2597 taken into account when adapting Gandon’s method on MR b1 > 400 s/mm2 increased contributions from restricted and systems of 3 T and up. All factors that influence T2* compartmentalised cellular environments tend to decrease (quality of the shim, inflammation, fibrosis, steatosis, etc.) ADC [25–27]. As a matter of fact, it has been shown that in will affect the quality of the measure and must be taken into the liver diffusion is not monoexponential [25, 28]. A recent account when interpreting the results. DWI study using ten b factors running from 0 to 800 s/mm2 In iron overload studies, more than 70% of body iron is indicated that the perfusion component is about 30%, found in the liver and liver iron content has been meaning that, unlike in the brain, the effects of perfusion are considered the best marker of total body iron burden far from negligible in the liver [28]. This has enhanced the [15]. However, hepatic iron deposition measured by MRI discrepancies between liver DWI studies from institutions and serum ferritin has shown little correlation with the iron using different b value sets, but also offers opportunities to levels in other organs, such as the pituitary gland or the study liver perfusion without the need for contrast injection. heart [15, 19]. Important decisions in, for example, the At this time, the latter prospect remains theoretical without clinical management related to cardiac risk, should there- any routine application in liver MRI up to now. The optimum fore not rely on these parameters [19]. b factors for the best contrast in imaging are related to TE, the signal-to-noise ratio of the sequence, the T2 and diffusion components of the studied structures. Diffusion In one clinical study, in which the b values were optimised for the detection and characterisation of benign and In the last decade, measurement of apparent diffusion malignant hepatic lesions, the specificities were similar for coefficient (ADC) of the water molecules through tissues all sequences [29]. However, the sensitivity for malignant has developed into another useful tool in the characterisa- lesions turned out to be highest for b1=100 s/mm2, whereas tion of hepatic lesions and in the evaluation of diffuse liver that for benign lesions was best for b1=800 s/mm2 [29]. At disease. This MRI application has no equivalent in other b1 values of 100 and, to a lesser extent, 200 s/mm2 the ADC diagnostic techniques. The principle is that in the presence values in hepatocellular carcinomas, metastases and hae- of magnetic field gradients, displacement of spins during mangiomas were elevated by perfusion contributions. This the echo time of a spin-echo sequence produces a phase compares with demonstrations that in normal liver and in shift of the transverse magnetisation. This loss of phase hepatocellular carcinoma at b=150 s/mm2 the contribution coherence in the transverse magnetisation causes a spin- to the capillary flow to the signal attenuation is eliminated echo amplitude attenuation in addition to that created by [30, 31] and that the mean perfusion fractions in liver, the spin-spin relaxation process [25]: hepatocellular carcinoma, metastasis and haemangioma are 0.29, 0.15, 0.22 and 0.35, respectively [30]. In another study, SðTEÞ ¼ Sð0Þ B expð TE=T2Þ (1) however, the ADC values in hepatocellular carcinoma, hepatic metastases, cavernous haemangioma and hepatic in which B is equal to exp(−b·D), with b a gradient factor cyst were found to be unaffected at b1 values of 100, 500 and depending on the gradient pulse sequence and D the 1,000 s/mm2, with decreasing spread of values at increasing diffusion coefficient. Diffusion-weighted imaging (DWI) b1, indicating that the calculated ADC values would be most was initially used for the qualitative assessment of the impact accurate at the highest b1 value used [32]. The ADC of of a gradient applied for a certain time per area unit on echo hepatocellular carcinoma is slightly lower than ADC in planar MR images. Right now, series measured with two or normal liver tissue, that of hepatic metastases was slightly more gradient factors are in use to be able to quantify ADC, higher and the ADCs of cavernous haemangioma and for example b=0 s/mm2 and b=1,000 s/mm2 (measured with hepatic cyst exceed the ADC of liver clearly [32, 33]. Here, it the same TE in order to eliminate the T2 term). In this case is noted that whereas the diffusion properties of simple cysts the ADC or the degree of molecular motion of water approximate those of free water, the ADC values of hydatid measured on DWI is calculated as follows: hepatic cysts, containing structures such as a visible cyst wall, multivesicular appearance, floating membranes or ADCb0;b1 ¼ b1 1b0 ln IIbb10 (2) tcnhaoelmcAiafi,DchaCetipovanati,lcuteemnsedotatfosmtbaseaelsisgl)ingtoahnttlhtyolelsoseiwooenfrsn[o(3hr4me]p.aaTltlohivceeecrllluounslaedrneecrlsaisrncoeisf- that the choice of b values is crucial in the detection of liver where Ib1 and Ib0 are the DW intensities measured using a tumours by DWI. This is illustrated by Fig. 3. The ADC high and low b value, respectively (for instance 0 and value of cirrhotic liver tissue is lower than that of normal liver 1,000 s/mm2). Studies on various organs in the human body and the ADC of liver in patients with haemosiderosis is very have shown that measured ADC values depend on the low [33]. Using b values up to 400 s/mm2, higher liver and gradient factors chosen, as at the lower end of the range cirrhotic liver ADC values were obtained than with b values (b1< 400 s/mm2) microcirculation or perfusion tends to of up to 800 s/mm2, whereas the significance of the increase the overall ADC value measured, whereas at difference between liver and cirrhotic liver was highest at