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Fluke Nuclear Associates 76-907 Скачать руководство пользователя страница 25

Operation

Tests with Uniformity and Linearity (UAL) Phantom

2

 

 

 

 

 

2-15

Figure 2-12 is an image of the signal bubble for quadrature error. If there were any quadrature phase 
error, another ghost circle would be visible in the lower right-hand corner of the image. Quadrature error 
has become less common in most of the recent MRI systems. 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Figure 2-12 

 

Содержание Nuclear Associates 76-907

Страница 1: ...iates 76 907 and 76 908 AAPM MRI Phantoms Users Manual March 2005 Manual No 38616 Rev 3 2003 2005 Fluke Corporation All rights reserved Printed in U S A All product names are trademarks of their respective companies ...

Страница 2: ...Fluke Biomedical Radiation Management Services 6045 Cochran Road Cleveland Ohio 44139 440 498 2564 www flukebiomedical com rms ...

Страница 3: ...aration for Scanning 2 2 2 2 1 Positioning the Phantom 2 2 2 2 2 Scanning Parameters 2 2 2 3 Tests with 3D Resolution and Slice 3DRAS Phantom 2 2 2 3 1 Resonance Frequency 2 2 2 3 2 Signal To Noise Ratio 2 3 2 3 3 High Contrast Spatial Resolution 2 3 2 3 4 Slice Thickness 2 4 2 3 5 Slice Position and Separation 2 4 2 3 6 Example Images 2 5 2 4 Tests with Uniformity and Linearity UAL Phantom 2 10 2...

Страница 4: ... Blank page ...

Страница 5: ... magnetic resonance imaging systems These procedures and tests which are described in the AAPM document can be used to establish absolute performance standards as well as routine quality assurance programs The manual does not include procedures to measure any T1 T2 or proton density because at the present time there are no commonly accepted standard methods for determining T1 T2 and proton density...

Страница 6: ... mm and 2 0 mm side dimensions The spacing between the holes is equal to their side dimensions The holes are precisely parallel to each other and are long Square holes are used rather than drilled cylindrical holes because square holes can be manufactured more precisely than cylindrical holes Resolution Block Detail 2 Required Figure 1 2 Resolution Block Detail A set of two resolution sections are...

Страница 7: ...ckness Phantom Triangular blocks make 4 x 4 square with diagonal gaps of 1 or 2 mm Four triangular blocks are glued with 1 mm or 2 mm gap 1 4 2 mm Gap 1 mm Gap 2 mm Gap 1 mm Gap Filling Hole Resolution Block W Horizontal Holes Resolution Blocks w Holes into the Paper 2 Resolution Blocks w Vertical Holes Slice Thickness Block Groups 4 Box Dimension of the Box 6 x 6 Walls are Made with Material 3 ...

Страница 8: ...sections are included in the phantom in order to allow the slice thickness measurements in all three dimensions In a single multi slice scan the user can obtain images for signal to noise ratio resolution in two directions slice thickness and slice to slice gap 1 2 2 Uniformity and Linearity UAL Phantom 76 907 The UAL phantom has outer dimensions of 13 x 13 x 4 Figure 1 6 with a small bubble Figur...

Страница 9: ...e 1 6 UAL Phantom MRI Phantom for Spatial Linearity Signal To Noise and Image Artifact Figure 1 7 UAL Phantom with Side View 4 13 Glue Glue Glue Glue Flood Section Two Grids Stacked Glue Glue Glue 3 16 Wall Wall 1 Not to Scale 13 13 Glue Glue Glue Glue Linearity Grid Light Cover Glue Orientation References Not To Scale ...

Страница 10: ...of which can be used to measure the uniformity in signal intensity in the images The grid section consists of grids that can be used to assess geometric linearity A small pancake shaped container holding producing solution is attached on the diagonal surface of the phantom It is used to detect phase errors ...

Страница 11: ...ely linear with ion concentration Agent Concentration T1 T2 CuS04 1 2SmM 860 40 msec 625 38 msec NiC12 1 25mM 806 59 msec 763 66 msec Propanediol 0 100 2134 217 msec 485 72 msec MnC12 0 1 1mM 982 132 msec 2 1 2Filling the Phantom Degassed water should be used to make MR solution Water can be degassed by boiling and cooling The following amount of water should be prepared Cubical Phantom 4 000 cc 4...

