Common Image Artifacts Associated With Breast MRI - Essay Example

Breast MRI Presented by Name Presented To Lecturer Institution Topic Date Q1. Common Image Artifacts Associated With Breast MRI and the Strategies used to Minimize them: Over the past years, breast cancer has been the killer in the United States. Breast MRI is increasingly becoming an adjunctive diagnostic imaging technique for diagnosing breast cancer. In fact, investigations reveal its ability to provide crucial and necessary information that neither physical examination nor mammography tests can provide (Orel and Schnall 2001) Undesirable artifacts may lead to breast magnetic resonance imaging (MRI), resulting from the patient and the technical factors. Practical application of a devoted isobilateral breast gyration, an MR imaging system which is of high field, and an optimum imaging means, gives a solid model for executing high quality breast MRI. There are major problems related to positioning of breast, phase-encoding direction, and imaging selection volume, which have a solution by training and providing feedback to MRI engineers. The most artifacts issues observed during the MR imaging include motion, suboptimal fat, metallic, suppression, susceptibility, radiofrequency, phase wrap, chemical shift and noise. Many of these artifacts at the time of recognition, the right correction measures may be undertaken. Feedback from radiologists on imaging and protocol supervising are critical in facilitating advanced breast MR imaging (Athanasiou, 2007). Over the past decade, there has been increase in the number of usages of breast magnetic resonance (MR) imaging. The latest potential indications for contrast material used in enhancing breast MR imaging include contra-lateral detection of breast cancer in newly diagnosed cases. Also, evaluation of breast cancer patients who require breast conservation is done. Thirdly, it involves screening of women who are at high risk for developing breast cancer. It also involves assessment of response to neo-adjuvant therapy for women. Evaluation of chest wall invasion in patients with posterior carcinomas is another indication that is in the MR imaging. Lastly, it involves detection of breast cancer in women with alar metastasis and normal mammographic findings. Breast MR imaging requires high spatial resolution, excellent fat saturation, and rapid carrying out of post-contrast sequences thus making the MR imaging a technological issue. Because of these patient and technical issues, breast MR imaging artifacts can in turn occur. Therefore, the artifacts may degrade the quality of the image thus confusing interpretation of the images. Studies on the Breast MR imaging may be on the one type of MR imaging fields that some radiologists interpret. Particularly, those who are committed solely to the analysis of the breast imaging may relate their studies to the technical factors that contribute to optimal studies, which are hard to recognize since they have less or minimal experience with MR imaging in general. In this report, there is review on the basic breast MR imaging techniques and major discussions made to illustrate patient and the related technical factors that may result in artifacts. In addition, there are major suggestions that are practical on how to improve the quality of solving the breast MR imaging issue. Ghost artifacts, susceptibility artifacts, aliasing artifacts and chemical shift artifacts are some of the artifacts. These are the only artifacts that are in this review but there are other artifacts about breast MR imaging. Motion artifacts During the breast MRI process, there are two types of motions that can result into image artifacts; physiologic motion and non physiologic motion. In addition, there are two basic categories of motion associated with Breast MRI. These include periodic and random motion. Any kind of movement occurring in the field of view during the imaging process has the consequence of degrading the image. Ghosting (ghost artifact) is caused by periodic motion and this result into obscuring the image with the consequence of fooling the reader of the image. On the other hand, random artifacts make the images to become blurred. In general, physiologic motion arises as a result of movement of fluids inside the breast tissue such as blood in the blood vessels, bowel fluids as well as pleural fluid and this motion results into ghosting (or ghost artifacts). Ghost artifacts Ghost artifact occurs as a result of different resonant frequencies of fat and water that are excited within the same slice (Tanenbaum, 2006). They are acquired images that almost look like they are patient induced. As it is, the images are misregistered by the Fourier, transforms and appears as a bright or dark band in the frequency direction for all the MR imaging tested. Ghost artifacts have a structure that looks like noise patterns that is in a phase encoding. According to Golsch (2010), chemical shift decreases by increasing the bandwidth. Spectroscopy actually benefits in increase in chemical shift due to it producing greater SNR and spatial resolution of individual metabolites. The metabolite peaks have greater separation at 3T compared to 1.5T, which results in greater accuracy in metabolite identification (Dietrich et al., 2008). Nevertheless, the 1.5T breast MR imaging system is best for breast imaging. Figure 1 below demonstrates the breast MR image in the Ghost artifact. Figure 1: A shows the motion effect that has resulted due to ghost artifact, while B is the ghost artifact image. Non physiologic motion Non physiologic motion arises mainly due to anxiety of the patient and/or claustrophobia and the image artifact related to this type of motion results into unsatisfactory MR images being produced. Since image artifact arising from this type of motion depends on the physiological and