Design of a multimodal (1H MRI/23Na MRI/CT) anthropomorphic thorax phantom: Initial results at 3 T
Wiebke Neumann1, Florian Lietzmann1, Lothar R. Schad1, and Frank G. Zöllner1

1Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany


Anthropomorphic phantoms are an essential tool for the validation of image registration algorithms of multimodal data and are important for quantification experiments in 1H and 23Na MR imaging. A human thorax phantom was developed with insertable lung, liver, rib cage modules and tracking spheres. Evaluation regarding the tissue-mimicking characteristics with 1H and 23Na MR and CT imaging shows that the modules possess T1, T2 and HU values comparable to those of human tissues. This work presents an MR- and CT-compatible phantom which allows experimental studies for quantitative evaluation of deformable, multimodal image registration algorithms and realistic multi-nuclei MR imaging techniques.


Image-guided interventions rely on real-time imaging and the fusion of data sets with previous images acquired by CT and MRI. Image registration algorithms have to take up various challenges such as varying resolutions, slice thicknesses and altered patient positions between the different acquisitions. Anthropomorphic phantoms for validation of algorithms under near real-world conditions serve as an important additional stage between geometric phantoms and in vivo studies.

Methods and Materials

The anthropomorphic thorax phantom consists of four main modules placed in an acrylic case that can be flooded with water for MR imaging (Fig. 1).

A lung module is built from two breathing bags (volume of 2 l each) filled with cubical natural rubber foam (side length 5 or 20 mm). Inflation can be performed manually by a connected resuscitator. Inferiorly, a movable diaphragm is retracted by rubber bands and causes deflation of the breathing bags.

Two balloon-shaped liver modules (weight 1500 g each) are filled with distilled water. Approximate tissue parameters are achieved by further adding 2.37 ppm gadoterate meglumine (T1 modifier), 1.3 % agarose (T2 modifier), 3 % carrageenan (mechanical stabilizer) and 0.03 % sodium azide (preservative) based on Hattori et al.1 Na+ concentration was set to 20 mM.2 Several spherical inserts representing tumors (30 mm diameter) were added to one of the liver modules. Na+ concentrations of the inserts were varied in a physiological range (30/40/80/154 mM Na+).

Two rib cage modules can be inserted on top of lung and liver modules. They either consist of artificial ribs (dimension 15×10×200 mm3) made of epoxy (structural support) and 19.6/39.2 % CaCO3 (HU modifier) or porcine ribs.

Isometric tracking spheres consisting of an MR visible sphere (30 mm diameter) enclosed by a CT visible shell (40 mm diameter) were also designed (Fig. 2).

CT data were acquired with a Somatom Force (Siemens Healthcare, Erlangen) using a convolution kernel Br36d (kVp=110 kV). A ROI-based HU analysis with ImageJ was conducted. CT images were rendered to 3D volume data sets using ITK software.3 The motion of the diaphragm was evaluated at two positions during five breathing cycles.

MR imaging was performed on a 3 T whole-body scanner (Magnetom Skyra, Siemens Healthcare, Erlangen) with a 16-channel body coil using turbo spin echo sequences (TE=[15, 30, 40, 50, 60, 120, 240] ms, TI=[250, 500, 800, 1000, 2000, 5000] ms, 2.3 mm resolution, 300×300 mm2 FOV). T1 and T2 relaxation times were obtained by pixel-wise fitting. 23Na imaging was performed with a double-resonant transmit receive array using a density-adapted three-dimensional radial gradient echo sequence (TR=100 ms, TE=0.49 ms, 4.0 mm resolution, 348×348 mm2 FOV, 10000 spokes) as presented by Haneder et al.4

