Radiofrequency fields in hyperthermia and MRI

152 Pages·2006·13.93 MB·English

Radiofrequency fields in
hyperthermia and MRI
Exploiting their similarities for mutual benefit
Nico van den Berg
ii
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Radiofrequency fields in
hyperthermia and MRI.
Exploiting their similarities for mutual benefit.
“Radiogolven in hyperthermie en MRI.”
Wederzijds profijt van hun electromagnetische overeenkomsten.
(met een samenvatting in het Nederlands)
Proefschrift ter verkrijging van de graad van doctor aan de
Universiteit Utrecht
op gezag van de Rector Magnificus, Prof. dr. W.H. Gispen
ingevolge het besluit van het College voor Promoties
in het openbaar te verdedigen
op dinsdag 26 september 2006 des middags te 2:30 uur
door
Cornelis Antonius Theodorus van den Berg
geboren op 15 juli 1975 te IJsselmuiden.
promotor: Prof. dr. ir. J.J.W. Lagendijk
Faculteit der Geneeskunde, Universiteit Utrecht
co-promotor: dr. ir. L.W. Bartels
UMC Utrecht
co-promotor: dr. J.B. van de Kamer
AMC Amsterdam
Het beschreven werk werd verricht op de afdeling Radiotherapie van het Univer-
sitair Medisch Centrum Utrecht, participerend in het Image Sciences Institute en
deonderzoekschool voor biomedische beeldwetenschappen, ImagO, in eendoor de
NederlandseKankerbestrijdinggefinancierdproject(UU2001-2462).Dezeuitgave
is tot stand gekomen met financi¨ele steun van de Nederlandse Kankerbestrijding,
het ImagO en Philips Medical Systems BV, Best, the Netherlands.
Contents
1 Introduction 3
1.1 General introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Regional Hyperthermia Treatment Planning . . . . . . . . . . . . . 5
1.3 Quality assurance in regional hyperthermia . . . . . . . . . . . . . 8
1.4 Quality assurance of radiofrequency fields with MRI . . . . . . . . 8
1.5 Optimizing radiofrequency fields in MR imaging . . . . . . . . . . 10
1.6 Outline of this thesis . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2 Feasibility and accuracy of 3D quantitative blood flow mapping
of the prostate using dynamic contrast-enhanced multi-slice CT 15
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.2 Materials and Methods. . . . . . . . . . . . . . . . . . . . . . . . . 18
2.2.1 Patients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.2.2 DCE-CT imaging and analysis . . . . . . . . . . . . . . . . 18
2.2.3 Determination of the confidence intervals . . . . . . . . . . 20
2.2.4 Calculation and analysis of the parameter maps. . . . . . . 21
2.3 Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.3.1 Determination of the confidence intervals . . . . . . . . . . 22
2.3.2 DCE-CT imaging . . . . . . . . . . . . . . . . . . . . . . . . 25
2.3.3 DCE-data analysis . . . . . . . . . . . . . . . . . . . . . . . 27
2.3.4 Analysis of the parameter maps . . . . . . . . . . . . . . . . 28
2.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3 Patient Specific Thermal Modelling of the Prostate. 33
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.2 Materials and Methods. . . . . . . . . . . . . . . . . . . . . . . . . 36
3.2.1 Dynamic Contrast Imaging . . . . . . . . . . . . . . . . . . 37
3.2.2 Discrete Vessel Model of Pelvis . . . . . . . . . . . . . . . . 38
3.2.3 Computation of Power Density . . . . . . . . . . . . . . . . 40
3.2.4 Thermal Modelling . . . . . . . . . . . . . . . . . . . . . . . 40
3.2.5 Comparison with Clinical Data . . . . . . . . . . . . . . . . 42
v
vi Contents
3.2.6 Discrete Vessel Model of Prostate Vasculature. . . . . . . . 42
3.3 Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.3.1 Perfusion Maps . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.3.2 Temperature Calculations . . . . . . . . . . . . . . . . . . . 45
3.3.3 Comparison with Clinical Data . . . . . . . . . . . . . . . . 45
3.3.4 Pre-heating in Prostate Vessels . . . . . . . . . . . . . . . . 46
3.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
3.4.1 Prostate and Tumour Perfusion . . . . . . . . . . . . . . . . 48
3.4.2 Impact of Perfusion Maps on Thermal Calculations. . . . . 48
3.4.3 Pre-heating: An issue or not? . . . . . . . . . . . . . . . . . 49
3.4.4 Comparison with Clinical data . . . . . . . . . . . . . . . . 52
3.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
4 Experimental validation of hyperthermia SAR treatment plan-
+
ning using MR B imaging 55
1
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
