MRI Quantitative Analysis Of Liver Iron Overload

ObjectiveTo explore the accuracy and clinical value of the MRI quantitative diagnostic,which are liver / muscle signal intensity ratio and T2 values in vitro iron concentration and liver iron deposition. Materials and Methods1. Iron in vitro model of the MRI test: Iron model was maded with a 1.5L plastic bottle, containing 1.45L of distilled water as iron mold , placed together with an animal muscle specimens at the central, surrounding with sealed water bag contained about 2.5L of distilled water. After Each MRI scan of the iron model, injected 1ml of iron dextran with the iron content of 150mg/ml in the ferrous water mold and fully shaken, animal muscle specimens and sealed water bag remain unchanged. High concentrations of iron model: With a 1.5L plastic bottle filling with 1.30L water, did first scan after the injection of iron dextran 20ml, then before each scan injected with 10ml iron dextran, with a total of 200ml.Using GRE sequencing to measure ferrous water mold / muscle signal intensity ratio, using sequence of 8 echo and 4 echo to measure T2 value of ferrous water mold. Quantitative statistical analysis the relevance between the measured values of MRI and the concentration of ferrous iron water mode and then set up the linear regression equation.2. Quantitative MRI study of liver iron overload animal model: 20 adult male New Zealand white rabbits as the experimental group, with the weight of 2.0kg to 2.9kg. One same species rabbit as a normal control group. All rabbit weighed to calculate the dose of iron dextran injection. Deep intramuscular injected iron dextran for iron 150mg/ml with the dose of 15mg/kg weekly in the experimental group, alternate the injection position right to left hind leg. Injected a total of 15 weeks. Before the iron dextran injection ,MRI inspection was made to all rabbits, quantitative analysis of normal rabbit liver / muscle signal intensity ratio and T2 value of the liver. Every time one week after the injection of iron dextran to review the MRI,and the next day two rabbits were killed randomly to get the liver, after the measurement of liver volume, part of the liver,spleen and other organs were selected to pathological diagnosis and staging iron deposition, and the remaining liver tissue were dried for the measurement of LIC by atomic spectrophotometer. Rabbit of control group were killed after the first MRI examination, Excise the liver tissue for pathological examination and determination of LIC. All rabbits weighed again before the kill, and phlebotomized 2ml venous blood sample from marginal ear vein for the investigation of serum iron. MRI examination Sequences: GRE scan for liver / muscle signal intensity ratio, 8 and 4echo scan for the T2 value of the liver. Statistical analysis the relevance of hepatic iron content and the dose of the Injected iron dextran. Quantitative statistical analysis of MRI measured values and the LIC and set up the relevance of linear regression equation for the consideration of LIC in clinical trials,in accordance with the results of quantitative analysis of MRI calculation. 3. Clinical application of MRI quantitative research of the liver iron overload: 149 cases of thalassemia including 23 cases of thalassemia minor, 10 cases of thalassemia intermedia and 116 cases of thalassemia major.Thalassemia major group are divided into three groups according to different treatment methods: 23 cases for regular blood transfusions and chelation therapy with ICL670 (ICL670 group); 34 cases for regular blood transfusions and chelation therapy with Deferoxamine (DFO group); 59 cases for regular blood transfusions and no chelation therapy(no chelation group).Calculated liver iron concentration and liver iron content in accordance with the linear regression equation based on animal experiments. Six m onths later rechecked MRI in 57patients with thalassemia major, including 23 cases treated with ICL670, 34 cases treated with DFO. Evaluated the therapeutic efficacy of the two iron chelator taked into account of the total blood transfusions and the difference between the total liver iron within six months.Magnetic resonance imaging studies were performed using a 3.0 T Philips system (Achieva 