, TE = 24 msec, flip angle = 70°, two signals acquired). Note the higher SNR and the better demonstration of the pelvic anatomy. Arrow = benign right obturator node.

 


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  		Figure 12b.  Optimization of imaging parameters. Axial T2*-weighted MR imaging of the pelvis was performed after administration of ferumoxtran-10. (a) Image obtained before technique optimization (TR = 250 msec, TE = 24 msec, flip angle = 17°, two signals acquired). (b) Image obtained after technique optimization (TR = 2,100 msec, TE = 24 msec, flip angle = 70°, two signals acquired). Note the higher SNR and the better demonstration of the pelvic anatomy. Arrow = benign right obturator node.

 
Optimal TE for T2*-weighted Sequence
Because imaging of normal lymph nodes with ferumoxtran-10 relies on signal intensity drop from susceptibility, choosing an optimal TE value is important for making the correct diagnosis. Just as imaging earlier than 24 hours may result in erroneous interpretation, imaging with a short TE may provide inadequate signal intensity drop, resulting in erroneous interpretation. Figure 13 shows the need to use an adequately long TE for ferumoxtran-10 to decrease the signal intensity enough in order to provide adequate contrast in a benign lymph node.



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  		Figure 13a.  Optimal TE for imaging with ferumoxtran-10. Axial T2*-weighted MR imaging of the pelvis was performed in a patient with prostate cancer after administration of ferumoxtran-10. (a) Image obtained with a TE of 14 msec shows a left external iliac node with central heterogeneity (arrow), a finding that may be interpreted as representing metastatic infiltration. (b) Image obtained with a TE of 24 msec at the same time as a shows a more homogeneous drop in signal intensity (arrow). This finding indicates benignity, which was proved at pathologic analysis.

 


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  		Figure 13b.  Optimal TE for imaging with ferumoxtran-10. Axial T2*-weighted MR imaging of the pelvis was performed in a patient with prostate cancer after administration of ferumoxtran-10. (a) Image obtained with a TE of 14 msec shows a left external iliac node with central heterogeneity (arrow), a finding that may be interpreted as representing metastatic infiltration. (b) Image obtained with a TE of 24 msec at the same time as a shows a more homogeneous drop in signal intensity (arrow). This finding indicates benignity, which was proved at pathologic analysis.

 
Presurgical Mapping of Nodes
As stated earlier, a postcontrast 3D T1-weighted imaging sequence with a short TE and flow compensation can be performed, exploiting the T1 properties of ferumoxtran-10. This lays out the vascular anatomy on which the lymph nodes can be plotted for precise surgical mapping and resection (Fig 14).



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  		Figure 14.  Mapping of lymph nodes in a patient with prostate cancer. Surface-rendered 3D MR image shows the iliac vessels, distal aorta, and inferior vena cava, which are enhanced due to the effect of ferumoxtran-10 on T1. Malignant nodes are coded in red (arrows), thus showing their relationships to the major vessels.

 
Quantitative Estimation of T2*
The qualitative assessment of signal intensity changes within lymph nodes after ferumoxtran-10 administration allows nodal characterization and detection of metastatic disease. The accuracy of the qualitative assessment and detection of metastatic infiltration is based on the lack of ferumoxtran-10 uptake within areas of metastases. However, minimal tumor infiltration within small nodes may be difficult to appreciate qualitatively and hence quantitative estimation of ferumoxtran-10 uptake may aid in characterizing these infiltrated small nodes. Performing a dual-TE T2*-weighted gradient-echo sequence allows indirect estimation of ferumoxtran-10 uptake by calculating T2* within the lymph nodes (Fig 15). Studies are under way to determine if there is a quantitative T2* cutoff value that allows robust differentiation between benign and malignant lymph nodes.



