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1.
M E Miquel A D Scott N D Macdougall R Boubertakh N Bharwani A G Rockall 《The British journal of radiology》2012,85(1019):1507-1512
Objective
To study the in vitro and in vivo (abdomen) variability of apparent diffusion coefficient (ADC) measurements at 1.5 T using a free-breathing multislice diffusion-weighted (DW) MRI sequence.Methods
DW MRI images were obtained using a multislice spin-echo echo-planar imaging sequence with b-values=0, 100, 200, 500, 750 and 1000 s mm−2. A flood-field phantom was imaged at regular intervals over 100 days, and 10 times on the same day on 2 occasions. 10 healthy volunteers were imaged on two separate occasions. Mono-exponential ADC maps were fitted excluding b=0. Paired analysis was carried out on the liver, spleen, kidney and gallbladder using multiple regions of interest (ROIs) and volumes of interest (VOIs).Results
The in vitro coefficient of variation was 1.3% over 100 days, and 0.5% and 1.0% for both the daily experiments. In vivo, there was no statistical difference in the group mean ADC value between visits for any organ. Using ROIs, the coefficient of reproducibility was 20.0% for the kidney, 21.0% for the gallbladder, 24.7% for the liver and 28.0% for the spleen. For VOIs, values fall to 7.7%, 6.4%, 8.6% and 9.6%, respectively.Conclusion
Good in vitro repeatability of ADC measurements provided a sound basis for in vivo measurement. In vivo variability is higher and when considering single measurements in the abdomen as a whole, only changes in ADC value greater than 23.1% would be statistically significant using a two-dimensional ROI. This value is substantially lower (7.9%) if large three-dimensional VOIs are considered.Diffusion-weighted (DW) MRI is based on the Brownian motion of water in biological tissues [1,2]. The technique has played a preponderant role in neuro-imaging over the last two decades and it is known to detect small changes before they are apparent on anatomical imaging [3,4].In recent years DW MRI has been increasingly used in other parts of the body, demonstrating great diagnostic potential in cancer imaging. To date, DW MRI has been successfully used for tissue characterisation and tumour staging. However, the apparent diffusion coefficient (ADC) is a potential biomarker that could be used to monitor treatment response or evaluate post-therapeutic changes. Details of the clinical use of DW MRI can be found in the 2009 consensus paper [5] or in general and organ-specific review articles [6-8].While DW MRI is a potentially powerful tool in diagnostic oncology, the lack of uniform protocols for imaging and data analysis hinder its clinical implementation. Large differences in ADC values are reported in the literature depending on the acquisition parameters, in particular the choice of b-values (e.g. see [9] for ADC values in the kidney or 5] highlighted the importance of quality analysis, validation and reproducibility studies. Although there are some emerging reproducibility and repeatability data in the abdomen [15,19-22], a recent review by Taouli and Koh [7] highlights the need for further work in this area. Recently, coefficients of variability of around 14% were published for both solid tumours [22] and bone marrow [23]. Other studies seem to indicate that only ADC changes of over 27% [20] or 30% [21] are significant. Substantial variations in ADC values have also been found between different scanners and vendors [24-26], further highlighting the difficulty of setting up multicentre trials.Table 1
Apparent diffusion coefficient values measured in normal liver at 1.5 TReference | Mean ADC (10−3 mm2 s−1) | Standard deviation | Range | Number of subjects | b-values (s mm−2) | Comments |
Taouli et al [10] | 1.60 | 0.13 | 1.44–1.88 | 10 v | 0, 500 | Conventional |
1.52 | 0.15 | 1.28–180 | With parallel imaging | |||
1.51 | 0.21 | 1.27–1.99 | Diffusion tensor/parallel imaging | |||
Mürtz et al [11] | 0.92–0.96a | 0.09–0.14 | 0.62–1.20 | 12 v | 50, 300, 700, 1000, 1300 | Pulse triggered |
1.03–1.14 | 0.22–0.40 | 0.67–2.57 | Non-triggered | |||
Kim et al [12] | 1.05/1.02b | 0.30/0.25 | 6 v/126 p | 3, 57, 192, 408, 517, 850 | ||
1.55/1.16 | 0.37/0.42 | 3, 57, 192, 408, 192, 408 | ||||
4.8/3.55 | 2.37/1.75 | 3, 57 | ||||
Ichikawa et al [13] | 2.28 | 1.23 | 46 p | 1.6, 55 | ||
Taouli et al [14] | 1.83 | 0.36 | 1.4–2.55 | 66 p | 0, 500 | |
1.51 | 0.49 | 1.12–2.71 | 0, 134, 267, 400 | |||
Kwee et al [15] | 1.60/1.62/1.57c | 0.14/0.18/0.15 | 11 v | 0, 500 | Breath-hold | |
2.13/2.27/2.07 | 0.33/0.47/0.43 | Respiratory triggered | ||||
1.65/1.62/1.65 | 0.09/0.16/0.17 | Free breathing (7 mm slice) | ||||
1.64/1.66/1.57 | 0.13/0.11/0.19 | Free breathing (5 mm slice) | ||||
Yamada et al [16] | 0.87 | 0.26 | 78 p | 30, 300, 900,1100 | ADC | |
0.76 | 0.27 | Diffusion coefficient (DC) | ||||
Müller et al [17] | 1.39 | 0.16 | 10 v+9 p | 8 b-values; bmax 328–454 | ||
Namimato et al [18] | 0.69 | 0.31 | 51 p | 30, 1200 | ||
This study | 1.04 | 0.05 | 0.95–1.11 | 10 v | 100, 200, 500, 750, 1000 | Free breathing |
2.
