Breast MRI Technology - Assignment Example

BREAST MRI TECHNOLOGY Student Name: Subject: Supervisor: Date of submission: 30th September, 2012 Assignment questions Q1. The common image artifacts associated with Breast MRI, and strategies used to minimize them Introduction An artefact is any artificial blemish or image that has undergone human manipulation or has been obtained due to lack of effectiveness or misinterpretation of the MRI sequence. There are several breast imaging modalities and just like them, the MRI of the breast has not been left out in giving artefacts resolutions pattany et al. (1987). Most often the breast artifacts are copycat pathology giving a vague outcome and thereof improper diagnosis. Unlike mammography, MRI is quite complex a fact which places these procedure to actually not easily recognize the artifacts and also making it harder in determining their specific cause. Several artefacts associated with the breast include:- Ghosting artifacts These structures are patients induced. These artefacts occur as a result of blood flow, motion of the cardiac or general tissue movement. Signals are obtained during this process offer data collection and which is also used for analysis. Motion causes the imaging to have bright ghostly structures and blurred image. This form of artefact is well reduced by breast immobilization and the repetition time. Breast immobilization results from respiration or shift of patient’s position during scanning. Figure below 1: indicating a motion artifact. Figure 1: Motion artifact imaging done using T2*W MRI. The imaging shows axial fat-saturated (http://radipgraphics.rsna.org/content/27/suppl_1/S131.full) Aliasing artifacts (wraparound or image wrap artifacts) During imaging each tissue has to be studied in a specific FOV (field-of-view) either in FE or PE direction. In some cases the signal-producing tissues may not only be directed to the tissue FOV but as well as the surrounding areas that were not made for study. The findings in this case give extra noisy to the structure resulting to pathology stimulation as well as obscure breast-details. Figure 2 below shows an example of wrap around artifact. To eliminate the impact of aliasing artifact, it is recommendable to oversample the number of FE steps factor two. This process has shown to suppress the tissue image wrap which do give signals on both sides of one FOV. Another procedure of ruling out this artifact is an application of NPW (no phase wrap). In this case, the PE steps are multiplied by a factor two which results to doubling time of imaging. Incase where the time of scan remains unchanged the artifacts are however, reduced. The acquisition of similar PE steps does not change the signal-to-noise ratio. Frequency oversampling and low-pass frequency filter combination is effective in lowering all forms of aliasing artifacts that are obtainable in the FE direction. This is because they do hold signals back that they do not produce an image beyond the chosen FOV Berg & Birdwell (2006). Figure 2: A T1*W MRI aliasing artifact (http://radipgraphics.rsna.org/content/27/suppl_1/S131.full) Truncation artifacts (ringing, Gibbs or edge artifacts) These artifacts result from restricted sampling that is obtained during MRI. They occur where there is a high contrast and sharp interfaces. All direction in-plane produce predetermined samples. There is high probability of artifacts developing outside the interface when correct signals are overextended or overshoot. Gibbs is the overshooting effect and it increases both the ringing and contrast interfaces of which they both cause light and dark banding. To reduce this form of artifact, selection of matrix or FOV that is able to produce submillimeter pixels in the two-directions is recommendable Hendrick (2007). Chemical shift artifacts The hydrogen in water normally has high frequency of resonance; however, the fat hydrogen nuclei may resonant at a different frequency. If this occurs then the chemical shift artifact is obtained. An example of this artifact is shown in figure 3 below. The results is white and black band which are usually perpendicular to the frequency encoding direction in cases where fat and water is found to be out of phase. Performance of fat-saturation is advocated to lower the signal from fat. Moreover, the effective form of reduction is achieved by keeping bandwidth per pixel high Johnson & Wisconsin University (2008). Figure 3: sagittal GRE MRI: chemical shift artifact (http://radipgraphics.rsna.org/content/27/suppl_1/S131.full) Metallic artifacts In other cases the magnetic field is disturbed by metallic pieces around the scanner causing metallic artifacts as in shown in figure 4. Such magnetic image field disturbance results from ferromagnetic metals which include cobalt, iron and nickel. These metals do have unique properties resulting from the unpaired electrons which