Breast Magnetic Resonance - Essay Example

? Breast MRI Breast magnetic resonance is a powerful tool that has gained immense prominence in breast cancer, research and treatment over the past decades (Hendrick 2007, p. 30). Potential applications of breast MRI include the examination of the extent of damage of breast cancer in affected women, examination of contralateral breast cancer in the newly diagnosed breast cancer patients, screening of breast cancer in women at high risk of developing the condition, and assessment of the efficacy of various cancer treatments. It is also used in examining the extent of chest wall invasion in breast cancer patients with posterior carcinomas, and the diagnosis of breast cancer in women portraying normal mammographic examinations and presence of axillary metastasis (Torosian 2002, p. 211). The process of conducting breast MRI is a highly demanding procedure that requires consideration of several factors in order to come up with useful breast images (Liberman 2005, p. 78). Essential factors to include are excellent fat saturation, high spatial resolution and rapid performance of post contrast sequences. Failure to take into consideration these factors can cause breast MRI artifacts. The artifacts are responsible for the generation of poor quality images that may cause a misdiagnosis of the condition. In some breast cancer research centers, MRI acts as the sole imaging tool. Therefore, lack of experience in identification of the different artifacts may produce suboptimal studies that are not helpful in diagnosing breast cancer (David 2006, p. 166). In most cases, the presence of artifacts obscures pathology, which makes it difficult to obtain a correct diagnosis. However, the ability to detect the presence of artifacts reduces or eliminates artifacts in future diagnostic procedures (Hendrick 2007, p. 187). Examples of potential artifacts are as discussed below. Chemical Shift Artifacts Chemical shift is one of the artifacts that may arise during a breast MRI. This artifact occurs at fat-fluid interfaces as a result of differences in resonant frequency of hydrogen present in fat and hydrogen present, especially in water. The hydrogen nuclei in fat resonate at a different frequency compared to water nuclei. The result is the formation of two different chemical artifacts. It has been observed that the first kind of chemical shift artifacts occurs in all MR images as a result of using a frequency-encoding gradient when taking signal measurements. A 224-Hz frequency shift between the fat image and the water image is responsible for the formation of the artifact (Hendrick 2007, p. 195). The bandwidth per pixel of the imaging sequence is the sole determinant of the number of pixels over which the chemical shift will occur. In the case of a chemical shift, a bright or dark band forms perpendicular to the frequency encoding direction in the areas where fat and water face each other. Studies indicate that chemical shifts will always occur on every MR image where water and fat interfaces are present. The best way to reduce the chemical shift artifact is to increase the bandwidth per pixel of the imaging sequence (Hendrick 2007, p. 194). (A) Transaxial and (B) sagittal T2W SE images without fat-saturation. Source: R.E. Hendrick (ed.), Breast MRI: Fundamentals and Technical Aspects. © Springer 2008 (B) Metallic Artifact Metallic artifacts arise when pieces of metal in or around the scanner interfere with the magnetic field. Ferromagnetic metals, which include iron, nickel, and cobalt, are the main causes of inhomogeneity in the magnetic field. Metallic objects that are responsible for causing metallic artifacts include biopsy clips, jewelry, snaps on clothing, and some components of MRI equipment. Non-ferromagnetic metals such as titanium can cause artifacts that distort the image in question. The level of image distortion is determined by the shape and composition of the metallic object. Considerable distortion of the image arises in the presence of surgical clips and percutaneous biopsy clips (Hendrick 2007, p. 196). Ferromagnetic objects disrupt the main magnetic field of the MRI system whenever they are present in the bore of the instrument. The artifacts in this case occur as a result of sudden changes within the magnetic field due to the ferromagnetic objects. This leads to misrepresentation of detected signal. The best way to avoid the occurrence of metallic artifacts is to remove all metallic objects from the patient and the surrounding environment (Hendrick 2007, p. 197). (A) A graph of the signal from overlapping water and fat versus TE. (B) (B) A 1.5 T gradient-echo image of a normal volunteer acquired with TR = 200, TE = 4.4 ms, 256 ? 256 matrix, pixel bandwidth of 81.4 Hz. (C) The same gradient-echo image acquisition as B, but with TE = 7 ms, all other acquisition parameters the same as in B. Source: R.E. Hendrick (ed.), Breast MRI: Fundamentals and Technical Aspects. © Springer 2008 Ghost Artifacts Occurrence of this category of artifacts in MR images is in many cases induced by patients due to the movement of signal-producing tissues during the imaging process. The other cause of ghost artifacts is the instability of equipment within the MR scanner. Motion generates blurred images as well as ghosts of bright moving images. Ghost artifacts arise when the image data is poorly captured or changing values of fixed structures acquired in a different phase encoding views. Ghosting can be prevented by undertaking several measures. One way is to immobilize the breast using breast coils. The other measure undertaken in