Contact

Paul Chang

Address: Spemannstr. 41
72076 Tübingen
Room number: 3.A.02
Phone: +49 7071 601 938
Fax: +49 7071 601 702
E-Mail: Paul.Chang

 

Picture of Chang, Paul

Paul Chang

Position: PhD Student  Unit: Henning Scheffler

Background

 

Mechatronics engineer specialising in control systems and digital electronics. Projects undertaken thus far include:

  • image processing in magnetic resonance imaging (MRI);
  • controller design with applications in fractional and integer proportional-integrator-differentiator (PID) controllers;
  • software development for pH chemical sensing platforms.

 

Motivation

 

The magnetic eld strengths of magnetic resonance imaging (MRI) systems have been increasing since the MRI was first invented. The reason for thisupward trend in eld strength is the expected increases in:

  • signal-to-noise ratio (SNR);
  • blood oxygen level-dependent (BOLD) contrast; and
  • spectral resolution.

Despite the benefits of higher field strengths, there are also a number of drawbacks. One of these drawbacks is the decrease in the homogeneity of the B0 (main static) field. This degrades all of the potential benefits that can be gained at higher field strengths.

This project aims to homogenise the B0 field in real-time using a feedback system with field monitoring.

 

2015-02-09

Real-time Feedback B0 Shim System for Ultra-high Field MRI

 

Overview


The aim of this project is to improve current dynamic shim updating (DSU) methods which will be done by using a feedback system to control the shims based on field measurements.

 

By using a feedback system the cross-coupling between the shim coils, eddy currents induced by shim coils and disturbances in the static field due to physiological artifacts will be be compensated. The control system needs to switch shim coil currents quickly and efficiently and be robust against noise and disturbances.

 

Dynamic Shimming

 

RRI shim amplifiers

Shim coils generate a set of 3D basis functions (typically spherical harmonic functions) to produce the required field.

Static shimming sets the shim terms before the measurement and these remain the same during the measurement. Dynamic shimming is the process of shimming while using different shim terms for each slice (or voxel) that is being measured at the time.

This requires developing a robust algorithm that calculates the spherical harmonic function. This software application needs to provide a user-friendly interface for defining regions of interest (ROIs) and calculating shim terms.

Dynamic shimming requires amplifiers that can be dynamically changed and for this purpose the Resonance Research Inc. MXW 28ch shim amplifiers are used. These include spherical harmonic functions up to the 4th order and partial 5th and 6th order functions.

 

Field Monitoring

 

Field cameraTo implement a feedback system we require a hardware to monitor the B0 field. This is done using a custom built field camera which consists of an array of field probes. This setup is used to characterise the shim system and to monitor the actual field during experiments.

 

The field probes produces free induction decay (FID) signals which have frequencies related to the strength of the field at that position. Hence, these probes can be used to measure the magnetic fields. The measurements are sensitive to the positions of the probes and therefore the positions need to be accurately determined for reliable measurements.

 

Controller

 

Embedded system - ZynqThe controller used for the real-time feedback system is implemented on an embedded system for fast digital control. This was preferred over an analogue implementation because digital controllers are more flexible.

 

The field monitoring system data is input into the controller and compared with the set-points (which are the desired shim terms calculated from the B0 shim algorithm). The data are processed and the controller outputs are then sent to the gradient and shim amplifiers.

 

Linux penguinThe controller is implemented on a system-on-chip Zynq 7020 board. This provides FPGA functionality to interface with custom Siemens gradient system communications, as well as a dual-processing system which provides access to common communication protocols and easier software design. An asymmetric multiprocessor (AMP) is implemented running Linux on one core and a standalone program on the other core.