in turn create a magnetic field. When the magnetism created is strong it destructs the MRI magnetic field. The results obtained following the acquisition of results with this form of ferrous metals magnetism disturbances produces warped images and void signals. Non-ferric materials also do produce artifacts although they are quite small as compared to those produced by ferrous metals. During any MRI pulse sequence is advisable to use Mammo-mark clips since they are known to produce quite minimal artifacts Chen, Lehman &Dee (2004). Figure 4: Axial fat-saturated artifact imaging of GRE T2*-weighted MRI (5210/123). The lumpectomy site shows surgical clips (http://radipgraphics.rsna.org/content/27/suppl_1/S131.full) Radiofrequency Transmission artifacts When MRI examination room is shielded it results in partial RF shielding which in turn creates these artifacts. A faraday cage comprising of a wire mesh which is placed in the inside walls, doors and windows of MRI room provide the RF shielding. When the RF shield breaks or the MRI room door is left open, distinct line images occur following radio transmission especially that are adjacent to Larmor frequency. The RF transmissions in turn are fixed in the direction of FE. However, in PE views these RF artifacts occur following different amplitudes and hence do smear in the PE direction. RF artifacts as shown in the figure 5 can as well be produced when the RF is fed through fixtures, light appliances or the transmit coils. This phenomenon produces broad lines. This lines cut-crossways towards the PE and along the image. It is advisable that regular review of the RF shielding should be done by service engineers. In addition, the lights in the scan room should remain on; a fact which is necessitated by peripheral electrical equipment usage. These two factors are known to rule out the occurrence of these artifacts Hendrick (2007). Figure 5: RF artifacts (http://radipgraphics.rsna.org/content/27/suppl_1/S131.full) Reconstruction artifacts Reconstruction artifacts form on the planar images inform of repeated lines and dots. These results from alteration that may take place before the image reconstruction of 2DFT or 3DFT or from data corruption measurement during signal acquisition. Malfunctions in MRI equipment may as well create these MRI artifacts. To limit the occurrence of this artifact, image data representations in the K-space need to be keenly looked into to either reveal or permit data correction following distortion. Qualified engineers need to take timely action in situations where the artifacts occur following apparatus breakdown. Q2. The clinical usefulness of spectroscopy in Breast MRI Introduction Spectroscopy is the study of wavelength in a given matter and the imposed radiations. In addition to breast magnetic resonance imaging of the breast examination, another recommended imaging is the magnetic resonance spectroscopy (MRS). The reason for this is because MRS has shown to be more particular in tumor differentiations between the malignant and the benign. While MRI sequences are good in ascertaining the presence of lesions the MRS imposes more advantages in defining the specificity of the lump. When histopathologic characterization is performed on breast tumors, of the total tumors signalized during mammography three quarters and a half of those identified using contrast-enhanced MRI have been found to be cancers JNCI (2002). The breast chemical content information is collected using in vivo MRS method alongside MRI. This information collected relies on a method known as single voxel. The information obtained is of principal importance in a number of clinical applications. These applications do include the response monitory to cancer therapies as well as accuracy improvement on lesions diagnosis. Currently, the MRS research is being included in line with MRI procedures and hence most initial studies do give positive results in regard to the breast cancer. Therefore, MRS is the most recent used method in breast lesions monitory, treatment and diagnoses solving technique Bolan et al (2005). Bolan et al, (2005) points out that the differentiation of benign from malignant lesions using MRS is the first application most researched on in regard to breast even before a biopsy is performed. Among the early researches in this field is the use of total choline (tCho) which was recommended to mark malignancy. Although more studies which followed applied other fairly methods than this, they also applied this theory. Regardless of subsequent studies the studies obtained gave consistent outcomes. A study carried by Katz-Brull and colleagues indicates that these methods gave encouraging results of 83% sensitivity and 85% specificity. In addition, the malignancy determination was quite independent in that, it did not involve any clinical diagnostic or historical information consideration a fact