Visibility and artifacts of gold fiducial markers used for image guided radiation therapy of pancreatic cancer on MRI

• Published in: Medical physics (Lancaster) 2015-05, Vol.42 (5), p.2638-2647
• Main Authors: Gurney‐Champion, Oliver J., Lens, Eelco, Horst, Astrid, Houweling, Antonetta C., Klaassen, Remy, Hooft, Jeanin E., Stoker, Jaap, Tienhoven, Geertjan, Nederveen, Aart J., Bel, Arjan
• Format: Article
• Language: English
• Subjects: 60 APPLIED LIFE SCIENCES; Aged; Aged, 80 and over; Biological material, e.g. blood, urine; Haemocytometers; biomedical MRI; cancer; Computerised tomographs; computerised tomography; COMPUTERIZED TOMOGRAPHY; Cone beam computed tomography; Cone-Beam Computed Tomography - instrumentation; Cone-Beam Computed Tomography - methods; Digital computing or data processing equipment or methods, specially adapted for specific applications; Female; FIDUCIAL MARKERS; GOLD; Humans; Hydraulic fracturing; image artifacts; Image data processing or generation, in general; image registration; image‐guided radiation therapy; IN VIVO; Involving electronic [emr] or nuclear [nmr] magnetic resonance, e.g. magnetic resonance imaging; Iron; magnetic fields; Magnetic resonance imaging; Magnetic Resonance Imaging - instrumentation; Magnetic Resonance Imaging - methods; Male; Medical image artifacts; medical image processing; Middle Aged; MRI; NEOPLASMS; NMR IMAGING; PANCREAS; Pancreas - pathology; pancreatic cancer; Pancreatic Neoplasms - pathology; Pancreatic Neoplasms - radiotherapy; PHANTOMS; Phantoms, Imaging; radiation therapy; RADIOTHERAPY; Radiotherapy, Image-Guided - instrumentation; Radiotherapy, Image-Guided - methods; tumours; Visibility
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.4918753

Purpose: In radiation therapy of pancreatic cancer, tumor alignment prior to each treatment fraction is improved when intratumoral gold fiducial markers (from here onwards: markers), which are visible on computed tomography (CT) and cone beam CT, are used. Visibility of these markers on magnetic resonance imaging (MRI) might improve image registration between CT and magnetic resonance (MR) images for tumor delineation purposes. However, concomitant image artifacts induced by markers are undesirable. The extent of visibility and artifact size depend on MRI‐sequence parameters. The authors’ goal was to determine for various markers their potential to be visible and to generate artifacts, using measures that are independent of the MRI‐sequence parameters. Methods: The authors selected ten different markers suitable for endoscopic placement in the pancreas and placed them into a phantom. The markers varied in diameter (0.28–0.6 mm), shape, and iron content (0%–0.5%). For each marker, the authors calculated T2∗‐maps and ΔB0‐maps using MRI measurements. A decrease in relaxation time T2∗ can cause signal voids, associated with visibility, while a change in the magnetic field B0 can cause signal shifts, which are associated with artifacts. These shifts inhibit accurate tumor delineation. As a measure for potential visibility, the authors used the volume of low T2∗, i.e., the volume for which T2∗ differed from the background by >15 ms. As a measure for potential artifacts, the authors used the volume for which |ΔB0| > 9.4 × 10−8 T (4 Hz). To test whether there is a correlation between visibility and artifact size, the authors calculated the Spearman's correlation coefficient (Rs) between the volume of low T2∗ and the volume of high |ΔB0|. The authors compared the maps with images obtained using a clinical MR‐sequence. Finally, for the best visible marker as well as the marker that showed the smallest artifact, the authors compared the phantom data with in vivo MR‐images in four pancreatic cancer patients. Results: The authors found a strong correlation (Rs = 1.00, p < 0.01) between the volume of low T2∗ and the volume with high |ΔB0|. Visibility in clinical MR‐images increased with lower T2∗. Signal shift artifacts became worse for markers with high |ΔB0|. The marker that was best visible in the phantom, a folded marker with 0.5% iron content, was also visible in vivo, but showed artifacts on diffusion weighted images. The marker with the smallest artifact in the p