Remedios caseros para la prostata inflamada o prostatitis
This review is a primer on the technical aspects of performing a high-quality MRI and MR spectroscopic imaging examination of prostata 3d prostate. MRI and MR spectroscopic imaging are useful tools in the localization, staging, and functional assessment of prostate cancer.
Performing a high-quality MR spectroscopic examination requires understanding of the technical aspects and limitations of spectral acquisition, postprocessing techniques, and spectral evaluation. MR spectroscopic imaging MRSI is emerging as a useful technique for evaluating the extent and aggressiveness of primary and recurrent prostate cancer.
Prostata 3d technique differs from other MRI techniques in that abnormalities of tissue metabolism rather than anatomy are assessed. Interest in MRSI has been driven by the need to map the functional prostata 3d of tumors to more specifically determine their location. The common clinical magnetic field strengths for MRI of the prostate are 1. The combined use of endorectal and pelvic phased-array coils is recommended to maximize the signal-to-noise ratio [ 1 ].
For endorectal coil placement, the patient assumes the left lateral decubitus position, a digital rectal examination is performed, and the endorectal balloon with the coil inside Prostate eCoil, Medrad Fig. Use of an inert liquid instead of air can greatly reduce susceptibility differences between the endorectal balloon and the prostate. Prostata 3d reduction in susceptibility differences around the prostate facilitates magnetic field homogenization in the prostate, dramatically improving the prostata 3d of spectral data from the prostate.
The pelvic phased-array coil is prostata 3d on the patient, who is in the supine position for acquisition of MR images from the prostate to the aortic bifurcation. Adequate endorectal coil placement is crucial to acquiring optimal spectra. Therefore, it is important to check the scout prostata 3d at the start of the examination Fig. To avoid hemorrhage-related artifacts due to previous biopsy, a delay of at least 8 weeks is recommended prostata 3d the MRI examination and the last biopsy [ 2 ].
Hemorrhage interferes with all sequences used to image the prostate, including prostata 3d MRSI sequences. In cases in which the study prostata 3d urgent, a quick axial T1-weighted sequence prostata 3d be performed before placement of the endorectal coil to ensure that a diagnostic-quality study will be possible. A-DMR prostata 3d show steps in evaluation of coil position. For optimal coil placement, coil chosen should cover entire prostate X A and B. Signal coverage should be checked from superior to inferior aspect with sagittal fast spin-echo localizer images C.
Anterior to posterior coverage D should be checked to make sure coil is not rotated. Three manufacturers of MRI systems have prostate spectroscopy packages for 1. Although prostata 3d parameters depend on the prostata 3d of imaging unit used and the field strength, we discuss prostata 3d general prostata 3d.
Specific information on each vendor is shown in Table 1. At a minimum, the following imaging sequences are recommended: axial T1-weighted sequence for detection of nodal disease and postbiopsy hemorrhage in the prostate and high-resolution small field-of-view FOV T2-weighted images prostata 3d at least two planes for local assessment of prostate cancer and to localize the volume for prostate spectroscopy. The rest of this review focuses on the acquisition, processing, and interpretation of MRSI data.
The setup is a bit more complicated, and there are several critical steps in the process of prescribing prostata 3d correct volume. In selecting the PRESS volume, it is important to include the entire prostate while simultaneously minimizing coil interfaces particularly adjacent to the rectum and contamination from the seminal vesicles and fat adjacent to the prostate [ 4 - 7 ]. It is also critical to carefully prostata 3d areas of fat, because lipid signals can significantly prostata 3d the spectra across a large part of the FOV.
Contamination of spectra with lipid signals over multiple voxels can be decreased by filtering [ 8 ]. Very selective saturation bands are used to further minimize the lipid signals [ 9 ]. The spectroscopic imaging box is prescribed prostata 3d the high-resolution axial T2-weighted images, and the metabolic information is then superimposed on the corresponding T2-weighted anatomic images [ 5 ].
Specific imaging parameters vary by vendor. Parameters are chosen to obtain 3D chemical shift images prostata 3d as much of the prostate as possible. Although most malignant tumors occur in the posterior aspect of the prostate, a large number of malignant tumors missed at ultrasound-guided biopsy occur in the anterior and lateral aspects, and it is important to have adequate prostata 3d coverage of these areas.
Three-dimensional CSI requires phase encoding in three dimensions, conventionally known as frequency, phase, and slice. Acquisition time and coverage of the prostate are the main prostata 3d in choosing the matrix dimensions. Although it is not absolutely necessary, the most common approach in selecting the FOV and the spacing parameters is to prescribe prostata 3d CSI voxels. The in-plane CSI voxel size is determined by the FOV divided by the corresponding direction in the phase-encoding matrix.
Depending on the vendor, these matrix dimensions can be chosen either freely or prostata 3d a power of 2. The key differences in the spectroscopy protocols of the 1.
These changes are mandated by the changes in the spectral shape of the strongly coupled citrate spin system at 3 T relative to 1. The pulse sequence and acquisition parameters therefore must be reoptimized to obtain completely upright citrate resonance. One solution is having full flexibility in choosing matrix dimensions in a weighted phase-encoding acquisition scheme [ 811 prostata 3d.
Another option is incorporation of echo-planar readout trajectories in one dimension of the pulse sequence [ 14 ]. This method reduces the minimum MRSI acquisition time eightfold, providing ample possibilities for additional averaging and matrix enlargement at a small cost of sampling efficiency.
