MRI AND PET/CT imaging in the Early and late Stage Disease - Essay Example

? MRI AND PET/CT imaging in the Early and late Stage Disease Introduction Magnetic resonance Imaging is a type of test that makes use of the energy of the radio wave pulses and magnetic field to make pictures of structures and organs inside the body. CT, MRI AND PET imaging can be devoted for establishing means of increasing the acquisition speed. It is worth noting, therefore, that impressive gains have been realized in an effort to make MRI and PET more effective in their application. Recent studies have shown that MRI and PET has become part of the current and most impressed technology. This paper seeks to provide an overview of fundamental and potentials of non-invasive imaging modalities for prostate carcinoma which include CT, and MRI. This is with a view to highlight specific and sensitive imaging modality often used as guiding interventions for controlling diseases. With most studies indicating that the increase in cancer cases is attributed to PCa, this paper seeks to evaluate the effectiveness of non-invasive screening modalities aforementioned underpinning it to the diagnosis of PCa and the radiation therapy planning. The focus, therefore, is to investigate the features of imaging modalities alongside various screening techniques combined with their usefulness in radiation therapy planning. Theory According to Weishaupt eta l. (2004) parallel imaging has many applications. As used in the medical field, the parallel imaging is extensively used to provide varying information concerning body structures that can easily be seen using computed topography scan, ultrasounds and X-rays. MRI can also indicate problems that might not be seen using other imaging methods. In doing MRI test, the section of the body under study is often placed in a special machine containing a strong magnet. Most pictures from the MRI scan can easily be reviewed remotely. On the contrary, when using CT contrast materials might be used during the process of conducting the scan. This helps in showing certain structures somewhat more clearly. In this case, there are various reasons as to why it is used. In order to achieve good quality data for diagnosis it is vital to use a modality which has high specificity and sensitivity. As suit can be expected adequate demonstration of the carcinoma is valuable for therapy selection and further clinical management. For the detection of primary PCa the specificity of CT is limited. The major advantage of CT is its inability to give adequate data for the differentiation between benign and malignant tissue. On the other hand, MRI are somewhat more reliable than PET/CT when dealing with tumor. Studies have indicated that combined technique of imaging modalities such as PET/CT has a limited sensitivity for the detection of primary PCa. However, PET/CT has be described as being most sensitivity and speci?city in detectiing primary PCa. This is attributed to the fact that less differentiate carcinomas do not have significant glucose uptake and therefore is somewhat challenging to have early prostate carcinomas detected using PET/CT. It has also been shown that Fluorodeoxyglucose (FDG) and acetate PET techniques do not have the ability of distinguishing between malignant and benign PCa. There are various reasons for doing MRI test. As often is the case, it is used in establishing problems such as injury, infection, tumors, and internal bleeding. It might also be done for purposes of getting more information concerning a problem observed on the X-ray, CT scan and ultrasound. In this case, MRI and PET/CT are used to investigate the brain for bleeding inside the brain, aneurysm, tumors, nerve injury, and problems such as damages caused by stroke. CT/PET and MRI scans can also be used to establish problems associated cancer. According to Wintersperger, BJ, et al. (2003) CT can generate both coronal, as well as sagittal views used in countering of target organs and volumes, which are at risk. But the CT, and MRI can yield sagittal and coronal views, and produces somewhat better discrimination of some tissue often known to be valuable for RTP. This way, CT/PET and MRI can be used in moderating normal tissue complications. Research has also shown that CT/PET and MRI can be used in decreasing of acquisition time, reducing higher signal to noise ratio (SNR), providing more images per patient for more diagnostic information, and for purposes of providing minimal SAR (problem with high-field MR). This is attributed to the materials often used. In this regard, the presence of protocol/ pulse for sequence optimization, incorporation of faster image reconstruction hardware, and use of single element coil helps in increasing the SNR. It also increases acquisition time, and causes reduction in the tissue proximity (Bammer & Schoenberg, 2004). This is hinged on the fact that Parallel imaging works on the basic principle of collecting a signal with various coils placed at different points around the volume of interest (Maki eta l., 2004). This implies that each coil receives a signal from an area having different intensity. As such, the sensitivity information arising from the phased array coils is used to replace the spatial encoding steps that were normally carried out by the magnetic field gradients. As noted, it is only recently that techniques of parallel imaging were commercialized, and therefore, a vast field of clinical applications is being explored. While being used in clinical applications, it helps in improving spatial resolution, and in reducing the acquisition time (Parizel et al., 2003). Through this, it becomes possible to achieve faster image acquisition especially when there is a reduction in the number of encoding steps. While this is done, contrast and spatial resolution are maintained at a given level. It is also noted that with reduced scan time and increased temporal resolution, a predetermined spatial resolution can help in enhancing the spatial resolution within the given imaging time (Itskovich, et al. 2004). There is also a reduction in the artifacts effects given the time dependent effects. Moreover, CT, and MRI is used in reducing the artifacts susceptibility within the EPI sequences. This way, it makes them to shorten the echo train length. The occurrence of trade off is common when using, MRI and PET/CT. This is because a decline in the