| Part 1.Application of 3.0T Diffusion-weighted MR Imaging in Focal Liver LesionObjective:Powered by tremendous advances in technology and image quality over the past few years, DW imaging has drawn strong interest from the radiologic community and major MR vendors. DW imaging is increasingly used in the abdomen, particularly in the liver, with promising results for FLL detection, characterization and diagnosis. DWI was appreciated in differentiation of FLLs for its indirect reflecting cell microstructures and function. ADC provides quantitative characterization of liver lesions and helps discrimination between benign and malignant focal liver lesions. In general, benign FLLs have higher ADC values than malignant FLLs, but there are also variable degrees of overlap between them. Several cutoff ADC values (1.40-1.65×10-3mm2/sec) have been suggested in the literature for differentiating malignant from benign FLLs, with reported sensitivity of 74% to 100% and specificity of 77% to 100%.Despite widespread clinical use of such an advanced MRI technique, DWI in the abdomen is still known to be highly sensitive to organ motions. Several studies reported that cardiac motion has an impact on DWI of abdomen, resulting in higher ADC of normal liver parenchyma in left compared with right hepatic lobes.In addition, Schmid-Tannwald et al. reported that ADC of benign and malignant FLLs calculated from noncardiac-gated DWI were significantly higher in the left hepatic lobe. Therefore, variations of ADC of FLLs caused by their locations in the liver may indicate an important limitation of DWI, and potentially impact effectiveness for characterizing FLLs. However, by dividing the liver into left and right hepatic lobes instead of regarding it as a whole, the ADC cutoffs for FLLs may be different. In addition, the diagnostic accuracy for lesion discrimination using different ADC cutoffs in left hepatic lobe, right hepatic lobe and whole liver may also be different. However, such studies are limited.The first purpose of the present study was to measure and compare ADCs of normal liver parenchyma and FLLs in left hepatic lobe and right hepatic lobe, and to determine whether ADCs of normal liver parenchyma and FLLs, calculated from noncardiac-gated DWI acquisitions, are different in left hepatic lobe and right hepatic lobe. The second purpose of this study is to characterize focal liver lesions in each hepatic lobe, and to differentiate malignant lesions from benign lesions using different ADC cutoffs in left hepatic lobe, right hepatic lobe and whole liver.Methods:Through a retrospective search in the radiology patient database,356 consecutive patients with FLLs (excluding hepatic cysts) underwent abdominal magnetic resonance examination of the liver between October 2010 and March 2013. Eighty-seven patients were excluded from our analysis under exclusion criteria:i) FLLs with the diameter< 1 cm were present, ii) sufficient confirmation of the nature of the lesions was not available, iii) distinct artifacts were observed on DWI, and iv) chemotherapy and radiofrequency ablation had been performed within the last 12 months prior to the magnetic resonance examination. Hence, our retrospective analysis included 269 patients (180 males,89 females, age range of 21-80 years and mean age 54.7 years). In patients with the number of lesions≥5 for each lesion type, five lesions were randomly selected for quantitative measurements by the study coordinator. Thus, a total of 429 hepatic lesions were included.Fifty-eight patients who were selected from all 269 patients were studied as Group A (37 males and 21 females, with a mean age of 54.4 years). The inclusion criteria were:ⅰ) the patient at least had two FLLs, one in left hepatic lobe and the other in right hepatic lobe; ⅱ) the two lesions in left hepatic lobe and right hepatic lobe, respectively, in each patient were of the same etiology and similar MRI features; and ⅲ) the two lesions in each patient had similar sizes. Patients whose FLLs possessed large regions of necrosis and cystic degeneration were excluded. All 269 patients were investigated as Group B.All patients were examined on a 3.0-T MRI system (Magnetom Verio, Siemens, Germany). For full evaluation of the FLLs, breathhold transverse T2-weighted fast spin-echo sequences were initially performed, followed by transverse T1-weighted dual-echo in-phase and out-ofphase sequences. Three-dimensional fat-saturatedT1-weighted dynamic contrast-enhanced sequence (volume interpolated body examination, Siemens, Germany) was given during suspended respiration. Gadobenate dimeglumine (Gd-BOPTA, MultiHance; O.lmmol/kg) was injected intravenously at a rate of 2.5 ml/s by a power injector, followed by a 20-mL