3.0T X-series). Scan parameters: (1) Transverse GRE sequences for signal intensity ratio were acquired with TR of 48ms, TE of 2.5ms, flip angle of 60°, slice thickness of 10mm, gap of 3mm, scanning four slices, completed scan within one breath. (2) T2 value measurement with a multiple spin-echo (SE) pulse sequence: 8-echo axial scan for mild iron deposition were acquired with TR of 2000ms, TE of 8, 16, 24, 32, 40, 48, 56 and 64 ms, slice thickness of 7mm, scanning one slice , take time of about 8 minutes; 4-echo axial scan for severe iron deposition in the were acquired with TR of 2000ms, TE of 6, 12, 18 and 24 ms, slice thickness of 7mm, scanning one slice, take time of about 7 minutes. Results1. Iron in vitro model of the MRI test: The differences of the iron content of water mold / muscle signal intensity ratios and iron content of water mold R2 (1/T2) values measured by two radiologists for the first 15 scans are not statistically significant. The variation coefficient of the animal muscle specimens signal strength measured in GRE sequences was 6.08%; The variation coefficient of the animal muscle specimens signal strength measured in 8 and 4 echo sequences were 2.87% and 3.90% respectively. The T2 value of water is always 2047.00ms.With GRE sequences, there was apparent inverse linear relationship between iron concentration and the natural logarithm of model / muscle signal intensity ratio (r =-0.999, P = 0.000). With 8 echo SE sequences, R2 value of the water mold correlated closely with iron concentration (r = 0.998, P = 0.000) when the iron concentration is less than 1.74mg/ml. With 4 echo SE sequences, R2 value of the water mold correlated closely with iron concentration (r =1.000, P = 0.000) when the iron concentration is less than 2.64mg/ml.2. Quantitative MRI study of liver iron overload animal model: There was apparent linear relationship between LIC and the total iron injection (r = 0.824, P = 0.000). There was apparent linear relationship between total liver iron and total iron injection (r = 0.943, P = 0.000). Linear regression equation was seted up :? = 37.376 +0.505 X (?: total liver iron predicted based on the total dose of injected iron, X: the total dose of injected iron) (F = 153.993, P = 0.000). The average liver / muscle signal intensity ratio of the 21 rabbits measured by MRI before the injection is 1.43±0.13, and the average T2 value (measured in 8 echo sequence) is 55.35±6.23. The natural logarithm of liver / muscle signal intensity ratio measured by GRE sequence and LIC were significantly negatively correlated (r =-0.917, P = 0.000). Linear regression equation was set up: ?=5.640-5.044X (?: LIC predicted by MRI, X: the natural logarithm of liver / muscle signal intensity ratio measured by GRE sequence) (F = 100.895, P = 0.000). Liver R2 measured by 8 echo SE sequence and LIC values were significant linear correlation (r = 0.789, P = 0.000). Linear equation was set up: ? =- 2.93 +199.64 X (?: LIC predicted by MRI, X: T2 value of the liver measured by 8 echo sequence) (F = 31.403, P = 0.000). Liver R2 measured by 4 echo SE sequences and LIC values were significant linear correlation(r = 0.958, P = 0.000). Linear equation was set up: ? =- 2.76 +174.39 X (?: LIC predicted by MRI, X: T2 value of the liver measured by 4 echo sequence) (F = 213.154, P = 0.000).Pathological diagnosis and grading: the normal rabbit belonged to grade 0, 8 rabbits whose LIC was from 1.2 to 5.3mg/g belonged to gradeⅠ, and the 12 rabbits whose LIC was from 6.9 to 22.2mg/g belonged to gradeⅢ, There was no gradeⅡin the experiment.3. Clinical application of MRI quantitative research of the liver iron overload: (1) Independent-samples t test was used to determine the difference. There was no statistically significant difference of the liver / muscle signal intensity ratio between 20 normal adults and 21 normal rabbits (t =-1.416, P = 0.165); there was no statistically significant difference of the liver T2 values between 20 normal adults and 21 normal rabbits (t = 1.221, P = 0.232). (2) Liver T2 value of 4 echo sequence correspond to the clinical LIC diagnostic criteria can be calculated in accordance with the linear regression equation (equation 9): T2 value of liver more than 30ms indicates