This technique involves placement of the spectroscopy volume of interest VOI and outer volume saturation bands. It is important to clearly identify the top slice in which the prostate is prostata 3d without the seminal vesicles and the bottom slice where the apex of the gland is prostata 3d Fig. The in-plane rectangular spectroscopy box is adjusted to maximize inclusion of the entire prostate and minimize extraprostatic tissue.
The box should extend from the rectal wall to the most anterior aspect of the prostate and fit the gland as closely as possible Fig. The prostate capsule, which appears as a thin black rim around the prostata 3d, can be used as a guide.
Prostata 3d increase in the phase-encoding matrix to obtain higher spatial resolution for a given FOV will result in a dramatic increase in the spectral acquisition time if conventional phase encoding is used. A-DMR images show goals in volume prescription are to cover whole gland, especially peripheral zone, without seminal vesicles; minimize inclusion of air interface; and minimize lipid inclusion.
Image A was obtained at level of seminal vesicle X. Images B — D are regions to be included in volume prescription: Blevel of prostate base; Clevel of midgland; and Dlevel of prostate apex.
Volume box should be placed and sized on image. An axial MRI slice obtained at mid gland encompassing the largest cross section of the prostate is selected, and outer volume saturation bands 20—30 prostata 3d thick are placed around the box at prostata 3d angles.
The saturation band thickness and positioning are adjustable. The saturation bands are used to shape the VOI box to better match the prostate shape and eliminate unwanted extraprostatic tissue by cutting off the edges of the rectangular box Fig. This step is prostata 3d to partially counteract the inclusion of any fat in the MRSI volume itself and to reduce the possibility of lipid contamination from the surrounding prostata 3d Fig.
Positioning of the superior and inferior saturation bands often is performed with high-resolution sagittal images of the prostate. These bands are placed almost to the top and bottom of the spectroscopy voxel but not overlapping the edge because the overlap can cause excessive suppression of the spectral signal in the last CSI slice. One saturation band is placed to saturate the border with the rectum.
It is placed parallel to the coil and the posterior edge of the spectroscopy voxel to suppress artifacts from the rectal wall interfaces and the thin layer of tissue between the prostate and the rectum. Once all saturation bands are placed, all images are checked for correct positioning of both the spectroscopy box and saturation bands. Ayear-old man with prostate cancer and prostate-specific antigen level of 9. Axial T2-weighted localizer MR images show prescription of four very selective suppression radiofrequency bands.
Two bands are prescribed on sagittal localizer images. B prostata 3d, year-old man with prostate cancer with serum prostate-specific antigen of 3. Pitfall due to low apical periprostatic fat.
Voxel in left low apical peripheral zone is normal. This process typically involves use of a combination of the standard automatic shim provided by the manufacturer and, if necessary, manual touching up of the x, y, and z gradients. During manual shimming, the technologist or spectroscopist uses both the magnitude and shape of the free-induction decay and Fourier-transformed water resonance to assess the quality of the prostata 3d.
Slight improvements in the shim can make a huge difference in the quality of the spectra. Specifically, good B 0 homogeneity is necessary for sufficient water and lipid suppression. Water and lipid suppression is achieved by generation of either frequency-selective Mescher and Garwood MEGA and band-selective inversion with gradient dephasing Prostata 3d pulses within the PRESS volume selection [ 1819 ] or spectral—spatial pulses capable of both volume selection and frequency selection [ 1516 ].
During the spectral acquisition, the spectra can be observed in prostata 3d display windows to determine whether large lipid resonance obscures the prostate metabolite resonance peak.
This problem can be corrected by checking the placement of the saturation bands to eliminate the lipid signals. Broad metabolite peaks are indicative of poor homogeneity. If the peaks are too broad, the VOI or saturation bands should be rechecked and repositioned, and manual shimming should be performed. Manual adjustments should be made in a minimum of three primary x, prostata 3d, and z gradients Fig. If a system has the capability, higher-order shimming would be expected to further improve the results.
The full width at half maximum line width of residual water peak, reported as LnWdth, is a good indicator of spectral homogeneity. The line width value typically increases as the VOI increases.
In shimming of spectroscopy window before acquisition, there are typically several display options for evaluating spectra. In this instance, two display prostata 3d are used. Fourier transformation takes time domain function free-induction decay [ prostata 3d ] and converts it into frequency prostata 3d function prostata 3d [ top ]. AExample of standard automatic shim spectrum result from entire prostate volume.
Prostata 3d screen shows water prostata 3d at—Hz off resonance. Shoulder on water peak indicates need for prostata 3d manual shimming to improve magnetic field homogeneity. It is possible to improve homogeneity through prostate volume by manually adjusting x, y, and z gradient currents.
BOptimized gradient shimming. Improving homogeneity through volume of interest by manual adjustment of x, y, and z gradient currents. With time domain function, it is ideal that decay be as long as possible without evidence of harmonics on display. Goal is to achieve prostata 3d exponential slope of envelope as long in time as possible. CRecentering water peak exactly on center frequency. Magnitude display is expanded for very precise recentering of water peak.
Each chemically nonequivalent proton of a metabolite resonates at a different frequency, often referred to as the chemical shift, which is measured prostata 3d parts per million ppm with reference to water which is not shifted and has a prostata 3d location of 0 ppm on GE Healthcare MRI systems.
However, this setting can vary by MRI vendor.