 

system overview

Current

Max Planck Institute of Biological Cybernetics

2013-Current

Control/MR Engineer (PhD Student)

High-field Magnetic-Resonance Group

PhD in Neural and Behavioural Science

Graduate Schoolof Neural and Behavioural Science

Project: Real-time Feedback B0 Shim System for Ultra-high Field MRI

 

Education

1) Imperial College London

2011-2012

MSc in Control Systems

Department of Electrical Engineering

Thesis: Development of Versatile Software for Chemical Sensing Applications

 

2) University of Cape Town

2007-2010

BSc (Eng) in Mechatronics

Department of Electrical Engineering

Other Majors: Mathematics and Economics

Thesis: Combination of functional and structural MRI with rapid prototyping as a neurosurgical tool

 

3) Westville Boys' High School

2002-2006

 

Publications/Conference Papers

 

1) "The dual role of Parylene C in chemical sensing: Acting as an encapsulant and as a sensing membrane for pH monitoring applications" in Sensors and Actuators B: Chemical 2013


2) "Sensing H+ with conventional neural probes" in Applied Physics Letters 2013


3) "Free-standing Parylene C films as flexible pH sensing membranes" in IEEE Sensors Conference 2013


4) "Preoperative Three-Dimensional Model Creation of Magnetic Resonance Brain Images as a Tool to Assist Neurosurgical Planning" in Stereotactic and Functional Neurosurg 2013


5) "Comparison of PI and FPI Controllers on a Hydraulic Canal using Pareto Fronts" in CISSE 2012


6) "Combination of Functional and Structural MRI with Rapid Prototyping as a Neurosurgical Tool" in ISMRM 2011


7) "Programming Styles for an Open Source Epanet Project" in WDSA 2010

 

Work Experience

1) University of Cape Town

2011

Academic Course Tutor

Description: Tutored undergraduate courses. This involved academic and lab assistance and marking coursework.

 

2) Open Box Software

2010 (2 months)

Intern Software Developer

Description: Vacation work as an informations system software developer. Involved website development and writing software for the back-end database.

 

3) Stone Three Venture Technology

2009 (2 months)

Intern Engineer

Description: Vacation work that involved building hardware to froth analyzers. Writing software applications for in-house use.

 

3) Altech UEC

2007 (2 months)

Intern Engineer

Description: Vacation work that involved writing in-house software applications as well as testing hardware devices.

Preferences: 
References per page: Year: Medium:

  
Show abstracts

Articles (3):

Chang P, Nassirpour S and Henning A (March-2017) Modeling real shim fields for very high degree (and order) B0 shimming of the human brain at 9.4 T Magnetic Resonance in Medicine Epub ahead.
Nassirpour S, Chang P and Henning A (December-2016) High and ultra-high resolution metabolite mapping of the human brain using 1H FID MRSI at 9.4T NeuroImage Epub ahead. in press
Trantidou T, Payne DJ, Tsiligkiridis, V, Chang Y-C, Toumazou C and Prodromakis T (September-2013) The dual role of Parylene C in chemical sensing: Acting as an encapsulant and as a sensing membrane for pH monitoring applications Sensors and Actuators B: Chemical 186 1-8.

Conference papers (2):

Chang Y-C, Avdievich N and Henning A (August-2014) System Identification and Signal Processing for PID Control of B0 Shim Systems in Ultra-High Field Magnetic Resonance Applications, 19th World Congress of the International Federation of Automatic Control (IFAC 2014), International Federation of Automatic Control, New York, NY, USA, IFAC Proceedings Volumes, 47(3), 7517-7522.
pdf
Handwerker J, Ortmanns M, Anders J, Eschelbach M, Chang P, Henning A and Scheffler K (November-2013) An active TX/RX NMR probe for real-time monitoring of MRI field imperfections, IEEE Biomedical Circuits and Systems Conference (BioCAS 2013), IEEE, Piscataway, NJ, USA, 194-197.

Posters (13):