concerns forchelator toxicity; T2 value of liver of 17.5 to 30ms, optimal chelation range; T2 value of liver of 10 to 17.5ms, elevated hepatic iron levels; and T2 value of liver less than 10 ms, markedly increased iron levels and potential cardiotoxicity. (3) LIC of all the thalassemia minor and the normal group were within the normal range. Among the 10 cases of thalassemia intermedia: LIC was greater than 15mg / g in one case, from 7.0 mg / g to 15.0mg / g in 6 cases, less than 7.0 mg / g in one case and less than 1.6mg / g in 2 cases. Among the 116 cases of thalassemia major: LIC was greater than 15mg / g in 14 cases, from 7.0 mg / g to 15.0mg / g in 91 cases, from 3.2 mg / g to 7.0mg / g in 9 cases and less than 1.6mg / g in 2 cases who is less than 1-year-old. (4) Independent-samples t test was used to determine the difference. LIC of thalassemia minor is more than normal group;LIC of thalassemia minor is less than thalassemia intermedia; LIC of thalassemia intermedia is the same to thalassemia major. (5) Independent-samples t test was used to determine the difference. Total liver iron of thalassemia minor is more than normal group ;Total liver iron of thalassemia minor is less than thalassemia intermedia;Total liver iron of thalassemia intermedia is the same to thalassemia major. (6) Binary regression equation of the total liver iron , age and the volume of transfusion was set up : ? = 269.84 +429.65 X1 +3.29 X2 (?: total liver iron; X1: age; X2: the volume of transfusion ). (7) Among the thalassemia major with regular transfusions, by analysis of variance, there were significant differences in both liver iron concentration and liver iron content among the groups of no iron chelation therapy, chelation therapy with DFO, and chelation therapy with ICL670. Comparison liver iron concentration and liver iron content between the two groups, liver iron concentration and liver iron content of no iron chelation therapy group were more than groups of chelation therapy with DFO and chelation therapy with ICL670, liver iron concentration and liver iron content of chelation therapy with DFO were the same to chelation therapy with ICL670. (8)After six months of chelation therapy, the average amount of iron excretion was 3013.2±1684.5mg in DFO group,and 3179.5±1867.2mg in ICL670 group by random t test, the difference was not statistically significant (t =- 0.329, P = 0.743). (9) For the 23 cases of thalassaemia major receiving chelation therapy with ICL670 , LIC was decreased six months later, but there was no statistically significant difference of liver iron content before and after the therapy. (10) For the 29 cases of thalassaemia major receiving chelation therapy with DFO, LIC was Increased six months later, but there was no statistically significant difference of liver iron content before and after the therapy. Conclusion1. There were high repeatability, accuracy and stability of signal intensity ratio and R2 measurements on MRI.2. Both natural logarithm of liver / muscle signal intensity ratio and liver R2 values measured by MRI were significant correlated with LIC, the most significant line correlation was between liver R2 value measured by 4 echo SE sequence and LIC .3. The linear regression equation of both the natural logarithm of liver / muscle signal intensity ratio to LIC and liver R2 values to LIC set up through animal experiments applies to the human body. According to the equation,LIC of different types of thalassemia can be calculate based on liver / muscle signal intensity ratio or liver R2 value measured on MRI.4. LIC of thalassemia minor is in the normal range and needn't chelation therapy, but is more than the normal group; LIC of thalassemia intermediate and thalassemia major are higher, and need chelation therapy. quantitative analysis of MRI can provide the best time to receive chelation therapy.5. liver iron concentration and liver iron content of no iron chelation therapy group were more than groups of chelation therapy with DFO and chelation therapy with ICL670, liver iron concentration and liver iron content of chelation therapy with DFO were the same to chelation therapy with ICL670. There is no difference between the excretion iron respond to the two chelator in Six months...