FieldStrength. Asan Medical Center proves the power of pediatric whole body MRI

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1 FieldStrength Publication for the Philips MRI Community Issue 38 Summer 2009 Asan Medical Center proves the power of pediatric whole body MRI New approaches for pediatric whole body MRI help visualize lesions in children FieldStrength Publication for the Philips MRI Community Issue 38 Summer 2009 Pediatric neuro, MSK, whole body imaging Tokai University reports on benefits of Achieva 3.0T TX with MultiTransmit University of Michigan praises Elite Breast solution for biopsies SmartExam for efficient, reproducible shoulder imaging at PAMF Maastricht performs MRA of spinal cord blood vessels FreeWave upgrade for Intera 1.5T boosts throughput This article is part of Field Strength issue 38, Summer 2009

2 Asan Medical Center proves the power of pediatric whole body MRI New approaches for pediatric whole body MRI help visualize lesions in children Dr. Hyun Woo Goo, Associate Professor of Pediatric Radiology at Asan Medical Center, University of Ulsan, Seoul, Korea has been using whole body MRI techniques for diagnosing lesions in children. According to Prof. Goo, the excellent fat suppression of the center s Achieva 1.5T and 3.0T systems contributes significantly to the effectiveness of these new techniques. Prof. Hyun Woo Goo One of the most important applications for whole body MRI in children is the visualization of suspicious lesions. Whole body MRI offers important advantages, the most obvious being absence of ionizing radiation and excellent soft-tissue contrast especially important for children who may have to undergo many follow-up examinations after malignant lesion diagnosis and therapy. Pediatric MRI also presents some challenges, points out Prof. Goo. It s necessary to adapt many parameters to the patient size. Because the patients are smaller, the signal is less and we have to find the right balance between SNR and spatial resolution to reach the sweet spot. In this respect I find the Philips systems particularly good because the platform is so flexible and it s very easy to trade one parameter off against another to get the right balance. Although scan time is longer, the quality of respiratory-triggered images on the Achieva is almost comparable with that of breath-hold scans. STIR is the workhorse Asan Medical Center performs whole body MRI on Achieva 1.5T and 3.0T systems using the Integrated Body coil. Whole body MRI is mainly used for staging in oncology patients, and for follow up after treatment. But pediatricians have quickly realized that whole body MRI is an effective and easy technique and they also refer patients with other indications, for example multiple hemangiomas or systemic diseases like dermatomyositis, explains Prof. Goo. Even in patients with fever of unknown origin, they often request whole body MRI because they recognize that it s a powerful tool. There are also many motion artifacts with children and you need techniques for suppressing these. Respiratory triggering is one such technique and, here again, the Philips systems perform particularly well. Standard pediatric whole body exam COR and SAG 2D STIR min. Pre-contrast 2D T min. Post-contrast FS 3D T1 3-4 min. Dedicated MRI (DWI, Perfusion ) Total Examination Time min. Prof. Goo regards STIR sequences as the workhorse in whole body MRI in children, since good fat suppression is essential for visualizing lesions, especially extra-skeletal lesions. STIR images have very high contrast-to-noise ratio so can easily visualize small subcutaneous nodules, he says. Our protocol starts with coronal and sagittal STIR which takes 15 to 20 minutes. We also add the sagittal STIR sequence for better imaging of lesions in the sternum and spine. If findings are clear, the examination ends with the STIR scans. If further investigation is needed, precontrast 2D T1-weighted and post-contrast fast 18 FieldStrength Issue 38 Summer 2009

3 1.5T 3.0T STIR DWIBS PET/CT ADC maps Dynamic post-contrast Comparison of 1.5T and 3.0T Due to the higher SNR at 3.0T, image quality is better than at 1.5T. In these 3.0T images, fewer artifacts are observed and very homogeneous signal intensity from the liver, the kidneys and the bowels. T-cell lymphoblastic lymphoma in 14-year-old girl Several sites of lymphoma can clearly be seen both in whole body MRI and PET/CT (blue circled). In addition, the coronal STIR image shows an additional hepatic lesion (pink circled), which appears benign on PET/CT. ADC map demonstrates an increased ADC value of the hepatic lesion which is not typical of lymphoma. Dynamic CE T1-weighted MR images are confirmed as benign hemangioma. suppressed 3D T1-weighted scans follow. T1-weighted sequences, which are sensitive to fat, are particularly suitable for adolescents because their bones contain a lot of fatty marrow, says Prof. Goo. T1-weighted imaging is also used to delineate localized fatty marrow changes after radiotherapy and to identify subacute hemorrhage. Finally, dedicated sequences such as DWI or contrast-enhanced imaging may be performed. The STIR sequence is very sensitive but may be less specific. Adding a DWIBS scan is then a very good choice to increase specificity, mentions Prof Goo as an example. The total exam time can thus vary from 15 to about 60 minutes. New approaches for pediatric whole body MRI Prof. Goo and his colleagues at the Asan center have been evaluating alternative ways for performing pediatric whole body MRI to improve SNR and spatial resolution. They have developed a new sliding-coil technique using the tabletop extender and the 16-channel Torso XL coil to provide full-body coverage in 3 stations of children up to 125 cm in length. Even though the 32-channel Body coil covers the whole of the body, pediatric patients usually feel uncomfortable with it. In contrast, with the sliding coil technique, patients feel much more comfortable because the 16-channel coil simply slides over the patient s body, he points out. Recently, Prof. Goo has also started using the Achieva 3.0T for whole body MRI. In general, the RF issues that may occur with adults at 3.0T are largely absent in pediatric patients, so pediatric imaging fully benefits from the higher SNR at 3.0T. Prof. Goo compared 1.5T and 3.0T results using the Integrated Body coil. It s not surprising that we found 3.0T images to have a clearly better SNR. We also saw fewer artifacts and improved homogeneity at 3.0T when we chose a patient with a left-right diameter of less than 45 cm, he says. The better image quality was particularly noticeable in the liver, kidney and bowel areas. FieldStrength 19