reduction of ghosting is to reduce the repetition time, but it is not easy in breast MR imaging (Hendrick 2007, p. 187). Transaxial image without fat-saturation showing motion ghosting of fat outside and inside the breasts Source: R.E. Hendrick (ed.), Breast MRI: Fundamentals and Technical Aspects. © Springer 2008 Aliasing Artifacts These types of artifacts occur when some of the signal producing tissues are outside the field of view in either the FE or PE direction. MRI has to undergo a fixed number of FE and PE steps; the inability to perform the required steps leads to the formation of aliasing artifacts. The presence of aliasing artifacts adds structured noise that hinders essential details in the breast as well as presenting false pathology. The artifacts are more common in the PE direction than in the FE direction. Therefore, having more sampling sites on the phase encoding the direction or enlarging the field of view minimizes the occurrence of aliasing artifacts (Hendrick 2007, p. 190). (A) Schematic illustrating aliasing in the PE direction (LR). (B) T2W (STIR) image with patient’s arms by her side and too anterior, causing exterior portions\ of each arm to wrap into the opposite side of the image (arrows), partially obscuring axillary breast tissue. Source: R.E. Hendrick (ed.), Breast MRI: Fundamentals and Technical Aspects. © Springer 2008 RF transmission artifacts Radio frequency artifact is as a result of interference with the transmission of RF signal within the imaging room or the penetration of RF signal through a shield surrounding the imaging unit. Sources of RF signals include radios, television, faulty fluorescent lights, and other electronic monitoring devices. Poor shielding of the RF signals within the imaging room allows the RF signals to leak out and be picked by RF signal receiver coils during imaging. The result is the formation of a noisier background or presence of RF bands at discrete frequencies on the image. RF interference occurs at the center of the image, which makes its detection easy (Hendrick 2007, p. 198). Paying keen attention to background noise in the image helps in minimizing RF interference. The best approach is to acquire phantom images with lights turned on, then off or turning the peripheral equipment within the imaging room on, then off (Hendrick 2007, p. 198). (A) Fat-suppressed contrast-enhanced sagittal image showing a rapidly-enhancing 2-cm invasive ductal carcinoma. (B) Same pulse sequence of the same lesion after placement of an Inrad clip. Source: R.E. Hendrick (ed.), Breast MRI: Fundamentals and Technical Aspects. © Springer 2008 Reconstruction Artifacts These types of artifacts present themselves in the form of repeated pattern of lines or dots at fixed periodicity in planar images. This is as a result of measurements of corrupted data during signal acquisition or alterations before 2DFT or 3DFT image reconstruction. Checking the k-space allows one to correct the corrupted data (Hendrick 2007, p. 200). (A) Vertical line artifact running in the PE (HF) direction is visible in a subtracted contrast-enhanced 3D gradient-echo image.(B) Multiple horizontal lines artifacts running in the PE (LR) direction are visible in this transaxial image due to broadcast radio transmissions into the scan room. Source: R.E. Hendrick (ed.), Breast MRI: Fundamentals and Technical Aspects. © Springer 2008 #2 Clinical usefulness of spectroscopy in Breast MRI Initially, magnetic resonance spectroscopy of the breast was popular in basic research work, but due to advancements in MR techniques, MRS can now be regarded as a common practice in today’s ordinary clinical practices. With the emergence of MR units, which are the SI units, it has now become possible to accumulate useful clinical data. The results obtained from various medical institutions suggest that the application of MRS and MRI techniques will be instrumental in the diagnosis and treatment of breast cancer, in the future (Liberman 2005, p. 7). Magnetic Resonance spectroscopy (MRS) is used together with the breast MRI to provide clinically useful molecular information (Mukherji 1998, p. 177). The underlying principle in the use of MRS is to optimize the use of magnets having higher field strength to separate the diagnostic resonance. Increased availability of 3 T systems has popularized the use of MRS in the diagnosis of breast cancer and monitoring of chemotherapies in breast cancer treatment. Choline metabolites produced in the mammary gland area can be regarded as essential chemical substances that are crucial in the application of proton MRS. In many disease processes, cholines are produced as one of body metabolites since they are among the precursors of phospholipids making up the cell membrane. Their presence in various body organs signifies an increase in the process of membrane synthesis (Torosian 2002, p. 189). In mammary glands, choline is useful in the differentiation of benign and malignant tumors as well as acting as an indicator of tumor viability and activity. In breast cancer research and treatment, much attention on the use of MRS is on differentiating between benign and malignant tumors and monitoring of chemotherapies (Linda and Cecilia 2010, p. 215). In the prediction of chemotherapeutic efficacy, MRS is a novel tool in the evaluation of chemotherapies for the treatment of breast cancer. At the molecular level, it is an essential tool for monitoring the development of breast cancer, as well as early prediction of drug efficacy. Acquiring accurate predictions using MRS is particularly vital in the optimization of chemotherapies and planning