Inductive heating of ferrimagnetic particles and magnetic fluids: Physical evaluation of their potential for hyperthermia

Figures & data

Table I.  Multidomain ferrite particles (MDP) and soft iron powder (no. Fe) used for power absorption measurement in an AC magnetic field. Particle size distribution and surface structure determined by light microscopy.

MDP ferrite no.	Milling	Commercial	Elements	Shape	Size distribution (µm)	Surface	Manufacturer
360G	Yes	Yes	Ni–Zn–Fe-0	Irregular	10–100	Rough	Vogt Electronic
60	No	Yes	Ba–Co–Fe–O	Irregular	100–300	Rough	S + M Components
TK-T4	No	No	Ni–Zn–Fe–O	Spherical	1–100	Smooth	BASF
322	No	Yes	Ni–Zn–Fe–O	Spherical	200–400	Smooth	Vogt Electronic
360	No	Yes	Ni–Zn–Fe–O	Spherical	200–400	Smooth	Vogt Electronic
221G	Yes	Yes	Ni–Zn–Fe–O	Irregular	10–100	Rough	Vogt Electronic
TK-T2	No	No	Ni–Zn–Fe–O	Ellipsoid	1–100	Smooth	BASF
Fe	No	Yes	Fe	Irregular	1–100	Rough	Emerson & Cuming
23	No	No	Ni–Zn–Fe–O	Irregular	1–100	Rough	BASF
1680	No	No	Mn–Zn–Fe–O	Rodshape	0.8–10	Smooth	BASF
KG-T4	No	No	Ni–Zn–Fe–O	Irregular	10–100	Rough	BASF
KG-T2	No	No	Ni–Zn–Fe–O	Spherical	1–100	Smooth	BASF
10 000	No	No	Mn–Zn–Fe–O	Irregular	40–150	Rough	Kaschke

BASF: BASF AG, 6700 Ludwigshafen, Carl-Bosch-Str. 38, Germany.

Emerson & Cuming: Emerson & Cuming Europe, Distr.: EMC-Technik u. Consulting GmbH, 7000 Stuttgart 80, Schultze Delitzsch-Str. 58, Germany.

Kaschke KG: Kaschke KG GmbH & Co., 3400 Göttingen, Rudolf-Winkel-Str. 6, Germany.

S + M Components: Siemens Matsushita Components GmbH & Co. KG, 8000 München 80, Germany.

Schering: Schering AG, 1000 Berlin 65, Müllerstr. 170–178, Germany.

Vogt Electronic: Vogt Electronic AG, 8391 Erlau bei Passau, Postfach, Germany.

Figure 1. Experimental set-up for SAR measurements with applicator device 2 for frequencies from 0.3 to 5 MHz. When using the shorter coil of applicator device 1, liquid column (sample volume) was reduced to prevent thermal gradients induced by magnetic field inhomogeneities near the edges of the coil. Surface cooling effects were low because of the effective Styrofoam insulation around the sample tube.

Table II.  Subdomain ferrite particles suspensions (SDP) used for power absorption measurement in an AC magnetic field. Core sizes determined by transmission electron microscopy (Siemens EM 102). Both types of SDP are of spherical shape.

SD ferrite no.	Dispersion medium	Suspension	Core elements	Commercial	Average core size (nm)	Manufacturer
65IIB	Dextran 4000	Poorly stabilized	Mn–Zn–Fe–O	No	7.6 ± 1.8	BASF†
P6	mod. dextran	Stabilized	Fe–O	No	3.1 ± 0.7	Schering†

†See note for Table I.

Figure 2. SAR of multidomain ferrite particles (MDP) embedded in 2% agar matrix (in 4.7 g/l NaCl). Magnetic field strength ∼13.2 kA/m, frequency 520 kHz.

Figure 3. SAR of multidomain ferrite (MDP) no. KG-T4 compared with subdomain ferrite (SDP) no. P6 (coated) as a function of AC magnetic field strength. Frequency: 520 kHz. Particles embedded in 2% w/v agar matrix (in 4.7 g/l NaCl) and 100 mg/ml dextran solution, respectively. The solid lines are the result of a third-order polynomial regression fit.

Figure 4. SAR of subdomain poorly stabilized ferrite no. 65IIB compared with coated subdomain ferrite no. P6 as a function of AC magnetic field frequency (1–5 MHz), normalized for 500 A/m magnetic field strength. The solid lines are the result of a linear regression fit.

Figure 5. SAR of subdomain poorly stabilized ferrite no. 65IIB and coated subdomain ferrite no. P6 as 1 : 10 dilution in distilled water or glycerol as a function of AC magnetic field frequency (10–80 MHz), normalized for 500 A/m magnetic field strength (§ 2.1). The solid lines are the result of a second-order polynomial regression fit.

Figure 6. SAR of subdomain coated ferrite no. P6 (suspended in 10% (w/v) dextran heated by an AC magnetic field (strength ∼11.3 kA/m, frequency 520 kHz) in dependence on static magnetic field strength H_stat perpendicular to the AC field z-axis. The solid line is the result of a fourth-order polynomial regression fit.

Figure 7. Expected power absorption (based on experimental heating data, § 3.2) of 5 mg ferrite no. P6 per ml tumour volume with an inductive tissue load (muscle-equivalent, σ_T = 0.4 Ω⁻¹ m⁻¹) of 25 mW/ml at max. radius r = 15 cm as a function of AC magnetic field frequency and magnetic field strength.

Figure 8. Expected power absorption (based on experimental heating data, § 3.2) of 1 mg ferrite no. P6 per ml tumour volume with an inductive tissue load (muscle-equivalent, σ_T = 0.4 Ω⁻¹ m⁻¹) of 25 mW/ml at max. radius r = 10 cm as a function of AC magnetic field frequency and magnetic field strength.