Nassirpour S, Chang P and Henning A (April-27-2017): Comparison of different acceleration methods for high-resolution metabolite mapping using 1H FID MRSI at 9.4T, 25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017), Honolulu, HI, USA.
Chang P, Nassirpour S and Henning A (April-26-2017): Decoupling Controller Design for Real-time Feedback of B0 Shim Systems, 25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017), Honolulu, HI, USA.
Chang P, Nassirpour S and Henning A (April-26-2017): Dynamic B0 Shim Controller for Digital Pre-emphasis with Sub-millisecond Update Rate, 25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017), Honolulu, HI, USA.
Chang P, Nassirpour S and Henning A (April-26-2017): Flexible General-Purpose Embedded System for Real-time Feedback and Dynamic B0 Shimming, 25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017), Honolulu, HI, USA.
Chang P, Nassirpour S and Henning A (April-25-2017): Limitations of NMR Field Cameras for B0 Field Monitoring, 25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017), Honolulu, HI, USA.
Chang YC, Nassirpour S, Fillmer A and Henning A (May-10-2016): Correcting Geometric Distortion in B0 Mapping, 24th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2016), Singapore.
Chang YC, Nassirpour S and Henning A (May-10-2016): Very high order B0 Shimming of the human brain at 9.4 T considering Real B0 Shim Fields, 24th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2016), Singapore.
Chang P, Nassirpour S and Henning A (March-2016): Very High‐order B0 Shimming for Single‐Shot EPI at 9.4 T in the Human Brain, ISMRM Workshop on Ultra High Field MRI: Technological Advances & Clinical Applications, Heidelberg, Germany.
Chang P, Eschelbach M, Syha R, Scheffler K and Henning A (June-2-2015): Impact of Gradient Nonlinearity on the Accuracy of NMR Field Camera Readouts, 23rd Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2015), Toronto, Canada.
Eschelbach M, Chang YC, Handwerker J, Anders J, Henning A and Scheffler K (June-2-2015): Tracking Motion and Resulting Field Fluctuations Using 19F NMR Field Probes, 23rd Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2015), Toronto, Canada.
Shao T, Avdievich NI, Chang P, Hoffmann J, Scheffler K and Henning A (June-1-2015): Systematic investigation of influence factor on parallel transmit pulse performance at 9.4 Tesla, 23rd Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2015), Toronto, Canada.
Chang Y-C, Eschelbach M, Avdievitch N, Scheffler K and Henning A (May-15-2014): Fast Method for Parametric System Identification of Gradient Systems, Joint Annual Meeting ISMRM-ESMRMB 2014, Milano, Italy.
Chang Y-C, Eschelbach M, Scheffler K and Henning A (May-12-2014): Hybrid Digital Phase-Locked Loop and Moving Average Filtering Improves SNR in Spatio-Temporal Field Monitoring, Joint Annual Meeting ISMRM-ESMRMB 2014, Milano, Italy.

Talks (7):

Chang P, Nassirpour S and Henning A (April-27-2017) Abstract Talk: Fast non-water suppressed metabolite cycled 1H FID MRSI at both 3T and 9.4T, 25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017), Honolulu, HI, USA(1250).
Nassirpour S, Chang P and Henning A (April-27-2017) Abstract Talk: High resolution maps of individual macromolecule components in the human brain at 9.4T, 25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017), Honolulu, HI, USA(1059).
Nassirpour S, Chang P and Henning A (April-27-2017) Abstract Talk: Pushing the limits of ultra-high field MRSI: benefits and limitations of 9.4T for metabolite mapping of the human brain, 25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017), Honolulu, HI, USA(1248).
Nassirpour S, Chang P and Henning A (April-26-2017) Abstract Talk: Multi-slice metabolite mapping with Very-High Degree Dynamic B0 Shim Updating at 9.4T using Accelerated 1H FID MRSI, 25th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2017), Honolulu, HI, USA(0971).
Chang P (August-16-2016) Abstract Talk: Very High-Order B0 Shimming for Ultra-High Field Magnetic Resonance, ISMRM Workshop on MR Spectroscopy: From Current Best Practice to Latest Frontiers, Allensbach-Hegne, Germany.
Nassirpour S, Chang YC, Fillmer A and Henning A (May-13-2016) Abstract Talk: A Comparison of Optimization Algorithms for Localized in-vivo B0 Shimming, 24th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2016), Singapore(1142).
Eschelbach M, Loktyushin A, Chang P, Handwerker J, Anders J, Henning A, Thielscher A and Scheffler K (May-10-2016) Abstract Talk: A Comparison of 19F NMR Field Probes and an Optical Camera System for Motion Tracking, 24th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2016), Singapore(0340).

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Last updated: Tuesday, 18.11.2014