psychological state of the patient, strategies to minimize this artifact are mainly based on making the patient comfortable during the breast MRI procedure and/or restraining the patient to minimize or prevent motion. Therefore, the following strategy helps in minimizing the image artifact associated with physiologic motion. Ensuring that the patient is comfortable during the imaging process such as: Restraining the patients by the use of straps, Giving the patient some sedatives, Communicating with patient frequently by letting him be aware of the study Providing a fan in the examination room, among others. Considering motion artifacts in general, there are various strategies that one can use in reducing motion artifacts in breast MR images. The obvious one seems to minimize or completely eliminate the motion causing the image artifacts. Sometimes the artifacts are caused by structures that have no interest in the imaging process such as subcutaneous fat layer. A simple strategy to minimize this is to use a saturation band that is placed over the structure in motion (such as the subcutaneous fat for instance). Aliasing artifact Signal increase in the Breast MRI beyond the normal time limit causes a homogeneity increase leading to dielectric effects that are usually caused by eddy currents from the body tissue conductivity. This causes an increase in indifference on how the 2D and 3D imaging appears in relation to PE direction. RF wavelengths are usually shorter at 3T than at 1.5T. This causes the phenomenon to take place at field strengths that are high. This effect is particularly prominent when imaging larger anatomical areas such as livers on thinner patients. The area of homogeneity results in a drop off signal in a particular area. To decrease dielectric effect, a dielectric pad replaceable between the anterior body array and the patient, requires the use of coil (Duggan-Jahns, 2008). Strategies used to minimize aliasing artifacts include: Taking a larger field during imaging in breast MRI Oversampling: this means taking more sample images so that those with image artifacts can be ruled out. However, this strategy has disadvantage in that it increases the imaging time. Figure 2: an illustration of MRI for PE direction on the breast Susceptibility Artifact This artifact usually describes the degree of magnetization of a material placed in a magnetic field (Degani et al., 1986). It varies depending on the type of material. However, this susceptibility can affect the overall homogeneity of the magnet. Shimming is the best way to compensate for some of the homogeneities created by the interacting magnetism, and some by changing sequences and parameters, but some inevitably create an artifact appearing as a signal void. The susceptibility variations effects are usually proportional to the magnetic field strength. That is, a 3Tesla magnetic would have twice the large frequency variations than a 1.5Tesla and hence have a more prominent susceptibility artifact. Materials such as metallic implants and surgical clips cause susceptibility artifact and the sequence most affected by the susceptibility artifact is the gradient echo. To reduce the artifact, the TE (time echo) decreases and the receiver bandwidth increases (Dietrich et al., 2008). Figure 3: shows susceptibility artifact due to an embolization coil Q2. Clinical usefulness of spectroscopy in Breast MRI Basically, spectroscopy concerns the interaction between radiated energy and matter. The role played by this MR imaging on the breast monitoring is majorly to help the women with breast problem to have better diagnosis means. Of late, breast cancer has been a disease of high prevalence and incidence in women, especially those in industrialized countries. For instance, Greenlee et al. (2000) indicates its incidence as about 180, 000 every year in the United States. This indicates that health providers must use effective diagnostic tools in order to ensure successful treatment of the disorder. Various screening methods are in use in the attempt to detect breast cancer, including ultrasonography, palpation and mammography. According to Orel and Schnall (2001), use of magnetic resonance imaging (MRI), as a secondary diagnosing tool, has been on increase. All these methods help in the detection of a lesion, an indication of the possibility of breast cancer. Detection of the lesion does not indicate the end of the screening since it is very crucial to know whether the lesion is benign or malignant. The use of MRS (magnetic resonance spectroscopy) along with breast MRI assists in detecting tissue metabolism. Women with breast cancer have been observed to have some distinct changes in their metabolite content, a situation not found in benign breast lesions. Such alterations, found in breast cancer include increased phosphomonoesters and phosphodiesters content as well as increased composite choline content (Ronen and Leach 2001). Phosphomonoesters and phosphodiesters are usually detected by use of P MRS while composite choline is detected by H MRS (Jogannathan et al.2001). In general, according to Jogannathan et al. (2001), a normal breast tissue and a benign tumor have a similar biochemical profile and both have low contents of phosphodiesters and phosphomonoesters as well as composite choline. On this note, using spectroscopy, especially H MRS of the breast, in conjunction with breast MRI examination helps in improving the specificity of establishing and distinguishing malignant breast tumors and benign breast tumors. Kwock et al. (2006) indicate that magnetic resonance spectroscopic imaging (MRSI), when used in conjunction with MRI helps in providing more information about a tumor regarding its location as well as its infiltration extent. This information is helpful in making clinical management decisions regarding the best treatment for the tumor. For instance, this