which was also very encouraging. The use of MRS of the breast in cancer treatment is the second application. In this case, it is applied to predict the reaction of the cancer cells to treatment. current palpations and imaging methods which are in use do rely on the tumor size changes which may take weeks to several weeks in order to identify such swelling as cancer tumors or not. The breast MRS on the contrary has the capacity of identifying and distinguishing intracellular metabolism early enough before any morphological changes which may be unpleasant crops in Nass et al., (2001). Q3. The Magnetic Resonance Elastography (MRE) and its advantage to breast MRI examination MRE is a form of body imaging technique. It applies both the sound waves and MRI of which both are known to give an elastogram (visual image). The result obtained gives information of the body tissues in regards to their elasticity or stiffness. MRE is quite new in the imaging field and is applied in liver study to identify change in liver morphology following diseases impact. Moreover, MRE can as well be used noninvasively to study and diagnose diseases in other human body parts. Elasticity does have many purposes in the clinical application. Some of these essential uses of elasticity are in palpation or percussion processes done during physical examinations of different body parts or organs in clinical set up. Every organ has its unique elasticity degree and, therefore, the difference in changes of this elasticity is used in identifying tumor presence and spread. In liver diagnosis, elasticity plays a major role in liver cirrhosis and tissue necrosis degeneration study Ehman (2011). Different material do have different index of stiffness and just a mere sense of touch can tell the softness and hardness of a substance. Differentiating hard materials such as metals from rubbers is possible following this fact. The same is possible when a touch is applied on human body to study tissues of the internal organs. To this regard, noninvasively index measure of tissue stiffness is possible, therefore, necessitating diagnoses. This characteristic is used in various disease diagnoses as well as liver cirrhosis and necrosis (for both hard and soft tissue). In addition, tissue elasticity is required by other systems which do arouse deformation of tissues in patient. Such systems are the computer assisted surgery and telepalpation which use finite element method or the mass spring model. MRE has shown its advantage in the MRI examination of the breast over physical manual examination of body organs by hand as it is done by the physician in that it is able to palpate body organs noninvasive where the human hand can not reach. In addition, it can define tumors in the body early enough before they grow and become serious such that they can be identified by human hands. Another advantage of MRE is its superiority to sense changes that occur in tissue-mechanical-properties. Moreover, it is excellent in tissue outlining a fact which is made possible by the ability of MRE to provide biomarkers imaging technique quantitatively Donald & Plewes et al. (2000). The use of elastography allows ultrasound or MRI to measure breast tissues-mechanical-properties from one point to the other inside the breast. The mapping of the measurement is then done on the elastograms. In conclusion, Elastogram is an image either a two-or three- dimensional. References Berg W. & Birdwell R., (2006). Diagnostic imaging: Breast. Salt lake city: Amirsys, inc Bolan P. J. et al., (2005). ‘‘Imaging in breast cancer: Magnetic resonance spectroscopy’’. Breast Cancer Research, Vol. 7 (4) 149-152 Chen X., Lehman C.D. & Dee K.E., (2004). ‘‘MRI-guided breast biopsy: clinical experience with 14-gauge stainless steel core biopsy needle’’. AJR; Vol. 182: 1075-1080 Donald & Plewes D.B. et al (2000). “visualization and quantification of breast cancer biomechanical properties with magnetic resonance elastrography”. Physics in medicine and biology. Vol.45 (6) Ehman R.L., (2011). Magnetic Resonance Elastrography. Retrieved September, 2011 from http://mayoresearch.mayo.edu/ehmanlab/mre.cfm Hendrick R.E., (2007). Breast MRI: fundamentals and technical aspects. New York: springer JNCI, (2002).”clinical utility of proton magnetic resonance spectroscopy in characterizing breast lesions”. JNCI journal of national cancer institute. Vol. 94(16): 1197-1203) Johnson K.M. & The University Of Wisconsin-Madison., (2008). Acceleration and correction of phase contrast velocimetry for angiography and hemodynamic quantification. Michigan: ProQuest Nass S.J. et al., (2001). Mammography and beyond: developing technologies for the early detection of breast cancer. Washighton: National Academic Press Pattany P.M. et al., (1987). “motion artifact suppression technique (MAST) for MR imaging”. Journal comput. Assist. Tomogr. Vol. 11:369-377 Read More

