Quantitative evaluation of diffusion-weighted magnetic resonance imaging of focal hepatic lesions

Abstract

AIM: To explore the quantitative analysis of diffusion-weighted magnetic resonance imaging (DWMRI) in differential diagnosis of focal hepatic lesions.

METHODS: DWMRI was performed in 149 hepatic lesions, including hepatocellular carcinoma (34 cases), hepatic metastases (37 cases), cavernous hemangioma (42 cases), hepatic cyst (36 cases). Apparent diffusion coefficient (ADC) values were evaluated using four different b values in different sequences. The ratio of ADC values of lesion/liver in hepatocellular carcinoma and hepatic metastases was also calculated.

RESULTS: The mean ADC values of hepatic lesions were as follows: hepatocellular carcinoma (0.95 ± 0.11)×10^-3 mm²/s, hepatic metastasis (1.13 ± 0.21)×10^-3 mm²/s, cavernous hemangioma (1.86 ± 0.36)×10^-3 mm²/s, hepatic cyst (3.14 ± 0.31)×10^-3 mm²/s. The ratio of ADC values in lesion/liver in hepatocellular carcinoma was 0.91± 0.11, being significantly different from that in hepatic metastasis (1.21 ± 0.18, P < 0.05).

CONCLUSION: ADC values and quantitative analysis of focal hepatic lesions are of significant values in differential diagnosis of focal hepatic lesions.

Key Words: Diffusion-weighed magnetic resonance imaging, Hepatic lesion, Quantitative analysis

INTRODUCTION

Diffusion-weighted magnetic resonance imaging (DWMRI) is a new technique of magnetic resonance imaging (MRI) at the level of molecular movements and can reflect the functions and structures of the body without trauma. It has been used to diagnose diseases in the central nervous system[1-3]. Radiologists have paid more attention to its values in differential diagnosis of focal hepatic lesions[4-6].

This study was to evaluate the value of DWMRI in differential diagnosis of focal hepatic lesions by quantifying apparent diffusion coefficient (ADC) values.

MATERIALS AND METHODS

In this study, DWMRI was performed in 149 patients with focal hepatic lesions (31 women and 109 men, aged 24-89 years, mean 52.37 years), including 34 hepatocellular carcinomas, 37 hepatic metastases, 42 cavernous hemangiomas, 36 hepatic cysts. The diameter of the above lesions was 1.1-20.5, 0.8-25.8, 0.9-8.6, and 0.8-2.7 cm, respectively.

The criteria for selecting the patients were as follows: (1) The diagnosis of all cases of hepatocellular carcinoma was confirmed by α-fetal protein, clinical data, ultrasound, CT or/and MR imaging, and pathology. (2) All cases of hepatic metastasis of primary malignant tumors were surgically confirmed. (3) The diagnosis of all the cases of cavernous hemangioma and hepatic cyst was confirmed by clinical data, ultrasound, CT or/and MR imaging, and follow-up observation.

DWMRI was performed by 1.5 T MR scanner with a body coil (Signa, Horizon LX, GE, USA). All data were measured in control console. All lesions were scanned with spin-echo (SE) T1WI and fast SE T2WI in the axial plane. The imaging parameters of DWMRI with SE-echo planar imaging (EPI) sequence were set as follows: repetition time ms/echo time ms: 10 000/90; matrix: 128×128; field of view: 36 cm×36 cm; section thickness: 8 mm; gap: 2 mm; slice number: 10-15; one signal. Four different b values (b=0 mm²/s, 100, 500, 1 000 mm²/s) and three directions were used, total acquisition time was 40 s.

The standards of measurement of signal intensities in hepatic lesions on DWMRI were as follows: the largest diameter of lesions was measured, three regions of interest in each lesion were marked off and measured, the regions of blood vessels and artifacts were rejected, the edges of parenchyma in the lesion were measured, when apparent necrosis was present, and regions of interest should involve parenchyma and the diameter of it should be longer than 1 cm, the same area of the section should be chosen for the measurement of different sequences, the signal intensity of each ROI was measured thrice and a mean value of SI was acquired for ADC calculation.

ADC values were evaluated with the following formula: ADC=(ln[S_l+S_h])/(b_h-b_l), where ln is the natural logarithm, S_l and S_h are the signal intensities of low b value and high b value, respectively.

All data were expressed as mean±SD. Statistical analysis was performed by t-test using SPSS software 10.0. P<0.05 was considered statistically significant.

RESULTS

In this study, 149 focal hepatic lesions were detected by DWMRI, the DWMRI sensitivity was 100%. We used four different b values (b = 0, 100, 500, and 1 000 mm²/s). The higher the b values on the DWMRI (b = 1 000 mm²/s). The lower the b values on DWMRI (b = 100 mm²/s), the higher the ADC values. Thus, we measured the highest b value (b = 1 000 mm²/s) on DWMRI. Table 1 shows the ADC values in focal hepatic lesions.

Table 1 ADC values in focal hepatic lesions (×10^–3 mm²/s).

