Angiogenesis studies have continuously evolved over the last years. The advent of macromolecular contrast agents allows for the maintenance of such agents for longer periods in the intravascular spaces. Contrast media containing gadoxetic acid are examples of such agents in the characterization of focal liver lesions. The development of substances directed against molecules expressed by neoangiogenic vessels, as the factor of endothelial vascular growth, is another application field by the perfusion technique 16 , Magnetic resonance spectroscopy MRS evaluates the distribution and levels of metabolites normally found in healthy tissues as well as increased levels of metabolites usually detected in within tumor Creatine, choline, lactate, citrate, N-acetyl aspartate and adenosine triphosphate are examples of altered metabolites which are commonly found This technique can be indicated, for example, to evaluate breast, prostate and brain lesions 18 — The main indications of this method are the following: lesion characterization, selection of biopsy site, and evaluation of therapeutic response, among others.
This technique can be applied in the evaluation of brain lesions. Increased levels of choline considered a marker for cell proliferation in association with decreased levels of creatine considered a marker for energetic processes and decreased levels of N-acetyl aspartate considered a neuronal marker have been found in the evaluation of brain neoplasms.
Combining such levels, it is possible to differentiate, for example, low-grade from high-grade gliomas 18 , 19 Figure 8. It can differentiate viable tumor from necrotic area important in the evaluation of the tumor response. In the presence of response, a decrease in the choline and N-acetyl aspartate peaks is observed in association with increased levels of lipids and lactate anaerobic markers Figure 8. A year-old male patient.
Tumor resection glioblastoma multiforme in the left temporal lobe six months ago, undergoing treatment with radiotherapy and temodal. MRI scan with advanced techniques was requested for differential diagnosis between recurrence and radionecrosis in post-gadolinium enhancement areas in the surgical site. On A, one observes contrast-enhanced T1-weighted image demonstrating enhancement of the surgical site arrow.
On C and D , the spectroscopy study demonstrates decreased peak of the metabolite N-acetyl aspartate NAA and increased choline peak Cho , corroborating the diagnosis.
How clinical imaging can assess cancer biology | Insights into Imaging | Full Text
In the evaluation of breast lesions, for example, association with choline peak may be detected in malignant lesions. However, in benign lesions or in healthy breast tissues, choline levels are either low or undetectable. In the evaluation of the prostate spectroscopy obtains metabolic data based on the relative concentration of endogenous metabolites such as choline, creatine, citrate and, most recently, polyamine Thus, spectroscopy may be employed in the diagnosis of tumor recurrence, in patients treated by radiotherapy, cryotherapy or surgery 21 — The routine utilization of spectroscopy in the evaluation of other neoplasms is still questionable Figure 9.
Figure 9. On B , T2-weighted image demonstrates a subtle ill defined area arrow. On D , the ADC map demonstrates the same area with low signal intensity arrow at 6 o'clock in the peripheral zone. On E , the dynamic contrast-enhanced image demonstrates enhancement in the medial region from 5 o'clock to 7 o'clock. On F , the kinetic curve presents intense and early enhancement washin tending towards rapid clearance washout. Such parameters represent an area suspected for malignancy. Whole-body imaging modalities have been utilized for some time in the evaluation of cancer patients However, the development of new MRI sequences has been improving the utilization of the method in the evaluation of cancer patients The introduction of echo-planar techniques has allowed the acquisition of whole-body images by means of different sequences such as T1-weighted, T2-weighted, STIR and diffusion.
The better management of the effects from artifacts generated by physiological cardiac and respiratory motion has allowed for the acquisition of good functional images which supplement morphological data usually obtained by conventional MRI techniques Figure 10 Figure WBMRI is useful in the detection of metastases, particularly in brain, liver and bone lesions. On this figure, a year-old female patient presenting with lung adenocarcinoma in the upper right lobe long arrow with metastasis to the left adrenal gland short arrow.
Whole-body MRI WBMRI is a noninvasive technique free from the risks of ionizing radiation and with high resolution for soft tissues, which can rapidly acquire whole-body images. During the scanning, the body is divided into different portions, and the images are acquired in axial and coronal sections Diffusion-weighted whole-body imaging may be applied to obtain images with body signal suppression.
Thus, many organs have their signals removed and the tumor areas with diffusion are identified as intensely bright or with high signal intensity 27 , Studies in the literature have demonstrated that WBRMI is superior to scintigraphy in the detection of bone metastases as it allows for the visualization of bone marrow infiltration, while bone scintigraphy can only detect the osteoblastic activity 28 — It is a quite sensitive method for assessing bone lesions in cases of multiple myeloma, as it allows for the direct evaluation of bone marrow involvement by the tumor.