This process has shown to suppress the tissue image wrap which do give signals on both sides of one FOV. Another procedure of ruling out this artifact is an application of NPW (no phase wrap). In this case, the PE steps are multiplied by a factor two which results to doubling time of imaging. Incase where the time of scan remains unchanged the artifacts are however, reduced. The acquisition of similar PE steps does not change the signal-to-noise ratio. Frequency oversampling and low-pass frequency filter combination is effective in lowering all forms of aliasing artifacts that are obtainable in the FE direction.

This is because they do hold signals back that they do not produce an image beyond the chosen FOV Berg & Birdwell (2006). Figure 2: A T1*W MRI aliasing artifact (http://radipgraphics.rsna.org/content/27/suppl_1/S131.full) Truncation artifacts (ringing, Gibbs or edge artifacts) These artifacts result from restricted sampling that is obtained during MRI. They occur where there is a high contrast and sharp interfaces. All direction in-plane produce predetermined samples. There is high probability of artifacts developing outside the interface when correct signals are overextended or overshoot.

Gibbs is the overshooting effect and it increases both the ringing and contrast interfaces of which they both cause light and dark banding. To reduce this form of artifact, selection of matrix or FOV that is able to produce submillimeter pixels in the two-directions is recommendable Hendrick (2007). Chemical shift artifacts The hydrogen in water normally has high frequency of resonance; however, the fat hydrogen nuclei may resonant at a different frequency. If this occurs then the chemical shift artifact is obtained.

An example of this artifact is shown in figure 3 below. The results is white and black band which are usually perpendicular to the frequency encoding direction in cases where fat and water is found to be out of phase. Performance of fat-saturation is advocated to lower the signal from fat. Moreover, the effective form of reduction is achieved by keeping bandwidth per pixel high Johnson & Wisconsin University (2008). Figure 3: sagittal GRE MRI: chemical shift artifact (http://radipgraphics.rsna.org/content/27/suppl_1/S131.full) Metallic artifacts In other cases the magnetic field is disturbed by metallic pieces around the scanner causing metallic artifacts as in shown in figure 4.

Such magnetic image field disturbance results from ferromagnetic metals which include cobalt, iron and nickel. These metals do have unique properties resulting from the unpaired electrons which in turn create a magnetic field. When the magnetism created is strong it destructs the MRI magnetic field. The results obtained following the acquisition of results with this form of ferrous metals magnetism disturbances produces warped images and void signals. Non-ferric materials also do produce artifacts although they are quite small as compared to those produced by ferrous metals.

During any MRI pulse sequence is advisable to use Mammo-mark clips since they are known to produce quite minimal artifacts Chen, Lehman &Dee (2004). Figure 4: Axial fat-saturated artifact imaging of GRE T2*-weighted MRI (5210/123). The lumpectomy site shows surgical clips (http://radipgraphics.rsna.org/content/27/suppl_1/S131.full) Radiofrequency Transmission artifacts When MRI examination room is shielded it results in partial RF shielding which in turn creates these artifacts. A faraday cage comprising of a wire mesh which is placed in the inside walls, doors and windows of MRI room provide the RF shielding.

When the RF shield breaks or the MRI room door is left open, distinct line images occur following radio transmission especially that are adjacent to Larmor frequency. The RF transmissions in turn are fixed in the direction of FE. However, in PE views these RF artifacts occur following different amplitudes and hence do smear in the PE direction. RF artifacts as shown in the figure 5 can as well be produced when the RF is fed through fixtures, light appliances or the transmit coils.

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