4.2 Materials and Methods. . . . . . . . . . . . . . . . . . . . . . . . . 59
4.2.1 Phantom . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4.2.2 MR measurements . . . . . . . . . . . . . . . . . . . . . . . 60
4.2.3 FDTD model of the transmit coil . . . . . . . . . . . . . . . 61
4.3 Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.3.1 Measurements . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.3.2 Simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
4.3.3 Comparison measurements and simulations . . . . . . . . . 67
4.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
4.4.1 Comparison Measurements and Simulations . . . . . . . . . 68
4.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
+
5 The use of MR B imaging for validation of FDTD electromag-
1
netic simulations of human anatomies. 71
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
5.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
5.2.1 Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . 73
5.2.2 Error analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 74
5.2.3 FDTD model of transmit coil.. . . . . . . . . . . . . . . . . 75
5.2.4 Generation of dielectric patient model . . . . . . . . . . . . 76
5.3 Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
5.3.1 Measurements . . . . . . . . . . . . . . . . . . . . . . . . . 77
5.3.2 Simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
5.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
+
5.4.1 B measurement . . . . . . . . . . . . . . . . . . . . . . . . 79
1
5.4.2 Comparison the measurements and simulations . . . . . . . 81
5.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Contents 1
6 The design of a fully integrated regional hyperthermia - 3 Tesla
MRI system for the treatment of pelvic tumours. 85
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
6.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
6.2.1 Design proposal and FDTD simulations . . . . . . . . . . . 88
6.2.2 Evaluation of hyperthermia performance . . . . . . . . . . . 89
6.2.3 Evaluation of the MRI performance . . . . . . . . . . . . . 89
6.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 92
6.3.1 Hyperthermia performance . . . . . . . . . . . . . . . . . . 92
6.3.2 MRI performance. . . . . . . . . . . . . . . . . . . . . . . . 93
6.3.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
+
7 Simultaneous B homogenization and SAR hotspot suppression
1
using an MR phased array transmit coil. 97
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
7.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
7.2.1 Coil simulation . . . . . . . . . . . . . . . . . . . . . . . . . 100
7.2.2 Elliptical Phantoms . . . . . . . . . . . . . . . . . . . . . . 100
7.2.3 Patient Model . . . . . . . . . . . . . . . . . . . . . . . . . 101
7.2.4 Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . 101
7.3 Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
7.3.1 Elliptical Phantoms . . . . . . . . . . . . . . . . . . . . . . 102
7.3.2 Human Anatomies . . . . . . . . . . . . . . . . . . . . . . . 105
7.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
7.4.1 Field patterns for quadrature excitation . . . . . . . . . . . 107
7.4.2 Phase/amplitude optimization. . . . . . . . . . . . . . . . . 109
7.4.3 Applying elliptical settings as generic settings . . . . . . . . 111
7.4.4 Combination and comparison with other techniques . . . . 112
7.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
8 Summary and general discussion 115
8.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
8.2 General discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
9 Samenvatting 123
10 Publications 129
11 Dankwoord 133
12 Curriculum Vitae 135
References 137

Chapter 1
Introduction
1.1 General introduction
Hyperthermia aims to elevate the temperature of malignant tissue to the range
of 40 to 44 oC. It is being applied as an adjuvant therapy to radiotherapy and
chemotherapy. The biological rationale was established by several investigations
in the eighties that demonstrated that heat leads to a sensitisation of tumours
to radiation and chemotherapeutic drugs (Dahl, 1988; Dewhirst et al., 1983). In
addition, it was shown that hyperthermia above 41-42 oC has a direct cell-killing
effect (Dewey, 1994). The beneficial effects of hyperthermia were confirmed by
several clinical trials (Overgaard et al., 1995; Vernon et al., 1996; Van der Zee
et al., 2000).