Hepatic lesion	b = 100	b = 500	b = 1 000
Hepatocellular carcinoma	0.56-1.33	0.60-1.31	0.57-1.23
Hepatic metastases	0.75-1.62	0.71-1.59	0.72-1.35
Cavernous hemangioma	1.26-2.54	1.32-2.36	1.37-2.21
Hepatic cyst	2.70-3.85	2.73-3.71	2.78-3.51

The ADC values in hepatic cyst were significantly higher than those in hepatic hemangioma, metastasis, and hepatocellular carcinoma, respectively; the t-test value was 2.329-3.237 (P < 0.01). There was a significant difference in ADC values of hepatic hemangioma, hepatic metastasis, and hepatocellular carcinoma, respectively, with the t-test value being 1.139-3.467 (P < 0.05). No significant difference was demonstrated between hepatic metastasis and hepatocellular carcinoma with the t-test value being 1.432 (Table 2).

Table 2 ADC value in focal hepatic lesions (b = 1 000 mm²/s, mean±SD).

Hepatic lesion	ADC value (×10-3 mm2/s)
Hepatocellular carcinoma	0.95 ± 0.11
Hepatic metastases	1.13 ± 0.21
Cavernous hemangioma	1.86 ± 0.36
Hepatic cyst	3.14 ± 0.31

The ratio of ADC values of lesion/liver between hepatocellular carcinoma and hepatic metastasis was significantly different with the t-test value being 2.328 (Table 3).

Table 3 Ratio of ADC values of lesion/liver between hepatocellular carcinoma and hepatic metastasis (mean ± SD).

Hepatic lesion	Coverage	Ratio of ADC values of lesion/liver
Hepatocellular carcinoma	0.73-1.05	0.91 ± 0.11
Hepatic metastases	1.07-1.43	1.21 ± 0.18

DISCUSSION

Diffusion is known as the Brownian motion caused by thermal movement of molecules, and is arbitrary and irregular. The effect of molecular diffusion movement is weak, but it can result in MR signal missing converge, the attenuation degree lies on MR gradient intensity and amplitude of molecular movement[7,8]. DWMRI is an imaging method to observe microcosmic molecular movement using macroscopical flowing phase displacement theory. Body diffusion coefficient is affected by microcirculation factors[9], such as humoral flowing, cellular osmosis and temperature, perfusion of capillary vessels, glutinous degree and proportion of intra- and extra-cellular water, direction of cellular membrane transition. It is also affected simultaneously by macro factors and circadian function, such as breath, pulsate, and peristalsis. In fact, apparent diffusion coefficient (ADC) regularly replaces the diffusion coefficient, and is always greater than the latter[10,11].

In theory, ADC value can be obtained by one pulsate sequence using two different b values. In experimental researches and clinical applications, ADC values are constantly related to the kinds and quantities of b value in sequences and perfusion of tissue[12-14]. The bigger the b value, the more accurately the ADC value. We measured the four different b values in different sequences (b=0, 100, 500, and 1 000 mm²/s), and found that ADC values had higher stabilization with higher b values. The technique of EPI, which has a more rapid imaging speed and higher section efficiency, could complete signal collection of single images in several milliseconds and freeze-up artifact of physiological functions. Therefore, it is the commonly used diffusion imaging sequence[15-17]. We adopted images of 1 000 mm²/s as a reference to give enough attention to attenuation degrees of four different lesions.

Animal experiments and clinical researches indicate that ADC value depends on imaging materials and molecular spatial distribution[18,19]. Cavernous hemangioma and hepatic cyst are mainly composed of liquid component, which has more movement freedom in the two lesions; ADC values are greater than those in hepatic parenchymatous mass. Cavernous hemangioma often presents fiber septation, scar, and hemorrhage, and the blood glutinous degree is higher than that of hydatid fluid in hepatic cyst. This is why the ADC value in hepatic cyst is lower than that in cavernous hemangioma[20-22]. Thus, entity mass, cavernous hemangioma and hepatic cyst have significantly different ADC values. These findings are consistent with the results in our study.

Our results indicate that the different ADC values in DWMRI could differentiate hepatic cyst and cavernous hemangioma from other hepatic entity masses[23]. We also analyzed the ratio of ADC values of the lesion/liver. Statistical analysis demonstrated that ADC ratio was different between hepatocellular carcinoma and hepatic metastasis.

We believe that the ratio of ADC value of lesion/liver could differentiate hepatocellular carcinoma from hepatic metastasis, and provide some information for the diagnosis of focal hepatic lesions that are less than 3 cm in diameter. This theory is based on the situation in our country that hepatocellular carcinoma generally results from cirrhosis, but hepatic metastasis is not the case[24-26]. Although the ADC values in hepatic metastasis foci are slightly greater than those in hepatocellular carcinoma foci, the ADC values in liver parenchyma with hepatic metastasis are lower than those in hepatocellular carcinoma. Patients with hepatic metastasis have a higher ratio of ADC values of lesion/liver than those with hepatocellular carcinoma.

In conclusion, DWMRI is a new functional MRI technique, and is of great value in the differential diagnosis of focal hepatic lesions.