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MAGNETIC IRON DETECTOR (MID) WHOLE LIVER IRON OVERLOAD MEASUREMENT BY A NON CRYOGENIC PowerPoint PPT Presentation


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THALAS. Biomag 2006 - 15th International Conference on Biomagnetism August 20 - 26, 2006 Vancouver, BC, Canada. MAGNETIC IRON DETECTOR (MID) WHOLE LIVER IRON OVERLOAD MEASUREMENT BY A NON CRYOGENIC MAGNETIC SUSCEPTOMETER.

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MAGNETIC IRON DETECTOR (MID) WHOLE LIVER IRON OVERLOAD MEASUREMENT BY A NON CRYOGENIC

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Magnetic iron detector mid whole liver iron overload measurement by a non cryogenic

THALAS

Biomag 2006 - 15th International Conference on Biomagnetism

August 20 - 26, 2006 Vancouver, BC, Canada

MAGNETIC IRON DETECTOR (MID)

WHOLE LIVER IRON OVERLOAD MEASUREMENT BY A NON CRYOGENIC

MAGNETIC SUSCEPTOMETER

Mauro Marinelli1,2, Piergiorgio Beruto1, Barbara Gianesin1,2, Antonella Lavagetto3, Martina Lamagna3, Eraldo Oliveri2, Maria Luigia Saccone1, Giuliano Sobrero2, Laura Terenzani3, Gian Luca Forni3

1Physics Dept. University of Genova, Italy, 2National Institute of Nuclear Physics (INFN) Genova,3Centro della Microcitemia e Anemie Congenite, Ospedali Galliera, Genova, Italy


Magnetic iron detector mid whole liver iron overload measurement by a non cryogenic

Abstract

Assessment of body-iron accumulation is essential for managing therapy of iron-overload in diseases such as thalassemia, hereditary hemochromatosis and other forms of severe anemias. At present, the gold standard to determine liver-iron concentration (LIC) is the invasive liver needle biopsy; it might lead to large error, in assessing iron burden, due to the heterogeneous distribution of iron deposition in the liver. SQUID bio-susceptometer and MRI are currently the only non-invasive validated methods for LIC measurements.

The susceptometer presented herein measures directly the iron overload in the whole liver. All of its components operate at room temperature. Since February 2005 about 150 patients and 90 healthy volunteers have been measured. The result of correlations with the LIC measurements by SQUID susceptometry in 43 patients showed R = 0.86. In 2 patients, affected by Hemochromatosis, we correlated the LIC measurement by MID with the assessment of the expected iron depletion obtained with the phlebotomy therapy (R =0.94).

All the measurements were correlated with the serum-ferritin concentration values (R=0.72). We obtained correlation with the LIC measurement by liver biopsy in 7 patients (R = 0.89). The reproducibility of the iron overload of the same patients, measured after a relatively short lapse of time, is better than 0.5g.

The data obtained shows that MID is a reliable instrument for the diagnosis of the liver iron overload and for the follow-up of the chelation therapy. It is simpler to operate being manageable directly in the Clinical Center and more affordable than competing techniques.


Magnetic iron detector mid whole liver iron overload measurement by a non cryogenic

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Accurate assessment of body-iron accumulation is essential for managing therapy of iron-overload in diseases such as thalassemia, hereditary hemochromatosis and other forms of severe congenital or acquired anemias.

At present, the gold standard to determine liver-iron concentration (LIC) is the invasive liver needle biopsy; it might lead to large error in assessing iron burden due to the heterogeneous distribution of iron deposition in the liver.

E. Butensky et al., Am J Clinical Pathology 2005; 123; 146-152 "Although chemical analysis of liver biopsy samples is considered the gold standard for determining the Liver Iron Concentration ..concern has been raised that variability in the distribution of liver iron deposition exists and might lead to errors as high as 200% in assessing body iron burden by biopsy."

The distribution of the Liver Iron Concentration (LIC), obtained from the post-mortem examination of a thalassemic-patient liver, ranges from 10 (mg/g)* to 35 (mg/g)*

LIC (mg/g)*

* Dry weight


Magnetic iron detector mid whole liver iron overload measurement by a non cryogenic

Pickup

Magnet

The magnetic field flux, threaded with the pickup, is slightly modified by the diamagnetic (mainly from water) and paramagnetic (iron) properties of tissues.

It measures the iron overload in the whole liver


Magnetic iron detector mid whole liver iron overload measurement by a non cryogenic

Pickup

Magnet

Pickup

The symmetry, the mechanical stability and the accurate temperature control of the complete apparatusgivesthe sensitivity, better than 10-7, necessary to detect the iron quantity of interest.

All the susceptometer components operate at room temperature

Since February 2005, about 150 patients and 90 healthy

volunteers have been measured.


Magnetic iron detector mid whole liver iron overload measurement by a non cryogenic

Fiberglass

supporting

structure

Thermal shield

The signal of a smaller susceptometer, measuring rats, with and without the thermal shield.

without

with

Inside the accessible region he magnetic field is lower than 1.9 10-2 T (CEI EN 60601-2-3, 1997-02)


Magnetic iron detector mid whole liver iron overload measurement by a non cryogenic

x

rail

The stretcher moves on rails.