Usually, it is more sensitive than computed tomography in the evaluation of disease activity. Additionally, it can be employed in the monitoring of the treatment effectiveness and in the prediction of the treatment response and prognosis Moreover, WBMRI is also very useful in the detection of distant metastases, especially to the brain, liver and musculoskeletal system Figure 11 Such tool may be also applied to evaluate patients with metastases without a known primary tumor. Because of the absence of ionizing radiation risks, is a good option for early detection tumors in asymptomatic individuals, when the disease is still curable A year-old male patient presenting with a solid and spiculated mass in the right upper lobe, incidentally detected at radiography and with histological diagnosis of adenocarcinoma.
Biopsy confirmed the diagnosis of pulmonary adenocarcinoma metastasis. However, the method presents some limitations such as contraindication for exposure to magnetic fields. The limitations in the evaluation of the lung parenchyma and the long acquisition time are being overcome with the development of more advanced apparatuses and new techniques.
Nowadays, a WBMRI scan can be completed in 30 minutes, with satisfactory resolution of the chest structures and with the capability of screening peripheral lesions. Additionally, WBMRI may become a useful tool for patients who do not want to be exposed to ionizing radiation or for those patients on whom the effects of radiation might cause severe injuries, such as pregnant patients, children or patients who have been repeatedly exposed during treatment Currently there is no consensus about which sequences combination provides greater WBMRI accuracy, while maintaining reasonable time efficiency Notwithstanding the following types of sequences are normally utilized:.
A fast STIR sequence with a typical echo train length between 16 and 30 may be utilized either alone or in combination with other types of sequences The advantages of STIR imaging include the fact that most pathological tissues are rich in protons and have prolonged T1 times and prolonged T2 relaxation times, with consequential high signal intensity on STIR sequences Fat suppression with STIR images is stronger and more homogeneous than fat saturation on T2-weighets images. Coronal T1-weighted fast spin echo sequences are particularly useful in the evaluation of alterations secondary to radiation therapy and metastatic lesions in the fatty marrow Contrast-enhanced sequences allow for the study of a region in a single breathhold.
The liver, for example, can be evaluated in the arterial and venous phases. At the end, the rest of the body can be evaluated for screening metastatic lesions The utilization of gadolinium-based contrast agents improves the sensitivity, specificity and diagnostic accuracy of the method.
Its utilization facilitates the combination of local staging and evaluation of metastatic disease in a single scan. It has a short acquisition time and may be easily incorporated in the WBMRI protocol, without compromising time efficiency of the method. This type of sequence provides good morphological data and outlines vessels with good accuracy. The chest and abdominal imaging provided by the WBMRI is particularly challenging due to respiratory motion and intestinal peristaltic motion. These may be obtained applying respiratory compensation techniques with extended acquisition time.
Antiperistaltic drugs could help to reduce the intestinal motility. It is important to note that in cases where the chest or the abdomen are the location of a primary tumor or area of neoplastic disease, the WBMRI scan is generally performed according to a dedicated imaging protocol including the utilization of respiratory compensation techniques and, sometimes, the administration of antiperistaltic drugs.
Clinical applications of PET/MRI in oncology: Opportunities and challenges
A limitation that impaired the association of both modalities in a single facility was the fact that the photomultipliers utilized in PET did not operate appropriately within or near the magnetic field. However, with technological developments obtained in the recent years, some of those barriers were overcome and the first facilities now are available for clinical application Furthermore, the advantage of comprehensively scanning the whole body in a single moment would justify the combined utilization of both tools.
However, a consensus on the indications and actual benefits in clinical practice is still to be established. We currently live in the era of individualized treatment. Genetic and intrinsic factors of the tumor are decisive in the evolution of the disease and in the therapeutic approach.
The evaluation of functional parameters by MRI is increasing in the clinical set of cancer patients allowing a better understanding of the disease complexity and therapeutic management, with a positive impact on such group of patients. Oncologic imaging endpoints for the assessment of therapy response. Recent Pat Anticancer Drug Discov.
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Other malignancies: Malignant melanoma. Du kanske gillar. Spara som favorit.
Skickas inom vardagar. In the new era of functional and molecular imaging, both currently available imaging biomarkers and biomarkers under development are expected to lead to major changes in the management of oncological patients. This two-volume book is a practical manual on the various imaging techniques capable of delivering functional information on cancer, including diffusion MRI, perfusion CT and MRI, dual-energy CT, spectroscopy, dynamic contrast-enhanced ultrasonography, PET, and hybrid modalities.
This second volume considers the applications and benefits of these techniques in a wide range of tumor types, including their role in diagnosis, prediction of treatment outcome, and early evaluation of treatment response.