This application tip document updates information originally provided in Application tips for prostate imaging, adding the dual coil option, 16-channel SENSE XL Torso and 32-channel SENSE Torso/Cardiac coils. Additonally, it provides workflow for coil and patient positioning.
Prostate imaging continues to be an important application for MRI especially in light of the data (2005) from the United States Center for Disease Control that places prostate cancer as the number one occurring cancer in males of all races in the United States.
Previously, the coil of choice for imaging at 1.5T was typically an endo cavity coil. This allowed placing the coil close to the prostate providing higher signal-to-noise ratio (SNR) than was possible with surface coils at the time. This additional SNR afforded the user the opportunity to obtain higher resolution imaging than they could with a surface coil. The small size of this coil however had the disadvantage of reduced signal penetration to the anatomy furthest from the coil resulting in poor or no visualization of structures located in this area of the Field of View (FOV). Changes in the Philips MRI system that allow the combination of certain coils has made it possible to fill in these areas of decreased signal by adding the 5-channel SENSE Cardiac coil.
Additionally changes in surface coil design have provided better SNR allowing the 3.0T user to take a non-invasive approach and image the prostate with similar resolution as obtained at 1.5T with an endo/cardiac combination.
While high resolution anatomic imaging of the prostate is now possible without the need for a endo coil, increasing interest in the use of proton spectroscopy and higher resolution imaging for staging has proved the advantage of again adding the endo coil in imaging of this organ at 3.0T.
This document will provide the user with some basics for imaging of the prostate.
The following table provides recommended coil/coil combinations for obtaining high quality anatomic imaging of the prostate at the respective field strengths.
SENSE Cardiac/Endo coil*?+
SENSE Torso coil
SENSE Cardiac coil
XL -Torso coil
32 Channel Torso/Cardiac coil
SENSE Torso/Endo coil^
SENSE Cardiac/Endo coil^
* Dual Coil possible at R2.5.3.
? Only Multi-coil allowed at R2.6.1
+ Dual Coil/SENSE compatible R18.104.22.168 and above
^ Dual Coil/SENSE compatible R2.6.1 and above
3.0T 6-channel Cardiac coil
32-channel Torso/Cardiac coil
While not required a good patient preparation will increase the quality of the outcomes obtained.
- NPO 4 hours prior to the examination - this reduces bowel motility.
- Empty bladder, have patient void prior to positioning for exam. This further reduces motion and significant displacement of the organ during data acquisition.
- Empty rectum/sigmoid - bowel cleansing treatment or enema just prior to the MR exam may be considered to eliminate trapped air pockets that will compromise susceptibility sensitive imaging techniques (DWI, spectroscopy).
- Administration of bowel motility inhibitors - further reduction of bowel motion.
As with all MRI, correct positioning of the patient and coils leads to better quality outcomes. It is well known that placing the anatomy of interest in the center of the surface coil, in the center of the magnet results in better SNR as well as decreased artifacts. The following workflow is presented to help obtain this:
- Placement of the array coil on the table (if using the Endo coil only, skip to step 4).
To ensure that the anatomy of interest can be moved completely into isocenter, the posterior half of the array coil should be placed on the table above the black dot. This black dot is the indicator of lowest point on table that can be moved to iso-center.
- Positioning the patient in relation to the array coil.
The patient should be placed onto the posterior half of the array coil in a head first position. It should be noted that the patient can be placed feet first if only the array coil will be used, if combination with the Endo coil is desired only the head first position can be used.
- Positioning the anatomy.
The prostate lies almost directly behind the symphysis pubis. This bony structure is easily located and by placing this landmark at the center of the coil one can be sure that the prostate is optimally positioned.
If using the array coil only skip to step 7.
- Positioning the Endo coil.
User should read and understand the user documentation for the Endo coil before proceeding. Due to the small size of the coil array accurate positioning of the coil is critical for optimal image quality. The blue mark on the handle of the disposable Endo coil is used to show the correct rotational position of the Endo coil conductors relative to the prostate. Position this mark facing anteriorly to ensure that the coil is facing the correct way.