saline flush.Before dynamic contrast-enhanced imaging, transverse respiratory triggered DW SS-EPI sequence was performed by using two b values of 0 and 800s/mm2. ADC maps were generated with a commercially available software workstation system (Syngo Multimodality workplace, Siemens, Germany) base on ADC=-ln(S (b=800)/S (b=0))/800. The technical parameters were as follows:TR,4000 ms; TE,73 ms; echo train length,92; receiver bandwidth,2442 Hz/pixel; number of signal averages,3; section thickness,5 mm; intersection gap,1 mm; 30-35 transverse sections acquired; acquisition time,4-6 min.The study coordinators recorded the final diagnoses of all selected lesions and their location, and drawn the ROI on the ADC map. ROIs of normal liver parenchyma were drawn as large as possible without involving intrahepatic vessels and this procedure was performed carefully to exclude motion artifacts. ROIs of FLLs were placed within the solid part of lesions as large as possible, avoiding necrosis and cystic degeneration. The mean ADC value of a lesion was calculated by averaged the ADC values of all voxels in all ROIs of a lesion. A lesion contained more than one ROI when the lesion was bigger. Mean where, n was the number of ROIs for a lesion; ADC, was the mean ADC of the ith ROI; S, was the area of the ith ROI. Because the areas of ROIs in a lesion often differed greatly, the area Si was as the weight of the ADCi; the equation can calculate the mean ADC accurately.FLLs were diagnosed and characterized on the basis of consensus review by two radiologists of the MRIs, clinical history, pathologicfindings, follow-up imaging results.In Group A, sizes of FLLs in left hepatic lobe and right hepatic lobe were compared using paired t-test. ADCs of normal liver parenchyma and benign and malignant FLLs between the left hepatic lobe and right hepatic lobe were compared using paired t-test. In Group B, the mean ADCs of CCC, HCC and metastases were compared using Analysis of Variance. The mean ADCs of hemangioma and FNH were compared using independent-sample t-test. The mean ADCs between benign and malignant FLLs were compared using independent-sample t-test in left hepatic lobe and in right hepatic lobe. ROC curve analysis was used to test the ability of ADCs in differentiating malignant from benign FLLs in left hepatic lobe, right hepatic lobe and whole liver. The AUC was calculated and compared between left hepatic lobe and whole liver, as well as right hepatic lobe and whole liver. The optimal ADC cutoffs in left hepatic lobe, right hepatic lobe and whole liver were determined by ROC analysis and Youden index and p< 0.05 was considered to have statistically significant difference. All statistical analyses were performed using SPSS version 17.0 for Windows.Results:For all patients with CCC,58 patients with HCC and 33 patients with metastases, histopathologic verification of the lesions by means of biopsy and/or surgery was available. The diagnosis of the remaining HCC and metastases was established on the basis of typical MRI findings, clinical history, pathologic tracer uptake of the lesions by positron emission tomography-computed tomography, and follow-up imaging studies. There were a total of 125 cases of benign lesions, including 9 cases of FNH and 116 cases of hemangiomas. Histopathologic verification was available in 5 cases of FNH and 5 cases of hemangiomas. The remaining cases of benign lesions showed typical MRI findings in conjunction with stability in lesion size and morphology on serial cross-sectional imaging studies with a minimal follow-up interval of 6 months.In Group A, the average ROI size of normal liver parenchyma was similar in the left and right lobe of the liver (756.04±462.48 mm2 vs 982.28±589.24 mm2; P= 0.358). The mean ADC value of normal liver parenchymawas significantly higher (P =0.000) in the left hepatic lobe (1.69±0.21×10-3mm2/sec) than in the right hepaticlobe (1.35±0.17×10-3mm2/sec). The average ROI size of benign and malignant FLLs was similar in the left and right lobe of the liver (3.15±1.72 cm vs 3.35±1.77 cm; P=0.236). The mean ADC value of benign FLLs was significantly higher in the left hepatic lobe (2.38±0.62×10-3mm2/sec) than in the right hepatic lobe (1.88±0.57×10-3mm2/sec; P=0.006). The mean ADC value of malignant FLLs was also significantly higher in the left hepatic lobe (1.21±0.25×10-3mm2/sec) than in the right hepaticlobe (0.98±0.20×10-3mm2/sec; P=0.000). In addition, the mean ADC value of benign FLLs was significantly higher than that of malignant FLLs in both the left (2.38±0.62×10-3mm2/sec vs.1.21±0.25×10-3mm2/sec, respectively; P= 0.000) and right hepatic lobes (1.88±0.57×10-3mm2/sec vs.0.98±0.20×10-3mm2/sec, respectively; P= 0.000).In Group B,179 (42%) of the 429 FLLs were located in left lobe and the remaining 250 (58%) were located in right lobe. ADC values of metastases overlapped strongly with those of HCC and CCC in the both lobes, but the difference did not reach statistical significance (p>0.05 for all). ADC values of hemangiomas overlapped strongly with that of FNH, the difference did not reach statistical significance (p> 0.05) in the left lobe, but a statistically significant difference was observed between them (p<0.05) in the right lobe. Although CCC showed a slightly lower mean ADC compared with that of HCC and metastases in the both lobes, a statistically significant difference was not observed between them (p> 0.05 for all). Compared with hemangiomas, FNHs showed a slightly lower mean ADC, but the difference did not reach statistical significance (p=0.236) in the left lobe, but a statistically significant difference was observed between them, (p=0.014) in the right lobe.In Group B, the mean ADC of benign FLLs was significantly higher (p<0.001 for all) than that of malignant ones in left hepatic lobe (2.34±0.72×10-3mm2/sec vs 1.12±0.27×10-3mm2/sec), right hepatic lobe (1.82±0.51×10-3mm2/sec vs 0.96± 0.21×10-3mm2/sec) and whole liver (2.05±0.66×10-3mm2/sec vs 1.02±0.25× 10"3mm2/sec). ROC curve analysis showed that ADCs obtained with b values of 0 and 800 second/mm2 were highly predictive for distinguishing malignant from benign focal liver lesions in left hepatic lobe, right hepatic lobe and whole liver, with the AUC being 0.977,0.990 and 0.976. For distinguishing malignant lesions from benign lesions, the sensitivity and specificity were 90.4% and 94.7% when cutoff (mm2/sec) was 1.41×10-3in whole liver,92.6% and 92.0% when cutoff was 1.46×10-3 in left hepatic lobe, and 94.4% and 94.4% when cutoff was 1.25×10-3 in right hepatic lobe. The AUC of right hepatic lobe was higher than the AUC of whole liver (p< 0.05), but there was no significant difference between the AUC for left hepatic lobe and whole liver (p>0.5). The accuracy of optimal ADC cutoffs for distinguishing malignant lesions from benign lesions in left hepatic lobe, right hepatic lobe and whole liver was 97.7%,99% and 97.6%. These data indicated that malignant lesions and benign lesions can be distinguished in left hepatic lobe, right hepatic lobe and whole liver by analyzing the ADCs using ROC curves.Conclusion:ADCs of normal liver parenchyma and benign and malignant FLLs in left hepatic lobe calculated from noncardiac-gated DWI acquisitions were significantly higher compared with those in right hepatic lobe. ADCs in DWimaging with b values of 0 and 800s/mm2 were highly predictive for distinguishing malignant FLLs from benign FLLs. When dividing the liver into left hepatic lobe and right hepatic lobe instead of regarding the liver as a whole, optimal ADC cutoff for FLLs in right hepatic lobe can achieve higher diagnostic accuracy compared with that in whole liver, but this was not the case in left hepatic lobe. This finding may help improve the diagnosis of the focal liver lesions in right hepatic lobe.Part 2. Application of three-dimensional magnetic resonance volumetry in the pituitary gland of short stature childrenObjectives:GHD is associated with a marked variety of neuroanatomical abnormalities, including a hypoplastic pituitary gland, as identified by MRI. Neuroimaging has become an essential part of the diagnostic process for children with GHD in measuring gland size due to the excellent contrast and high spatial resolution. Currently, the majority of pituitary gland measurements are focused on height, which is considered to be the standardindicator for pituitarygland size. However, the size and shape of the normal pituitary gland vary considerably and are also affected by age, gender and the hormonal environment. The variation in shape of the pituitary gland between individuals means that any assessment of size is likely to be subject to a high degree of imprecision unless a true volume is measured.Previously, studies directly measured and indirectly calculated pituitary gland volumes using 3D volumetry and 2D thin-slice MRI, respectively, for more precise assessments. Fink et al recommended that one-dimensional (height) and indirect (2D) estimations of pituitary gland size and volume should be replaced by direct volumetric analysis. However, only a few studies have focused on adolescents or children with short stature.The aim of the present study was to obtain standard reference values for the pituitary gland volumes of healthy children and to analyze the potential diagnostic values of pituitary gland volumetry for GHD and ISS.Methods:A group of 75 healthy children aged between 1 and 19 years were recruited to obtain normal volumetry