4 STIR STIR Bone scintigraphy DWIBS Rhabdomyosarcoma in 8-year-old girl The bone scintigraphy images (right) look entirely normal, while MRI shows a focal hyperintense lesion in the lower thoracic spine. The two suspicious lesions also stand out from the background very clearly in the DWIBS image. 10-year-old with lymphoma Pre-treatment Whole-body DWIBS PET DWIBS DWIBS ADC STIR provides more detail than corresponding PET images. Follow up after 9 days induction chemotherapy shows that the lymphoma involvement is markedly reduced. The very dark nodules involving both kidneys have almost disappeared on the follow up ADC map. ADC maps also show that the bone marrow signal has changed from black to white, which is not conspicuous on STIR images. 20 FieldStrength Issue 38 Summer 2009

5 Whole body MRI in staging and follow-up exams Children with metastatic tumors often have to undergo all kinds of imaging in a short period of time, and the Asan team tries to find ways to limit the number of exams and the exposure to ionizing radiation. Prof. Goo and co-workers compared whole body MRI with bone scintigraphy in pediatric patients with malignant solid tumors or Langerhans cell histiocytosis (LCH). Their studies showed significantly better sensitivity for whole body MRI, which supports the conclusions from studies in other centers. In our center we now direct children towards whole body MRI instead of bone scintigraphy, asserts Prof. Goo. The case of whole body MRI versus PET/CT is not so clear cut. Whole body MRI is generally preferred for brain, liver and bone marrow, while PET/CT is preferred for lungs and lymph nodes. Further comparative studies are necessary, but Prof. Goo believes that the two modalities will continue to complement each other. Other strategies Prof. Goo points out that some aspects of whole body MRI require attention. Some believe that whole body MRI is not useful for lung evaluation, but we frequently do see lung nodules on STIR images even if these are very small, says Prof. Goo. Artifacts caused by metallic implants may also hinder image interpretation, but when using STIR, we don t experience this as a problem. However, whole body MRI, particularly STIR, may not always be specific enough so it is important to use additional information, he explains. Prof. Goo makes use of all clinical data available, including clinical history, lesion distribution pattern, findings from other imaging methods, and results from dedicated regional MRI and diffusion/perfusion MRI. DWI, in particular is valuable for initial and follow-up imaging. Finally, we often use whole body DWIBS, a very robust sequence with low distortion and excellent fat suppression. Spatial resolution is also very high in DWIBS images, so you can see more detail than with PET, he says. A growing trend Prof. Goo believes that the number of pediatric whole body MRI examinations will increase in the future driven by the concerns regarding children s exposure to ionizing radiation. In addition, new technical developments like the use of the SENSE Head Spine coil and the slidingcoil technique for whole body imaging of children at Asan both leading to improved SNR and spatial resolution are likely to further spur the growth of pediatric whole body MRI. After 9 days chemotherapy DWIBS ADC STIR References HW Goo, SH Choi, T Ghim, HN Moon, JJ Seo Whole-body MRI of paediatric malignant tumours: comparison with conventional oncological imaging methods Pediatric Radiology (2005) 35: HW Goo, DH Yang, YS Ra, JS Song, HJ Im, JJ Seo, T Ghim, HN Moon Whole-body MR Imaging of Langerhans Cell Histiocytosis: Comparison with Plain Radiography and Bone Scintigraphy Pediatric Radiology (2006) 36: T Takahara, Y Imai, T Yamashita, S Yasuda, S Nasu, M Van Cauteren Diffusion Weighted Whole Body Imaging with Background Body Signal Suppression (DWIBS): Technical Improvement using Free Breathing, STIR and High Resolution 3D Display Radiation Medicine, 22(4), (2004) FieldStrength 21