information is necessary in deciding whether there should be immediate intervention to the cancer or a watchful waiting is necessary. The number of challenges in the acquisition of the diagnostic methods of the cancerous developments in the breast and the rate of development has been determined using the MRS studies and the systems that are necessary for the automation of the systems used (Frey et al., 2006). From the in vivo research, the results show use of the MRI and breast MRS in detecting the distinguishing factors on the breast cancer development. The positive values that in the recent past are because of the breast sensitivity determining the malignant tumors that are detectable by the MRI and the MRS (Ophir et al., 1997). Conclusively, spectroscopy, when used in conjunction with breast MRI is useful in providing additional and necessary information regarding the status of the cancer. This information is essential in making decisions regarding the clinical management of the disorder and thus for the successful treatment of breast cancer. Q3. Magnetic Resonance Elastography (MRE) Magnetic Resonance Elastography (MRE) is a medical imaging technique used in propagation of the mechanical waves by the use of MRI. Biological tissues exhibit some elasticity and this means that it is possible to use the elastic properties of a tissue, say breast tissue, to determine whether there are problems with the tissue. For instance, there is a great difference between the elasticity of tumors and edemas and that of a healthy tissue. This means that a healthy breast tissue has different elasticity compared to a tumor. This is the basis of operation of MRE (Magnetic Resonance Elastography) which is a technique used to measure the mechanical properties of a tissue (biological) (Paulsen, Meaney and Gilman 2005). The technique non-invasively develops images for the elasticity of a tissue such as a breast tissue. To distinguish between the normal and abnormal tissues, there is a need to use the MRE. Transllumination of the breast is in theory of the normal and the abnormal tissue utilities as it is related to the transllumination. The use of Imaging diagnostics systems is as per the hybrid imaging techniques that are used to combine the acoustic imaging used to map the optical absorption of the biological tissue signal (Dietrich et al., 2008). The conventional mammography is the alternative proven breast transllumination for solving the issue that has been disturbing the research on the examination of the breast MRI. There is less or not enough research results that can be used in the development of the diagnostic evaluation of the breast MRI and MRE. In the 2006 meeting, the gynecology devices used to evaluate the risk of the breast used the MRE and the MR imaging (McRobbie et al., 2003). The ages that had undergone the diagnostic programme included the ages of 30 to 40 years in the arm of study about the usual population of the breast issues. Breast MRE risk assessment reports indicate reasonable indicator of the future risk on the breast by cancer cases and the related problems (Golsch, 2010). The main measure for the tissue’s elastic properties is elastography. Breast MRE is useful when detecting the cancerous lesions deeper in the breast and this gives an important value of the breast MRE. This technique involves the manual palpation of the breast cancer detection using the magnetic resonance and therefore relating to the importance of the MRE and MR imaging since it becomes cost effective for the application of the technology. For the success of the MRE and MR imaging, there has been the use of 3 major elasticity imaging types. First, the elastography that can track the movement of the tissues in the process of estimation of the strain is used. Secondly, elasticity imaging that involves shear wave propagation tracking through tissue to obtain the modulus of elasticity is applied (Katz-Brull, Margalit, & Degani, 2001). Lastly, there is elasticity imaging that uses sonoelastography by application of the Doppler Effect to enable generation of the movement of the tissues response in relation to the external vibrations. Using the three elasticity-imaging effects, there is assurance that the additional value of the magnetic resonance elastography follows the required constant MR imaging. Studies indicate that malignant tumors can have a stiffness value that is 13 times higher than that of normal or healthy breast tissue as well as benign tissues. This indicates that a breast MRE test is essential when conducted alongside breast MRI since while a breast MRI detects the presence of tumors or lesions in the breast tissue, a breast MRE test will in addition to this indicate or differentiate whether the tumor is a malignant one or a benign one, taking into considerations the difference in elasticity between the two types of tumors. The malignant and benign tumors differentiation is helpful in increasing the specificity of a breast MRI as a breast cancer screening method. References Athanasiou, A., 2007. Optical Mammography: A New Technique for Visualizing Breast Lesions In Women Presenting Non Palpable BIRADS 4-5 Imaging Findings: Preliminary Results With Radiologic-Pathologic Correlation. Berlin: Springer. Degani, H., Horowitz, A. & Itzchak, Y., 1986. Breast tumors: Evaluation with P-31 MR spectroscopy. New York: Wiley. Dietrich, O. et al., 2008. Artifacts in 3-Tesla MRI: Physical Background and Reduction Strategies. Radiolo, 65 (1), pp. 29-35. Duggan-Jahns, R.T., 2008. The Evolution of Magnetic Resonance Imaging: 3T MRI in Clinical Applications. New York: Cambridge University Press. Frey, H. et al., 2006. Real-Time Elastography--An Advanced Method Of Ultrasound: First Results In 108 Patients With Breast Lesions. Ultrasound Obstet Gynecol, 228 (3). Golsch, A., 2010. 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