values of the pituitary gland. These individuals demonstrated no evidence of abnormalities to the central nervous or endocrine systems prior to the study. An additional group of 55 children with GHD (n=32) or ISS (n=23) aged between 0 and 14 years were included in the measurement of pituitary gland volume and height. The volume of the pituitary gland was measured using a thin-section 3D MRI sequence of magnetization-prepared rapid gradient echo imagingwith a section thickness of 1 mm. The following parameters were used:TR, 1900 ms; TE,2.45 ms; excitation,1; section thickness,1 mm; inversion time,900 msec; flip angle,9°; field of view,250 mm; and matrix,256×246. The total imaging time was 4 min 18 sec.MRI scans were processed with a commercially available software workstation system (Syngo Multimodality workplace, Siemens, Germany). In all the cases, the volume was measured on the sagittal imageas the boundary is simple to define in this orientation. The ROI were determined layer-by-layer with manual tracing using a mouse-guided cursor. The regions did not include the pituitary stalk, but included the neurohypophysis.The volume of the pituitary gland was then calculated using the section thickness and the ROI of every layer. The midsagittal height was obtained from the straight-line distance fromthe adenohypophysis midpointof the upper edgeto the edge of the gland in the sella turcica bottom, according to the traditional method described by Fujisawa. A comparison was performed between the short stature children and normal children. Pituitary gland volumes below the minimum value of the corresponding normal range were regarded as dysplastic.Statistical analysis was performed with SPSS for Windows, version 17.0. P<0.05 was considered to indicate a statistically significant difference.The normal range of the pituitary gland volumes was expressed as the mean ± standard deviation. The paired t-test was used to evaluate the repetition test, while Pearson’s correlation coefficient and regression analyses were performed to evaluate the correlations between the volume and height of the pituitary glands. Results:In the repetition tests, no statistically significant difference was observed between the two measurements of any observer (paired t-test; P=0.164; power of test, 1-β>0.8). Similarly, no statistically significant difference was observed between the measurements of the two observers (P=0.182; power of test, 1-β>0.8).To examine the association between pituitary gland volume and height with age, MRI was performed on 75 healthy children. The pituitary gland exhibited an increasing growth trend in volume over age. A growth spurt in the volume of the pituitary gland was observed in children aged between 10 and 14 years-old, and this trend was more prominent in females (P<0.05). By contrast, the height of the pituitary gland exhibited a gradual increase without a growth spurt.The correlation coefficient (r) and adjusted determination coefficient (R2) were 0.893 and 0.795 between the pituitary gland volume and age, as determined by correlation analysis. The r and R2 were 0.749 and 0.556 between the height and age.The r and R2 were 0.661 and 0.437, respectively, between the pituitary gland volume and height.To investigate the effectiveness of pituitary gland volume and height in detecting GHD or ISS, MRI was conducted on 32 children with GHD and 23 children with ISS. In the 32 children with GHD,21 individuals had pituitary gland volumes below the minimum value of the corresponding normal range, and the rate of hypoplastic pituitary gland volume was 65.6%. In the 23 children with ISS, eight individuals had pituitary gland volumes below the minimum value of the corresponding normal range, and the rate of hypoplastic pituitary gland volume was 34.8%. The rate of hypoplastic pituitary gland height was 37.5% for children with GHD and 26.1% for those with ISS. These obser vations demonstrated that the rates of hypoplastic pituitary gland volume and height in children with GHD was higher compared with those in the children with ISS, indicating that pituitary gland volume was a superior indicator for the detection of GHD and ISS. Conclusions:3D MRI volumetry was used in the present study to elucidate the developmental characteristics of the pituitary gland in healthy children. The results indicated that the measurement of pituitary gland height was not able to replace volumetry in the assessment of pituitary gland size. Reference data provided by 3D MRI were valuable in the diagnosis of short stature children. However, the evaluation required an association with neuroimaging and clinical functional abnormalities of the pituitary gland. |
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