Whole body MRI with DWIBS in oncology: an overview of imaging findings

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1 Whole body MRI with DWIBS in oncology: an overview of imaging findings Poster No.: C-2622 Congress: ECR 2013 Type: Educational Exhibit Authors: E. J. Boerhout, D. P. Noij, I. C. Pieters, E. F. I. Comans, J. S. Regelink, S. Zweegman, R. de Bree, J. A. Castelijns; Amsterdam/ NL Keywords: Metastases, Diagnostic procedure, MR-Functional imaging, MRDiffusion/Perfusion, MR, Oncology, MR physics DOI: /ecr2013/C-2622 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 18

2 Learning objectives To provide an overview of the physical principles of diffusion-weighted imaging (DWI) and diffusion-weighted whole-body imaging with backgroundbody-signal-suppression (DWIBS). To illustrate the potential and spectrum of imaging findings in whole body MRI including DWIBS in a series of oncologic patients. To outline the pitfalls of DWIBS. Background 18 Whole-body (WB) -MRI has been introduced as an alternative to F-FDG-PET/CT in routine clinical imaging, having proved its usefulness for the evaluation of patients with lymphoma, multiple myeloma [1] and a series of other malignancies, including lung [2], colorectal [3], breast [4] and renal cancer [5]. In several studies, WB-MRI shows a promising role for the evaluation of metastases, with detection rates similar to PET/CT (Table 1). 18 F-FDG- Physical principles of diffusion-weighted imaging (DWI) In addition to 'conventional' T1 and T2 WB-MRI, DWI and/or diffusion-weighted wholebody imaging with background-body-signal-suppression (DWIBS) has the potential to provide functional information [12-14]. DWI allows visualization of the random (Brownian) extra-, intra- and transcellular motion of water molecules [15] and therefore correlates with cellular density, which is characteristically increased in malignant tumors. DW images are usually obtained by adding two motion probing gradients (MPG's) in an echo-planar sequence. In stationary tissues the phase shift by the first MPG is nullified by the second MPG and therefore no MRI signal is attenuated. However, in water molecules freely moving in one voxel there will be a change in orientation of the spins of water molecules during MR data acquisition and cause phase shifts. Because of the resulting phase dispersion the MRI signal is attenuated [12]. The amount of diffusion weighting is determined by the b-value and is dependent (amongst others) on the strengths and duration of the MPG's. A higher b-value (e.g. 1000) is important to exclude the effects of microperfusion [13]. DWI in body imaging Page 2 of 18

3 DWI has since long proved its use in imaging of the brain. However, to use this technique in extracranial imaging several difficulties had to be overcome, such as: disturbing movements by respiration and bowel movements; heterogeneity of tissues with abrupt air-tissue and bone-tissue boundaries; magnetic susceptibility artifacts; relatively long acquisition time in which breath hold was not possible. Technological improvements, such as ultrafast single-shot echo-planar imaging (EPI), parallel imaging, and advances in MR-gradient technology made acquisition of DWI with high b-value in the body possible. In 2004 Takahara et al. [14] developed DWIBS. This sequence is performed in a freebreathing state and uses high b-values and hence suppresses most of the background signal [17]. The axial source DWI-images are reconstructed in the coronal plane and the gray-white scale is inverted. The feasibility of DWIBS in free breathing is explained in the concepts of intravoxel incoherent motion IVIM (diffusion) and intravoxel coherent motion IVCM (bulk tissue motion, e.g. respiration). In short, by a combination of IVIM and IVCM diffusion-weighted image contrast may be maintained with only slight image blurring. The reason why IVCM does not affect diffusion-weighted image contrast is the fact that the acquired phase shift of coherently moving water molecules is equal in each phase-encoding step and, therefore does not affect image formation. Since respiratory motion can be regarded as coherent motion during the small period in which the two gradients are applied (usually < 50 ms), DWI under free breathing is feasible. [15] The use of DWIBS in WB-MRI protocols has yet been studied by several authors, providing high sensitivity compared to metastases [18-22]. 18 F-FDG-PET/CT for the detection of distant WB-MRI with DWIBS, protocol design Ever since WB-MRI has shown its potential for the evaluation of certain malignancies, a multitude of studies and research questions have been addressed. Even though the term 'whole body' is usually reserved for imaging of the entire body in the coronal plane, several other sequences in variable planes are also being used. So far, no consensus exists concerning the optimal scanning protocol for whole body imaging. The parameters of DWIBS in our institution are listed in Table 2. Images for this section: Page 3 of 18