number of the phase encoding steps leads to reduction in the SNR and the overall reconstruction process in the parallel imaging (Hahn, eta l., 2003). It advantages are such that a reduced number of the phase encoding lines results to a shorter scan time as well as aliasing in the final image By and large, Parallel imaging as a family of techniques, was developed to take advantage of spatial information, which is common in most phased-array of the radio frequency coils. As often used, they reduce acquisition times especially in the magnetic resonance imaging. The sampled k-space lines get reduced in parallel imaging, by a factor 2 or even greater. Through this, they help shorten the acquisition time. In most clinical applications, there is reduction of acquisition time, and the improved spatial resolution. The speed of imaging has been attributed to the gradient slew rates (Bammer & Schoenberg, 2004). As such, the last decade has seen significant improvements in gradient speed and operation of the MRI and PET scanners which at the moment reach highest limit possible. Considering the fact that, the peripheral nerve stimulation is affected by fast switching magnetic fields, and then excess dense RF-pulses have the potential to cause tissue eating (Scheidegge & Besieger, 1999). According to Sodickson (1997) MRI helps in incorporating the sensitivity profiles as the basis for the generation of spatial harmonics and the subsequent reconstruction of the image within the Fourier domain. Specifically the missing k-space lines are reintroduced prior to the Fourier transform. It is worth noting that partial acquisition is a variant. In the case off method there is an addition of a small number of the k-space during acquisition. This helps in eliminating the need for a separate coil acquisition. As a matter of fact, the CT reconstruction algorithm provides improvements in the SNR and elimination of some artifacts attributed to CT. In a study conducted by Pruessmam (2004) it has been shown that there exists an alternative image based MRI. In this method, there is Fourier transformation of data leading to aliased images. Images, as observed in this method, are unwrapped through the use of the spatial information within the coil sensitivity profiles. Generally, CT and MRI are the most widely used methods. For the MRI method, the scan time is directly related with the number of the encoding phase steps and subsequent incorporation of multiple coils makes it easier to reduce the sampling density. This can be illustrated as shown below. However, there is a considerable increase in the distance between the phase encoding lines. It is also worth noting that reduced sampling density implies that Nyqvist criterion is not satisfied, hence the use of the Fourier transformed image. In (a) it can be observed that, with accurate coil sensitivity maps, the MRI reconstruction obtains the best possible result with an optimized SNR. The Grappa reconstruction is an fundamentally an approximation to MRI reconstruction. However, on the visual scale, there is no different between the two. As widely cited, the availability of MRI technique has made it to be used for clinical application. Its ability to produce higher image reconstruction, as well makes it to be the most preferred. For instance, in cardiac imaging reduction in scan time, the MRI relaxes the requirements for breath hold studies (Kuhl, et al., 2003). The gain in scan time can also be used for purposes of improving spatial resolution, reducing imaging time and real time cardiac imaging. MRI is also applied in the contrast enhanced magnetic resonance angiography. This way, it allows a higher spatial resolution at a constant time (Hu, 2004). However, image reconstruction of a single shot EPI is somewhat problematic considering that in the EPI images and sensitivity maps differ (Weiger, 2000). On the other hand, Grappa employs the regenerative k-space technique. It is advantageous in the lung and abdominal MRI and PET/CT, and real time imaging (Huber, et al., 2004). CT technique is particularly employed in areas where the coil sensitivity maps are difficult to obtain, especially in homogenous areas such as the lungs and the abdomen. In such areas determination of precise spatial coil sensitivity is difficult. As such, algorithm provides a good quality image reconstruction in the absence of the sensitivity maps. In addition, the k space lines are fit to calculate the reconstruction parameters which involve procedure concerning the global information. It is, therefore, not affected by localized in homogeneities (Lederman, 2003). It can also be noted that k-sspace lines ensures that accurate information is available to realize good reconstruction quality. The figure below illustrates this scenario CT technique can also be used in a single shot EPI since the k space based reconstruction of the missing lines is not affected by distortions in the image (Barkhausen, 2004). Generally, CT has shown robust reconstruction without modification of the EPI or the reconstruction algorithm as shown below. In many applications only a small region within the object is relevant for a diagnosis. This implies that by choosing a smaller FOV than the object, the irrelevant parts of the image would have its imaging speed increased even in the absence of parallel imaging. However, full FOV images may result into erroneous coil sensitivity maps, leading to image artifacts after reconstruction. Following that the MRI method has to use a larger FOV to prevent the aliasing of tissue from the outside. On the other hand, MRI technique has the capability to generate partially aliased image construction having the same appearance as in the conventional imaging without modification of the reconstruction algorithm. The difference between CT and MRI can be seen in the appearance of the artifacts where the sense reconstruction is performed in the image domain on a pixel by pixel basis. In this case, non ideal conditions in the reconstruction process leads to local noise enhancement. In most cases, it appears localized in a folded image. On the contrary, MRI generates the missing K-space lines in which an inaccurate calculation of the missing lines produces aliasing artifacts in the reconstructed image which can be seen entirely over the reconstructed image FOV Today, the choice of the optimal parallel imaging techniques is limited by the commercial