We average a few differences between the signals, with the stretcher in and out of the sensitivity region, to account for the changes of the environment magnetic properties.

This body position is to scan the liver region. Simply shifting the body allows measuring the magnetic signal of other body parts, for instance the head.


Magnetic iron detector mid whole liver iron overload measurement by a non cryogenic

Because of ~100 nV error, the minimum quantity of detectable iron inside the entire liver region of the phantom is ~130 mg of Fe3+ or ~270 mg of iron with an effective magnetic moment of 4 Bohr Magneton.

Small holes are evenly distributed on each of the phantom plastic slices.We poured paramagnetic powder, equivalent to 3g of Fe3+ and 15g of Fe3+, inside the holes placed in the phantom liver region.

The signal picked up by the susceptometer has two sources: an overall magnetic background of the torso and a possiblecontribution from liver iron excess.

After measuring the magnetic signature of a patient, statistical analysis methods and neural-network simulations (trained using the control data) are employed to estimate the background signal given the patient anthropometric data. Liver-iron overload is then determined by subtraction of the estimated background from the total measured signal.


Magnetic iron detector mid whole liver iron overload measurement by a non cryogenic

The signal of a patient, with 12.4±1 g of iron overload in the liver, is compared with the one of a healthy volunteer, having close anthropometric data.

The abscissa x (cm) is the position of the center of the human body relative to the magnetic field axis.


Magnetic iron detector mid whole liver iron overload measurement by a non cryogenic

y

Magnetization signal

x

Eddy Current signal

Magnetic flux from the

body magnetization

Magnetic flux from the

body eddy currents

EDDY CURRENT SIGNAL

Because of the inductance of the eddy currents loops within the human body and the tissue resistivity, the delay of the eddy currents relative to the induced electric field isnegligible.


Magnetic iron detector mid whole liver iron overload measurement by a non cryogenic

THE EDDY CURRENT SIGNAL DOES NOT DEPEND ON THE IRON

  • J. F. Schenck, E. A. Zimmerman, “Review Article High-field magnetic resonance imaging of brain iron: birth of a biomarker?,”N.M.R. Biomed, no. 17, pp. 433-445, 2004 “The concentration of iron in the tissues as free aqua ions is not significant”

  • In all the patient measurements we never noticed the iron overload skewness on the eddy current signal.

The eddy current signal of the patient P029 is almost the same before and after the removal of his spleen, containing a large amount of iron.

The eddy current signal of the patient P108, with more than 12g of liver iron overload, does not show any skewness


Magnetic iron detector mid whole liver iron overload measurement by a non cryogenic

x

0

Both the eddy current and magnetization signals of a person without iron overload have a similar dependence on the body size.

The estimation of the signal of the patient, supposed depleted by the iron overload (background signal), is based on his eddy current signal and anthropometric data.


Magnetic iron detector mid whole liver iron overload measurement by a non cryogenic

Spleen: 14 slices

mgFe/gdw

9.1

22.5

3.1

6.8

24.7

3.2

18.6

6.6

1.0

1.5

4.2

1.3

1.3

7.6

According with the chemical analysis of the cut off spleen (1350 g), the held iron was about 2.7g.

Liver biopsy

No iron overload

in the liver

The expected magnetization signal, obtained before the splenectomy, using the eddy current signal and the other patient's anthropometric data.


Magnetic iron detector mid whole liver iron overload measurement by a non cryogenic

P 003

P 068

Measured (a) andBackground (b) signals of two patients affected by Congenital Hemocromatosis.

The iron depletion is obtained with the phlebotomy therapy.


Magnetic iron detector mid whole liver iron overload measurement by a non cryogenic

The iron reduction, measured by MID, is comparedwith the assessment of the iron depletion obtained with the phlebotomy therapy

The iron overload measurements of the two Hemochromatosis patients


Magnetic iron detector mid whole liver iron overload measurement by a non cryogenic

Measured (a) andBackground (b) signals of a Thalassemia Major patient, treated with 40mg/Kg of DFO 4 days per week and 75mg/Kg of Deferipron 7 days a week.


Magnetic iron detector mid whole liver iron overload measurement by a non cryogenic

The MID sensitivity is about 1g (1SD).

It depends on the model to calculate the background signal.

The reproducibility of the iron overload of the same patients, measured after a relatively short lapse of time, is better than 0.5 g


Magnetic iron detector mid whole liver iron overload measurement by a non cryogenic

Liver volume = (25cc/Kg) x (Patient’s body weight)

(Ratio between dry-weight and wet-weight iron concentrations) = 5.83

The Liver Iron Concentration (LIC) of 7 patients from the MID and the Biopsy of their liver

The LIC, measured by MID, is compared with the LIC measured by SQUID (Dr. A. Piga, Turin, Italy)on the same patients


Magnetic iron detector mid whole liver iron overload measurement by a non cryogenic

The blood serum-ferritin reduction, of the two hemochromatosis patients, is compared with the reduction of the liver iron, measured by MID.


Magnetic iron detector mid whole liver iron overload measurement by a non cryogenic

Comparison of the blood serum-ferritin variation with the measured variation of the iron in the liver of 27 patients, that have been measured at least twice by MID.

MID Liver Iron Overload

vs

Blood Serum-ferritin Concentration


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