A Granata L Zanoli S Clementi P Fatuzzo P Di Nicolò F Fiorini 《The British journal of radiology》2014,87(1038)
In renal diagnosis, the B-mode ultrasound is used to provide an accurate study of the renal morphology, whereas the colour and power Doppler are of strategic importance in providing qualitative and quantitative information about the renal vasculature, which can also be obtained through the assessment of the resistive index (RI). To date, this is one of the most sensitive parameters in the study of kidney diseases and allows us to quantify the changes in renal plasma flow. If a proper Doppler ultrasound examination is carried out and a critical analysis of the values obtained is performed, the RI measurement at the interlobar artery level has been suggested in the differential diagnosis between nephropathies. The aim of this review is to highlight the pathological conditions in which the study of intrarenal RI provides useful information about the pathophysiology of renal diseases in both the native and the transplanted kidneys.Renal ultrasonography has acquired a strategic importance in the early detection of several renal diseases thanks to its non-invasivity, low cost, reliability and high sensitivity. The B-mode ultrasound is a widely used technique for the study of kidney morphology, including renal pelvis, to provide information on parenchymal echogenicity and to detect space-occupying lesions.The characteristic ultrasonographic pattern in chronic kidney disease (small kidneys, reduced parenchymal thickness and detection of cysts) allows a simple and accurate diagnosis of this pathological condition. On the other hand, the diagnostic validity of the B-mode ultrasound in the detection of acute renal disease is still under debate because of the lack of sensitivity and specificity of the commonly used parameters such as the increase of renal size and the reduction of the parenchymal echogenicity.The advantage of using Doppler ultrasound (DUS) lies in its ability in detecting not only renal morphological abnormalities but also functional ones; colour Doppler, power DUS and spectral analysis provide qualitative and quantitative haemodynamic information about the intrarenal and extrarenal vasculature highlighting changes in the renal blood flow.The measure of renal resistive index (RI) or Pourcelot index is one of the most sensitive parameters in the study of disease-derived alterations of renal plasma flow.The aim of this review is to evaluate the significance of the renal RI as a non-invasive marker of renal histological damage in several pathological conditions (Clinical setting RI Proposed clinical value All nephropathies >0.75 Indicator of tubulointerstitial nephropathy1 AKI >0.75 Useful in discriminating between ATN and pre-renal form2 Chronic renal failure >0.80 Indicator of irreversible damage >0.70 Independent risk factor for worsening function3–6 Renal colic >0.70 Signs of complete ureteral obstruction7,8 ∆RI > 0.08–0.10 Kidney transplantation >0.80 In SKT graft, unfavourable prognostic factor9 >0.80 Association with recipient survival10 >0.75 Long-term RF for NODAT11 Diabetes Type 1—children 7–15 years old >0.64 Risk factor for diabetic nephropathy12 Type 2 >0.70 Indicator of advanced glomerular lesions and/or arteriosclerotic lesions13 >0.73 Predictor of DN and its progression14 Renal artery stenosis >0.80 Poor renal improvement after PTA15 Cirrhosis >0.78 Risk factor for HRS12