4 Table 1: An illustration of overall sensitivity and specificity of whole body MRI compared to PET-CT in literature. SCC = squamous cell carcinoma.* Depending on site (lung, musculoskeletal or lymph nodes). Page 4 of 18

5 Table 2: Scanning parameters in DWIBS in VU University Medical Center. SPAIR: Spectral Adiabatic Inversion Recovery, Grappa: Generalized Autocalibrating Partially Parallel Acquisition Page 5 of 18

6 Imaging findings OR Procedure details Examples of the potential of DWIBS in a series of oncologic patients See Figs Pitfalls of DWIBS: possible false positive findings An important pitfall in DWIBS is that not only malignant tumors show diffusion restriction. Lymph nodes Normal lymph nodes have a relatively restricted diffusion because of their high cellular density. Metastatic lymph nodes have increased cellular density and may have necrotic areas. However it is still unknown whether it is possible to differentiate benign lymphadenopathy from malignant nodes using DWIBS [12, 13, 18]. (See Fig. 5). Normal tissues with high signal on DWIBS Besides lymph nodes, also some other tissues represent high signal in DWIBS, like the brain, spinal cord, peripheral nerves, salivary glands and tonsils, adrenals, spleen, gallbladder, kidneys and ureters, intestines, bone marrow, testes and prostate. To prevent misinterpretation of these areas with T2 penetration effect and missing obscured lesions in these areas, DWIBS should be combined with an anatomical sequence. (See Figs. 6 and 7). Distortion The 2D EPI acquisition type sequence is very sensitive for heterogeneities in the magnetic field, causing distortion. These artifacts occur mainly in air-soft tissue and soft tissue-bone boundaries, e.g. in the lower neck, shoulders and around the lung apices [15]. This is seen in virtually all patients. This stresses the importance of correlation with the anatomic MR images. (See Figs. 6 and 7). Artifacts due to moving organs Artifacts due to movement of imaged organs may occur, mainly around the diaphragm and bowel. Abnormalities on the coronal reconstructed DWIBS images should always be compared to anatomic MR images to differentiate lesions from artifacts. If it is an artifact, Page 6 of 18

7 the axial DWI b-1000 images (source image for DWIBS) may sometimes be helpful to further characterize the artifact. (See Fig.8). Pitfalls of DWIBS: possible false negative findings Around heart and diaphragm Another difficulty of DWIBS is the area around the heart and diaphragm, because of movement of organs. In these areas small lesions can easily be missed. Lungs Detection of lung metastases may be challenging with WB-DWIBS, mainly due to a lower resolution compared to CT. Wang et al. reported a detection rate of 76.9% of DWIBS, compared to 94.9% with PET-CT for the evaluation of nodular lung lesions [18]. A higher susceptibility to breathing artifacts and less tissue contrast between lung parenchyma and mediastinal structures in WB-MRI and/or DWIBS may be the reason why DWIBS 18 may be inferior to F-FDG-PET-CT. Furthermore, thinner slices can be performed in the CT protocol compared to the MRI examination [11]. (See Fig. 9). Images for this section: Page 7 of 18

8 Fig. 1: a.t1, b.stir and c.dwibs in a 16-year old boy with Hodgkin lymphoma stage IIa. WB-MRI with DWIBS showed pathological cervical lymph nodes on the right. Note the diffuse high signal of the spine and scapula (arrowheads). At these sites no increased 18F-FDG uptake was observed and these foci were interpreted as physiological or reactive (due to treatment). Page 8 of 18

9 Fig. 2: Section of WB-MRI: a.stir, b.dwibs and c.fused 18F-FDG-PET-CT in a 15year old girl with Hodgkin lymphoma stage IV. Chain of extensive pathological lymph nodes around the aorta are well seen on STIR and DWIBS (arrows), in correlation with 18F-FDG-PET. Page 9 of 18

10 Fig. 3: 59-year-old man with cervical lymphadenopathy (arrows) of squamous cell carcinoma (unknown primary location). Section of WB-MRI: a.t1, b.stir and c.dwibs. The parotid glands also show physiological signal on DWIBS (arrowheads). Page 10 of 18

11 Fig. 4: a.t1, b.stir and c.dwibs in a 71-year old man with several multiple myeloma lesions in pelvis. Fig. 5: 70 -year old female with squamous cell carcinoma of the tongue base. a.t1, b.stir and c.dwibs of a section of WB-MRI show lymph nodes of normal size (up to 7 mm short axis). Page 11 of 18