for future surgeries. In addition, accurate and the early predictions are vital in reducing the use of unnecessary chemotherapies, which plays a role in reducing adverse effects and speeds up the treatment procedure (Liberman 2005, p. 65). Differential diagnosis is a medical procedure that enables medical experts to come up with a definitive diagnosis by differentiating between two disease conditions. With the help of MRS, benign and malignant breast cancers are easy to identify in order to take the appropriate medical intervention (Ruth and Alan 2001, p. 81). In general, MRS of the breast is a useful tool that can provide essential information using metabolic profile of cancerous breast tissue, which has an elevated choline resonance. However, it is necessary to note that lactating women show elevated choline levels that may give a misdiagnosis. Studies suggest that MRS breast procedures may be useful for younger women. The attainment of reliable results using MRS calls for properly standardized MRS, and carrying out of multicenter collaborative research work (Linda and Cecilia 2010, p. 244). #3 Magnetic Resonance Elastography Palpation is a medical, diagnostic procedure used to differentiate between normal and abnormal tissues using hands. Disease conditions cause changes in the mechanical properties of tissues and these changes can be felt by an experienced hand. Changes that take place during disease conditions vary depending on physiological and pathological states and are vital in the diagnosis of conditions such as breast cancer. However, palpation is only restricted to organs that are easy to feel using hands and is the qualitative diagnostic procedure, whose accuracy relies on the touch sensitivity of the physician (David 2006, p. 23). Numerous imaging techniques such as ultrasonography, computed tomography, and MRI have gained popularity in the medical field, but none of them is capable of detecting changes in mechanical properties of tissues as is done through palpation (Ruth and John 2005, p. 37). The need to have a diagnostic procedure that can detect changes in tissue texture motivated medical researchers to develop a quantitative imaging technique. The resulting technique was then identified as Magnetic Resonance Elastography (Hongen & Eddie 2010, p. 305). Magnetic Resonance Elastography (MRE) is a diagnostic tool that is used in the detection of the elasticity or stiffness of tissues in vivo. The most common application of (MRE) currently is in the study of breast cancer. MRE is a phase-contrast based MRI imaging procedure that is quickly replacing manual palpation in breast cancer screening procedures. The technique employs the use of mechanical waves that examine tissue stiffness quantitatively. Medical experts are regarding MRE as an upgrade on ordinary MRI scanners. The procedure involved with MRE follows three steps. The first step involves the inducement of shear waves that have frequencies ranging from 50-500 Hz into tissues using external drivers. A specific MRI technique is used to image waves inside the body, and the data obtained is processed in order to come with quantitative images that show stiffness of tissue (Ruth and John 2005, p. 147). The most notable advantage of MRE is its ability to obtain accurate measurements on displacements in all the three directions (Hongen and Eddie 2010, p. 313). However, the main problem associated with the use of MRE is the inability to retrieve measurements regarding elasticity from the measured displacements. Areas where MRE has shown significant promise are in palpation by imaging in the detection of tumors, characterization of diseases, and assessment of rehabilitation. In breast cancers, connective tissues proliferate to form a dense layer of fibroblast tissues around malignant breast epithelial cells. This phenomenon brings about the hardening of breast tissue that is felt through manual palpation. These pathological changes in breast cancer are the underlying principles in the design of MRE for quantitative assessment of changes in breast tissues (Jasjit and Rangaraj 2006, p. 300). Therefore, the main idea in using MRI includes performing quantitative analysis on mechanical properties of tissues based on the fact that mechanical properties of tissues may be dramatically affected by various disease conditions. When the procedure is performed during the screening of breast cancer, physicians are able to detect hard masses that present in breast cancer (Ruth and Alan 2001, p. 97). References List David, W. (2006). Breast Cancer, New York, PMPH-USA. pp. 23-170. Hendrick, E. (2007). Breast MRI: Fundamentals and Technical Aspects, New York , Springer. pp. 30-200. Hongen, L. & Eddie, E. (2010). Medical Imaging and Augmented Reality, New York, Springer. pp. 300-315. Jasjit, S. & Rangaraj, R. (2006). Recent Advances in Breast Imaging, Mammography, And Computer-Aided Diagnosis of Breast Cancer, Washington, SPIE Press. p. 300. Liberman, L. (2005). Breast MRI: Diagnosis and Intervention, New York, Spinger. pp. 7-80. Linda, M. & Cecilia, M. (2010). Breast MRI, An Issue of Magnetic Resonance Imaging Clinics, Amsterdam, Elsevier Health Sciences. pp. 215-247. Mukherji, S. (1998). Clinical Applications of Magnetic Resonance Spectroscopy, New York, John Wiley & Sons. p. 177. Ruth, W. & Alan, C. (2001). Breast MRI in Practice, London, Taylor & Francis. pp. 81-98. Ruth, W. & John, B. (2005). Early Breast Cancer: From Screening to Multidisciplinary Management, Second Edition, London, Taylor & Francis. pp. 37-150. Torosian, M. (2002). Breast Cancer, New Jersey, Humana Press. pp. 180-215. Read More