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  		Figure 15a.  Quantitative estimation of T2* in a benign lymph node. The T2* value was computed with a customized semiautomated segmentation algorithm. Axial dual-TE T2*-weighted gradient-echo MR images, obtained before (a) and after (b) administration of ferumoxtran-10, show a benign node (arrow), which is outlined by a region of interest. The node demonstrates a considerable drop in its T2* value on the contrast-enhanced image (b).

 


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  		Figure 15b.  Quantitative estimation of T2* in a benign lymph node. The T2* value was computed with a customized semiautomated segmentation algorithm. Axial dual-TE T2*-weighted gradient-echo MR images, obtained before (a) and after (b) administration of ferumoxtran-10, show a benign node (arrow), which is outlined by a region of interest. The node demonstrates a considerable drop in its T2* value on the contrast-enhanced image (b).

 

   Conclusions
Top
 Abstract
 Introduction
 Imaging Technique
 Imaging Protocols
 Conclusions
Appendix: Pulse Sequence...
 References
 
Small lymph nodes are the critical targets for cancer staging. Use of the optimization tools presented in this article in conjunction with ferumoxtran-10 will enhance the accuracy of MR imaging for staging cancer in small nodes.


   Appendix: Pulse Sequence Parameters
Top
 Abstract
 Introduction
 Imaging Technique
 Imaging Protocols
 Conclusions
 Appendix: Pulse Sequence...
References
 
Pulse sequence parameters for the 1.5-T Horizon imager (GE Medical Systems, Milwaukee, Wis) are as follows:

1. T2-weighted fast spin-echo sequence: repetition time (TR) = 4,500–5,500 msec, echo time (TE) = 80–100 msec, flip angle = 90°, three signals acquired, section thickness = 3 mm, gap = 0 mm, 256 x 256 matrix, and field of view = 22–30 cm.

2. T2*-weighted gradient-echo sequence: TR = 300–400 msec, TE = 24 msec, flip angle = 20°, two signals acquired, section thickness = 3 mm, gap = 0 mm, 160 x 256 matrix, and field of view = 22–30 cm.

3. 2D T1-weighted gradient-echo sequence: TR = 175 msec, TE = 1.8 msec, flip angle = 80°, two signals acquired, section thickness = 4 mm, gap = 0 mm, 128 x 256 matrix, and field of view = 22–30 cm.

4. 3D T1-weighted gradient-echo sequence: TR = 4.5–5.5 msec, TE = 1.4 msec, flip angle = 15°, two signals acquired, section thickness = 5 mm, gap = 0 mm, 256 x 256 matrix, and field of view = 24–32 cm.

Pulse sequence parameters for the 1.5-T Magnetom Vision imager (Siemens Medical Solutions, Erlangen, Germany) are as follows:

1. T2-weighted turbo spin-echo sequence: TR = 4,000–4,500 msec, TE = 80–90 msec, flip angle = 90°, two signals acquired, section thickness = 3 mm, gap = 0 mm, 256 x 256 matrix, and field of view = 22–30 cm.

2. High spatial resolution 3D T1-weighted magnetization-prepared rapid gradient-echo (MP-RAGE) sequence: TR = 11–13 msec, TE = 4–5 msec, flip angle = 8°, two signals acquired, section thickness = 1.4 mm, gap = 0 mm, 256 x 256 matrix, and field of view = 22–30 cm.

3. 2D T2*-weighted fast low-angle shot (FLASH) or T2*-weighted multiecho data image combination (MEDIC) sequences: TR = 800–1,500 msec, TE = 25.4 msec, flip angle = 30°, two signals acquired, and section thickness = 3 mm. Images are obtained in the axial and oblique plane parallel to the iliac vessels (the obturator plane).


   Footnotes
 
Abbreviations: SNR = signal-to-noise ratio, TE = echo time, 3D = three-dimensional, TR = repetition time, 2D = two-dimensional


   References
Top
 Abstract
 Introduction
 Imaging Technique
 Imaging Protocols
 Conclusions
 Appendix: Pulse Sequence...
 References
 

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