12 Fig. 6: 56-year old man with recurrent squamous cell carcinoma of the tongue base. a.t1, b.stir and c.dwibs. Slightly high signal of the bone marrow on DWIBS, without any detectable bone lesions on T1. Note physiological signal in the brain, spleen (arrowhead), kidneys and sigmoid (arrowhead) on DWIBS. In addition, there is a heterogenic signal intensity in the spleen due to moving of the diaphragm. Note high signal because in airtissue boundaries (arrows). Page 12 of 18

13 Fig. 7: a.t1 and b.dwibs of a selected area of the neck in a 58- year old man with nasopharyngeal squamous cell carcinoma. Physiological signal in cervical nerve roots (arrows) and spinal cord on DWIBS. Increased signal around the lung apices and lower neck due to air-tissue interface of the lungs and therefore based on artifacts, create the impression of extensive pathological lymph nodes, which are not detected on T1. Page 13 of 18

14 Fig. 8: Artifact near the diaphragm in a 15- year old girl with Hodgkin lymphoma stage IV. a.t1, bstir, c.dwibs, d.axial DWI b-1000 (source image for DWIBS) and e.fused 18F-FDG-PET-CT image. The right paravertebral high signal on DWI just below the diaphragm on DWIBS (arrow) was not identified on anatomic MR-images and 18F-FDGPET-CT. Possibly this artifact is due to movement, although the cause of this artifact is not entirely clear. Page 14 of 18

15 Fig. 9: a.t1, b.stir and c.dwibs of a selected area of the chest in a 63- year old man with a pulmonary metastasis in the left upper lobe of recurrent nasopharynx carcinoma. Note upper thoracic artifacts due to distortion. Page 15 of 18

16 Conclusion WB-MRI with DWIBS seems feasible for use as a screening and staging method in the evaluation of oncologic disease. The evaluation of the DWIBS sequence entails the understanding of certain pitfalls, which may lead to either false-positive or false-negative findings. Also, the reading of whole-body scans may initially be challenging for the reading radiologist due to the interpretation of images acquired in the coronal plane rather than axially; and the increased amount of incidental findings. Further studies are needed in order to reach consensus on optimal (often tailor-made) scanning protocols. References Regelink JC, Minnema, MC, Terpos E, et al. Comparison of the diagnostic accuracy and detection rate of modern and conventional imaging techniques in establishing multiple myeloma related bone disease: a systematic review. British Journal of hematology, in press Ohno Y, Koyama H, Onishi Y, et al. Non-small cell lung cancer: whole-body MR examination for M-stage assessment-utility for whole-body diffusionweighted imaging compared with integrated FDG PET/CT. Radiology 2008;248(2): Schmidt GP, Baur-Melnyk A, Haug A, et al. Whole-body MRI at 1.5 T and 3 T compared with FDG-PET-CT for the detection of tumour recurrence in patients with colorectal cancer. European Radiology 2009;19(6): Schmidt GP, Baur-Melnyk A, Haug A, et al. Comprehensive imaging of tumor recurrence in breast cancer patients using whole-body MRI at 1.5 and 3 T compared to FDG-PET-CT. European Journal of Radiology 2008;65(1):47-58 Platzek I, Zastrow S, Deppe PE, et al. Whole-body MRI in follow-up of patients with renal cell carcinoma. Acta radiologica 2010;51(5):581-9 Ng SH, Chan SC, Yen TC, et al. Pretreatment evaluation of distantsite status in patients with nasopharyngeal carcinoma: accuracy of whole-body MRI at 3-Tesla and FDG-PET-CT. European Radiology 2009;19(12): Yi CA, Shin KM, Lee KS, et al. Non-small cell lung cancer staging: efficacy comparison of integrated PET/CT versus 3.0-T Whole-body MR imaging. Radiology 2008;248(2): Plathow C, Aschoff P, Lichy MP, et al. Positron emission tomography/ computed tomography and whole-body magnetic resonance imaging in staging of advanced nonsmall cell lung cancer-initial results. Investigative Radiology 2008;43(5):290-7 Chan SC, Wang HM, Yen TC et al. ¹#F-FDG PET/CT and 3.0-T whole-body MRI for the detection of distant metastases and second primary tumours Page 16 of 18

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18 22. Kim JK, Kim KA, Park BW, et al. Feasibility of diffusion-weighted imaging in the differentiation of metastatic from nonmetastatic lymph nodes: early experience. Journal of Magnetic Resonance Imaging 2008;28(3): Personal Information Page 18 of 18