Results and Discussion

The HU values of the lung filling (-801 to -668 HU) are comparable to human lung tissue5 and depend on the state of compression of the foam cubes similar to human lungs. The diaphragm moves 26 mm on average during breathing cycles which is in accordance with literature values (18.8 mm to 38.2 mm).6 The liver filling has a T1 relaxation time comparable to human liver (measured 790±28 ms, literature 812 ms 6) with a relative standard deviation of 3.5 % (Fig. 3). The T2 relaxation time is larger than human liver values (measured 65±1 ms, literature 42 ms 7, Fig. 3). However, the T2 relaxation time is adjustable during future construction by increasing the agarose concentration. Spherical inserts representing tumors are well distinguishable in 1H and 23Na MR imaging (Fig. 4). HU values of the artificial ribs (218±56 HU/339±121 HU) are comparable to human bone4 and offer a simple geometric structure suitable for registration algorithm validation. Porcine ribs are geometrically more complex and essential for near-realistic bone imitation. The tracking spheres are well detectable in both CT and MRI and serve as multimodal landmarks. The parameters of the tracking speres can be adjusted in the following ranges to receive a distinct signal: HU value from 150 HU to 900 HU, T1 relaxation time from 550 ms to 2000 ms, T2 relaxation time from 40 ms to 200 ms.


This work proposes an anthropomorphic multimodal thorax phantom which fulfills the demands of a simple, inexpensive system with interchangeable modules. It enables experimental studies for quantitative evaluation of multimodal, dynamic and deformable image registration as well as multi-nuclear MR imaging techniques. The modular design permits to complement the present setup with additional modules. In the future, this phantom will be used for validation of quantitative MR measurements (perfusion, density, diffusion) which is in line with current developements for reliable and comparable data in addition to diagnostic images.


This research project is part of the Research Campus M²OLIE and funded by the German Federal Ministry of Education and Research (BMBF) within the Framework “Forschungscampus: public-private partnership for Innovations” under the funding code 13GW0092D.


1. Hattori et al. Development of MRI phantom equivalent to human tissues for 3.0-T MRI. Med Phys. 2013 Mar;40(3):032303

2. James et al. In vivo sodium MR imaging of the abdomen at 3T. Abdom Imaging. 2015 Oct;40(7):2272-80

3. Yushkevich et al. User-guided 3D active contour segmentation of anatomical structures:Significantly improved efficiency and reliability. Neuroimage. 2006 Jul 1;31(3):1116-28

4. Haneder et al. Quantitative and qualitative (23)Na MR imaging of the human kidneys at 3 T: before and after a water load. Radiology. 2011 Sep;260(3):857-65

5. Kalender, W. A. Computertomographie. Publicis Corporation Publ. 2006

6. Hanley et al. Deep inspiration breath-hold technique for lung tumors: the potential value of target immobilization and reduced lung density in dose escalation. Int J Radiat Oncol Biol Phys. 1999 Oct 1;45(3):603-11

7. Stanisz et al. T1, T2 relaxation and magnetization transfer in tissue at 3T. Magn Reson Med. 2005 Sep;54(3):507-12


Figure 1: Pictures of the phantom. Top: Breathing bags are connected to a manual resuscitator. The porcine rib cage is laid on top of the lung and liver module. Bottom left: Side view of the phantom with the lung, liver and artificial ribs modules visible. Bottom right: Top view of the phantom. The breathing bags and the liver module are attached to the diaphragm. The artificial ribs are inserted on top.

Figure 2: Construction of tracking spheres. Top left: MR visible sphere. Top right: CT visible shell. Top middle: Schematic drawing of the MR visible sphere (dashed-red) enclosed by the CT visible shell (blue). Bottom left: T1 weighted image with a visible gelatineous MR core. Bottom right: CT image with the CT shell clearly distinguishable. Two tracking spheres at different locations are depicted, images were cropped for better visualization.

Figure 3: Top row: T1 map of the liver modules. Bottom row: T2 map. Left column: Homogeneously filled liver module. Right column: Additional spherical inserts representing tumors with varying Na+ and T1 and T2 modifier concentrations were inserted in one liver module. Images were cropped for better visualization.

Figure 4: MR images acquired with double-resonant 1H/23Na transmit receive array: Left: T1- weighted proton image (flash2D, TR=140 ms, TE=2.27 ms) of a transverse slice of the liver module with additional spherical inserts representing tumors. Right: 23Na MR image of the corresponding slice. Red arrows indicate the corresponding positions. Images were cropped for better visualization.

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)