Страница 12: ...sla system the resonance frequency should be 63 87 MHz Prior to the performance of any imaging protocol the resonance frequency must be checked first Changes in the resonance frequency reflect changes in the static magnetic field B field Changes in the B field may be due to superconductor run down typically on the order of 1 ppm day e g about 60 Hz day at 1 5 Tesla changes in current density due t...

Страница 13: ...sitioned in the center of the image and should not include any obvious artifacts The signal is the mean value of the pixel intensity in the ROI minus any offset An indication of the existence of an image intensity offset may be gained from an examination of intensity values from ROl s taken over non signal producing portions of a phantom Specific offset values should be obtained from the system ma...

Страница 14: ...one side and 2 mm gaps on the opposite side Slice thickness FWHM FWTM In the resultant image the signal level is read out across the ramp on a pixel by pixel basis along a line of interest oriented orthogonally to the ramp width dimension As noted previously to assure adequate S N it may be necessary to either use multiple excitations or several line profiles The FWHM or FWTM parameters should be ...

Страница 15: ... 22 msec and slice thickness of 3 mm This axial image from a body coil shows resolution holes of 2 mm 1 mm and 0 75 mm well resolved There are two sets of holes shown in vertical and horizontal directions The resolution image can be viewed in a zoom mode Thin vertical lines from the resolution pin within two black blocks are placed in other orientations and have no meaning in axial orientation Fig...

Страница 16: ...the phantom The resolution holes are well resolved in vertical and horizontal direction and the two slices are 6 mm apart SP 14 5 and 20 5 The slice thickness images of short vertical lines on top and bottom of the phantom image again are from the crossed hot ramps of 2 mm top and 1 mm bottom Figure 2 3 Figure 2 2 ...

Страница 17: ...olution and Slice 3DRAS Phantom 2 2 7 Figures 2 4 and 2 5 show two adjacent coronal views of the phantom The slice thickness lines of 1 mm ramps on the right and bottom of the images are too faint to be seen Figure 2 5 Figure 2 4 ...

Страница 18: ...e image against a background less opaque than in previous images indicating that the position of the resolution block is such that it is partially covered by the slice For resolution measure it is advised to use a slice that covers the central portion of the slice hole section Figure 2 6 ...

Страница 19: ...surement analysis A signal intensity profile is drawn vertically through a set of slice thickness ramp Images The profile is the slice thickness profile One can also obtain the slice thickness by measuring full width half maximum of the profile Figure 2 8 represents the same data using a larger zoom factor Figure 2 8 Figure 2 7 ...

Страница 20: ...min 2 S S max S min 2 The relationship for calculating integral uniformity U is U 1 R S x 100 Perfect integral uniformity using this relationship is when U 100 In some cases e g low field imaging signal to noise may be a limiting factor in the measurement of image uniformity To help minimize the effect of noise on the measurement the image may be convolved with a 9 point low pass filter For a 20 c...

Страница 21: ...g gradients for imaging and errors in both RF transmit and receive quadrature phase result in unique ghost artifacts A DC offset error is defined here as high intensity or low intensity pixels at the center of the image matrix due to improper scaling of low frequency components typically DC in the Fourier transformation of the NMR time domain signal 1 Phase encoding gradient instability 2 Quadratu...

Страница 22: ...the multi slice mode in which the phantom is placed at a location offset from the isocenter A transmit ghost appears in the slice located in the opposite offset direction at a distance equal to the distance at which the true object is located from the isocenter mirror image from the isocenter The ghost and true object image will be located at the same relative positions in their respective images ...

Страница 23: ...Operation Tests with Uniformity and Linearity UAL Phantom 2 2 13 Figure 2 9 ...

Страница 24: ... 10 is a flood image showing the uniformity of signal intensity Field non uniformity is also shown on the outer edges Figure 2 10 Figure 2 11 shows a horizontal intensity profile with a narrow window setting Such information can be used as baseline data Figure 2 11 ...

Страница 25: ...re 2 12 is an image of the signal bubble for quadrature error If there were any quadrature phase error another ghost circle would be visible in the lower right hand corner of the image Quadrature error has become less common in most of the recent MRI systems Figure 2 12 ...

Страница 26: ...Fluke Corporation Radiation Management Services 6045 Cochran Road Cleveland Ohio 44139 440 498 2564 www flukebiomedical com rms ...

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