availability of the said methods. The choice between the image domain, CT and the self calibrating k-space technique depends upon a number of factors. For instance, if the speed is of importance, then having an extra self calibrating k space may seem to be disadvantageous and thus CT stands out as the method to choose. Notably, it is a concern for low resolution images because of the reduction in the K space lines when the image matrix increases. It should also be noted that CT provides a slightly higher image quality when used with high acceleration factors (Boesiger, 2002). MRI is preferred in situations where accurate sensitivity maps are difficult to obtain, such as the lungs since it provides a more robust reconstruction (Griswold & Jakob, 2002. Auto calibration technique may also be preferred in situations where patients have a difficulty in respiration a reproducible manner thus leading to discrepancies between the parallel image acquisition and the calibration acquisition which in turn results to reconstruction artifacts (Wintersperger, et al. 2003). However, the acquisition time must be within the patients breath hold capacity. The choice of CT over MRI also depends on the FOV. Where, in the MRI like image based techniques when full FOV becomes small as compared to object, formation of artifacts occurs in the reconstructed image. To overcome this, aliasing is avoided in the reconstructed image. On the contrary, CT can generate partial aliased reconstructed image having no artifact to allow for the selection of a smaller FOV in situations where spatial resolution is a key consideration. Early diagnosis of neoplasm can assist in the eradication of the development prior to its spread. This is based on the nature of neoplasm and the model upon which it spreads in the body. The aspect of early diagnosis is based on the probability of arresting the spread of the disease prior to the realization of the metastasis stage. The aim of apprehending the activity of cancer cells can be achieved with ease if the cells are undergoing the initial division sages prior to their involvement in the metastasis level where they are distributed or transported randomly in the body. However, the task of quantifying the presence of a given line of cells in the cancer cells can be a task of increased demand since it involves the identification of unique markers that may not be presented in such quantifiable quantities during the initial stages of malignant cancer. The development of equipments that can assist in early diagnosis of cancer cells can be of significant contribution to the development of the intermediate options of arresting subsequent progress. The impact of the symptoms that are associated to some specific models of neoplasm are rather cumbersome to detect at an early stage. This implies that their detection may be achieved while it is too late and the symptoms have already spread to the rest of the organs. This may best exemplified via the reflection of the prostate cancer, a model of neoplasm that seems to be gender sensitive, in that it mainly affect men. The detection of prostate cancer in an early stage can be described as an effort out of vanity if some methods are considered. This is based on the specific qualities if prostate cancer as compared to other models of cancer. Irrespective of being associated with the malignant cancer model, the disease indicates little symptoms in its initial stage. This implies that its detection is based on the results achieved from the examinations of the symptoms as they may seem in the molecular field. The molecular approach of diagnosis follows various routes, namely the quantification of the precise antigens related to prostate cancer or the examination of the related markers that may be associated to the disease. This implies that the prospect of evaluating the presence of this disease may be improved via these methods. On the other hand, physical examination may be used to analyze the occurrence of the disease. The utilization of the molecular approaches may be rather biased in terms of quantification since they are not efficient in low production of the anticipated markers. This leaves the options for early quantification to be based on the findings of the visualization methods. This method seek to identify the prostate glands and offer a visual insight on their development and behavior. They are termed as the best models of real time diagnosis of neoplasm in visible organs. MRI is listed amongst the most novel of ideas that have contributed growly to the improvement in the visual diagnosis. Magnetic resonance imaging (MRI) focuses on the utilization of active but short magnetic radiation sin the development of visual images about an organ. Such images are developed in accordance to the specifications of interest as desired by the physician. In addition, the MRI diagnostic system is less harmful to the patient, as compared to other diagnostic models that utilizes radiations. The eventual outcome of this tool of diagnosis is the development of a wide visual image on the organs that are around the prostate glands. This identifies it for utilization in the quantification of the spread of the disease, as compared to other visualization techniques. In conclusion, CT is not a significantly effective for screening modality diagnostic purposes, but however it plays a fundamental role in RTP. Radiotherapy planning without CT features would be misrepresentative of what is pragmatically happening within the patient’s soma. Accordingly MRI has a substantial ability of excellent delineation of structures. MRI can be potentially used for diagnostic purposes without any issues arising. PET is also a useful screening modality that can be used with the intention of enhancing the accuracy of both diagnosis and RTP of PCa. However it would be arguable to say that a single modality can give enough data with regards to radiotherapy purposes. Multimodality screening techniques are certainly more reliable for visualizing bodily structures with high accuracy. However further clinical screening trials need to be conducted in order to identify the optimal screening technique for prostatic carcinomas. References Bammer,R., Schoenberg, O, 2004. Advances in Clinical Parallel Magnetic Resonance Imaging. Magnetic Resonance Imaging; 15(3): 129–158. Barkhausen, J. 2004. 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