Deep-seated pelvic tumours such as prostatic and cervical tumours are treated
by radiofrequency (RF) waves in the frequency range of 70 to 150 MHz (Wust
etal.,1995).Thistypeofhyperthermiaisreferredtoasregionalhyperthermia.In
regional hyperthermia the goal is to concentrate the heat deposition in the target,
while keeping the energy deposition in healthy tissue under control. A popular
applicator design with good performance in this respect is the annular phased
array antenna (Turner, 1984; Sullivan et al., 1992; Wust et al., 1996; Paulsen
et al., 1999). See Figure 1.1 for an example. It allows conformal heating patterns
by maximizing the constructive interference of the antenna electric fields with
amplitude and phase control. In this way target temperatures up to 43 oC can be
reached (Kroeze et al., 2001).
In the clinical practice a temperature goal of 43 oC is rarely achieved and realis-
tic temperatures vary mostly in the range of 40 to 41 oC (Hand et al., 1997). A
fundamentalandmajorcauseforthistemperatureunderdosageisthatinregional
hyperthermiaarterialbloodentering theheatedvolume isatarelatively low tem-
perature of 38 to 39 oC (Van Vulpen et al., 2003). This leads to the creation of
coldtractsinthetargetvolumearoundnon-thermallyequilibrateddiscretevessels
3
4 Chapter 1. Introduction
(Crezee and Lagendijk, 1992; Lagendijk et al., 1995). A further cause of tempera-
ture heterogeneity is the heterogeneous power absorption by the anatomy due to
the large contrast in dielectric tissue properties (Wust et al., 1999; Van de Kamer
et al., 2002a)
To gain insight into the complex electromagnetic and thermal processes that gov-
ern the temperature distribution in the target volume, hyperthermia treatment
planning has been developed (Lagendijk, 2000; Wust et al., 1996). The planning
comprises of electromagnetic and thermal modelling techniques which are used to
calculatethespecificabsorptionrate(SAR)andtemperaturedistribution(Vande
Kamer et al., 2001a). The planning determines in individual patient cases the set
of antenna amplitudes and phases that maximizes the thermal dose in the target
andminimizes toxicity (Kroezeetal.,2001). Themostimportant difficulty ofthis
concept is that it assumes that a whole range of technical factors and clinical un-
certainties can be verified and controlled accurately during treatment. In practice
such an ideal control is nearly impossible to accomplish with the current limited
quality assurance techniques.
Another application of hyperthermia treatment planning is the electromagnetic
and thermal analysis of MR imaging. Due to technical challenges high field MR
imaging faces with respect to RF field inhomogeneities and RF safety, this matter
has become a lively research topic (Jin et al., 1996; Ibrahim et al., 2000a; Collins
et al., 2004). In development of novel excitation and detection techniques to over-
cometheseRFrelatedproblemselectromagneticandthermalmodellingtechniques
play a prominent role (Weiger et al., 2001; Katscher et al., 2004; Vaughan et al.,
2004; Van den Berg et al., 2006c).
This thesis addresses several electromagnetic and thermal aspects of regional hy-
perthermiaandMRimaging.Extensivedataacquistiontechniquesweredeveloped
to investigate the temperature heterogeneity of the prostate during regional hy-
perthermia treatment. Furthermore, a unique technique able to visualize RF field
patterns in MR imaging was employed to validate hyperthermia treatment plan-
ning. To facilitate a successful application of hyperthermia treatment planning in
the clinical practice, a new type of hybrid MRI/hyperthermia applicator is pro-
posed which cannot only provide image feedback on the anatomy, physiology and
temperature during treatment, but also on the electromagnetic field within the
patient.Suchadesignwillimprovequalityassurancetoanextentthatitbecomes
possible to profit from the merits of hyperthermia treatment planning and maxi-
mize target temperatures with planning based optimizations. In the final chapter
hyperthermiatreatmentplanningisappliedtoanalyzeRFfieldpatternsforwhole
body MR imaging at 3 Tesla. A method is presented which can reduce simultane-
ously RF field inhomogeneities and RF power deposition.