- Secure the Endo coil.
Once positioned the user needs to inflate the balloon to remove the possibility of coil rotation. How this is accomplished is up to the user, however substances that produce high signal intensity should be avoided. Additionally, if the user is expecting to do spectroscopy or DWI, filling the balloon with air should be avoided as this will increase susceptibility artifacts. User should contact Medrad, (www.medrad.com), for recommendations concerning approved fluids that can be used to inflate the balloon instead of air. Upon inflation of the balloon the user must attach the plastic clip to the coil to further secure the coil removing the possibility of rectal migration.
- Finalize Endo coil set-up
After the coil is positioned plug it into the connector on the Endo cable assembly. The rectangular box of the cable assembly is positioned between the legs and the cable then routed under the leg of the patient. It is advised to wrap the cable assembly box with a small towel to improve patient comfort. Do not plug the cable assembly into the facade connector until the patient is positioned to magnet isocenter.
- Finalize array coil set-up
Place the anterior half of the array coil onto the patient, being sure to minimize the angulation of the elements as well as ensuring that the anterior and posterior elements are aligned.
- Final steps
Center on the array coil (or the symphysis pubis if using the Endo coil only) and insert the patient into the scanner. At this time plug the coil(s) into ODU connectors on the front of the magnet using the connector closer to the table for the endo coil. If only using the array coil either ODU can be used.
Improper Endo coil placement
Improper Endo coil placement
Proper Endo coil placement
Bright signal intensity indicates position of the coil element . Note that in this example the signal is appearing laterally.
Another example where the coil is not optimally placed. This time it is rotated to the patient's right side.
This example shows correct placement of the coil with the element facing anterior.
While every user has his/her own preferences when it comes to the ideal protocol for prostate imaging, there are some similarities found in every protocol. This section will discuss the acquisitions typically used.
Specific ExamCards from other Philips users can be downloaded below to provide a starting point for the development of your site specific imaging needs.
2D T2-weighted imaging provides the anatomical information about the prostate and the surrounding organs. This imaging is obtained to determine the internal structure of the organ not easily determined via digital exam or other imaging modalities. This imaging may also provide the interpreting physician with information to stage the extent of the disease.
Tip: To reduce the effect of respiratory motion artifacts on the final image it is recommended that axail and coronal imaging be obtained with a RL foldover direction. Obtaining sagittal imaging with F-H foldover direction will provide the same effect in this plane.
1.5T dual coil T2 axial
1.5T dual coil T2 coronal
1.5T dual coil T2 sagittal
2D SEEPI diffusion weighted imaging is used to aid in lesion detection. b-values above 1000 have shown significant sensitivity in defining areas of disease. These higher b-values cause the typical diffusion signal of the prostate to drop leaving only areas of restricted diffusion. These areas can then be correlated to the other imaging acquired for determination of their significance.
This dataset can be processed into ADC maps. Studies have indicated that lower ADC values may indicate abnormal prostate tissue. Image quality of the ADC map can be improved with the use of the advanced viewing Diffusion Registration tool (R2.6 or higher software).
3.0T dual coil multiple b-value DWI
T1 axial may be included in those patients that have recently undergone a biopsy to rule out hemorrhage.
3.0T dual coil T1 axial
3D T1 TFE is obtained to provide information about the uptake characteristics of the prostate. As with other organs abnormal areas demonstrate different enhancement patterns than that of normal tissue. Typically this data is acquired with a high temporal resolution (3 to 5 seconds). This requires the trade off in the resolution of the imaging to obtain the fastest possible acquisition.
3T dual coil DCE axial
3D CSI Proton Spectroscopy acquisition with surface coils is possible however the SNR at 1.5T is below the threshold to provide sufficient clinical benefit due to the larger voxel size required to get acceptable quality spectra. If spectroscopy is to be acquired at 1.5T the endo coil alone or dual coil imaging should be used for this type of acquisition.
Due to the unique nature of this imaging please refer to the NetForum document
10 Tips for Prostate Spectroscopy for further guidance: