What magnetic resonance imaging reveals - A systematic review of the relationship between type II diabetes and associated brain distortions of structure and cognitive functioning.

Due to its increasing prevalence, Type 2 diabetes mellitus (T2DM) represents a major health challenge for modern society. Despite it being of fundamental interest, only a few MRI studies have conducted statistical analyses to draw scientifically valid conclusions about the complex interplay of T2DM and its associated clinical, structural, functional, metabolite, as well as cognitive distortions. Therefore, a systematic review of 68 manuscripts, following the PRISMA guidelines, was conducted. Notably, although the associations between imaging, clinical, and cognitive variables are not fully homogeneous, findings show a clear trend towards a link between altered brain structure and a decline in cognitive processing ability. The results of the review highlight the heterogeneity of the methods used across manuscripts in terms of assessed clinical variables, imaging, and data analysis methods. This is particularly significant as, if the subjects' criteria are not carefully considered, results are easily prone to confounding factors.

Age-dependency of glycosaminoglycan content in lumbar discs: A 3t gagcEST study.

PURPOSE: To analyze age-dependency of glycosaminoglycan content using gagCEST (glycosaminoglycan chemical exchange saturation transfer) imaging in lumbar intervertebral discs of healthy volunteers. MATERIALS AND METHODS: In all, 70 volunteers without low back pain (mean age 44 ± 14 years, range: 21-69 years) were examined with T2 -weighted and gagCEST imaging with a 3T MR scanner, with approval of the local Ethics Committee after written informed consent was obtained. Pfirrmann grading and classification into discs without bulging and herniation, discs with bulging, and discs with herniation were performed. Only intervertebral discs without bulging and herniation were analyzed. A region-of-interest-based gagCEST analysis of nucleus pulposus (NP) and annulus fibrosus (AF) was performed. Correlation between age and gagCEST was tested within groups of equal Pfirrmann score. RESULTS: GagCEST effects decreased significantly from 3.09 ± 1.12% in 20-29 years old volunteers to -0.24 ± 1.36% in 50-59 years old volunteers (P < 0.001). In the case of Pfirrmann scores 2 and 3, a significant correlation was observed between gagCEST effect and age (Pfirrmann score 2, NP: ρ = -0.558, P < 0.001; Pfirrmann score 3, NP: ρ = -0.337, P = 0.048). For Pfirrmann scores 1 and 4, no significant correlation was obtained (Pfirrmann score 1, NP: ρ = -0.046, P = 0.824; Pfirrmann score 4, NP: ρ = -0.316, P = 0.188). CONCLUSION: We show a decreased gagCEST effect likely corresponding to decreasing glycosaminoglycans with aging. Hence, age-matched analysis of gagCEST imaging may be necessary in future studies.

Comparison of quantitative and semiquantitative dynamic contrast-enhanced MRI with respect to their correlation to delayed gadolinium-enhanced MRI of the cartilage in patients with early rheumatoid arthritis.

OBJECTIVE: The objective of this study was to investigate the correlation between semiquantitative and quantitative dynamic contrast-enhanced (DCE) parameters with delayed gadolinium-enhanced magnetic resonance imaging (MRI) of the cartilage (dGEMRIC). METHODS: Fifteen patients with early rheumatoid arthritis (RA) from the ArthroMark cohort were investigated at a 3-T MRI scanner. The metacarpophalangeal (MCP) joint of the index finger was examined with DCE-MRI and dGEMRIC. Semiquantitative and quantitative DCE perfusion parameters were calculated. The RA MRI score of the second MCP joint and the joint space width were measured. RESULTS: Significant correlations were noted between both semiquantitative and quantitative DCE parameters and the RA MRI score of the second MCP joint. There was a significant negative correlation between DCE parameters and dGEMRIC. No association between joint space width and DCE parameters was observed. CONCLUSIONS: Semiquantitative and quantitative analyses of perfusion are applicable to show that cartilage damage correlates with the inflammation activity despite the absence of joint space narrowing.

Improvement of gagCEST imaging in the human lumbar intervertebral disc by motion correction.

OBJECTIVE: To investigate whether motion correction improves glycosaminoglycan chemical exchange saturation transfer imaging (gagCEST imaging) of intervertebral discs (IVDs). MATERIALS AND METHODS: Magnetic resonance gagCEST imaging of 12 volunteers was obtained in lumbar IVDs at 3 T using a prototype pulse sequence. The data were motion-corrected using a prototype diffeomorphism-based motion compensation technique. For both the data with and that without motion correction (datac, datauc), CEST evaluation was performed using the magnetisation transfer ratio asymmetry (MTRasym) as a means of quantifying CEST effects. MTRasym and the signal-to-noise ratio (SNR) of the MTRasym map in the nucleus pulposus (NP) were compared for datac and datauc. A visual grading analysis was performed by a radiologist in order to subjectively quantify the quality of the MTRasym analysis (score 1: best quality, score 5: worst quality). Furthermore, a landmark analysis was performed in order to objectively quantify the motion between CEST images using the mean landmark distance dmean. RESULTS: MTRasym and SNR were significantly higher for the motion-corrected data than for the uncorrected CEST data (MTRasym(datac) = 3.77 % ± 0.95 %, MTRasym(datauc) = 3.41 % ± 1.54 %, p value = 0.001; SNR(datac) = 3.88 ± 2.04, SNR(datauc) = 2.77 ± 1.55, p value < 0.001, number of IVDs = 48). The visual grading analysis revealed a higher reliability for datac (maximum score = 2) compared with datauc (maximum score = 5). The landmark analysis demonstrated the superiority of the motion-corrected data (dmean(datac) = 0.08 mm ± 0.09 mm, dmean(datauc) = 0.36 mm ± 0.09 mm, p value = 0.001). CONCLUSION: Our study showed significant improvements in the ability to quantify CEST imaging in IVDs after the application of motion correction compared with uncorrected datasets.

Pilot study of Iopamidol-based quantitative pH imaging on a clinical 3T MR scanner.

OBJECTIVE: The objective of this study was to show the feasibility to perform Iopamidol-based pH imaging via clinical 3T magnetic resonance imaging (MRI) using chemical exchange saturation transfer (CEST) imaging with pulse train presaturation. MATERIALS AND METHODS: The pulse train presaturation scheme of a CEST sequence was investigated for Iopamidol-based pH measurements using a 3T magnetic resonance (MR) scanner. The CEST sequence was applied to eight tubes filled with 100-mM Iopamidol solutions with pH values ranging from 5.6 to 7.0. Calibration curves for pH quantification were determined. The dependence of pH values on the concentration of Iopamidol was investigated. An in vivo measurement was performed in one patient who had undergone a previous contrast-enhanced computed tomography (CT) scan with Iopamidol. The pH values of urine measured with CEST MRI and with a pH meter were compared. RESULTS: In the measured pH range, pH imaging using CEST imaging with pulse train presaturation was possible. Dependence between the pH value and the concentration of Iopamidol was not observed. In the in vivo investigation, the pH values in the human bladder measured by the Iopamidol CEST sequence and in urine were consistent. CONCLUSION: Our study shows the feasibility of using CEST imaging with Iopamidol for quantitative pH mapping in vitro and in vivo on a 3T MR scanner.

Kidney transplant: functional assessment with diffusion-tensor MR imaging at 3T.

PURPOSE: To evaluate the feasibility of diffusion-tensor (DT) imaging at 3 T for functional assessment of transplanted kidneys. MATERIALS AND METHODS: This study was approved by the local ethics committee; written informed consent was obtained. Between August 2009 and October 2010, 40 renal transplant recipients were prospectively included in this study and examined with a clinical 3-T magnetic resonance (MR) imager. An echo-planar DT imaging sequence was performed in coronal orientation by using five b values (0, 200, 400, 600, 800 sec/mm(2)) and 20 diffusion directions. The fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were determined for the cortex and medulla of the transplanted kidney. Relationships between FA, ADC, and allograft function, determined by the estimated glomerular filtration rate (eGFR), were assessed by using Pearson correlation coefficient. ADC and FA were compared between patients with good or moderate allograft function (group A; eGFR > 30 mL/min/1.73 m(2)) and patients with impaired function (group B; eGFR ≤ 30 mL/min/1.73 m(2)) by using a student t test. P < .05 indicated a statistically significant difference. RESULTS: Mean FA of the renal medulla and cortex was significantly higher in group A (0.39 ± 0.06 and 0.17 ± 0.4) compared with group B (0.27 ± 0.05 and 0.14 ± 0.03) (P < .001 and P = .009, respectively). Mean ADCs of renal cortex and medulla were significantly higher in group A than in group B (P = .007 and P = .01, respectively). In group B, mean medullary FA was significantly lower in patients whose renal function did not recover (0.22 ± 0.02) compared with those with stable allograft function at 6 months (0.29 ± 0.05, P < .001). There was significant correlation between eGFR and medullary FA (r = 0.65, P < .001), cortical ADC (r = 0.43, P = .003), and medullary ADC (r = 0.35, P = .01). CONCLUSION: DT imaging is a promising noninvasive technique for functional assessment of renal allografts. FA values in the renal medulla exhibit a good correlation with renal function.

Impact of blood flow on diffusion coefficients of the human kidney: a time-resolved ECG-triggered diffusion-tensor imaging (DTI) study at 3T.

PURPOSE: To evaluate the impact of renal blood flow on apparent diffusion coefficients (ADC) and fractional anisotropy (FA) using time-resolved electrocardiogram (ECG)-triggered diffusion-tensor imaging (DTI) of the human kidneys. MATERIALS AND METHODS: DTI was performed in eight healthy volunteers (mean age 29.1 ± 3.2) using a single slice coronal echoplanar imaging (EPI) sequence (3 b-values: 0, 50, and 300 s/mm(2)) at the timepoint of minimum (20 msec after R wave) and maximum renal blood flow (200 msec after R wave) at 3T. Following 2D motion correction, region of interest (ROI)-based analysis of cortical and medullary ADC- and FA-values was performed. RESULTS: ADC-values of the renal cortex at maximum blood flow (2.6 ± 0.19 × 10(-3) mm(2)/s) were significantly higher than at minimum blood flow (2.2 ± 0.11 × 10(-3) mm(2)/s) (P < 0.001), while medullary ADC-values did not differ significantly (maximum blood flow: 2.2 ± 0.18 × 10(-3) mm(2)/s; minimum blood flow: 2.15 ± 0.14 × 10(-3) mm(2)/s). FA-values of the renal medulla were significantly greater at maximal blood (0.53 ± 0.05) than at minimal blood flow (0.47 ± 0.05) (P < 0.01). In contrast, cortical FA-values were comparable at different timepoints of the cardiac cycle. CONCLUSION: ADC-values in the renal cortex as well as FA-values in the renal medulla are influenced by renal blood flow. This impact has to be considered when interpreting renal ADC- and FA-values.

Biexponential analysis of diffusion-weighted imaging: comparison of three different calculation methods in transplanted kidneys.

BACKGROUND: Biexponential analysis has been used increasingly to obtain contributions of both diffusion and microperfusion to the signal decay in diffusion-weighted imaging DWI of different parts of the body. PURPOSE: To compare biexponential diffusion parameters of transplanted kidneys obtained with three different calculation methods. MATERIAL AND METHODS: DWI was acquired in 15 renal allograft recipients (eight men, seven women; mean age, 52.4 ± 14.3 years) using a paracoronal EPI sequence with 16 b-values (b = 0-750 s/mm(2)) and six averages at 1.5T. No respiratory gating was used. Three different calculation methods were used for the calculation of biexponential diffusion parameters: Fp, ADCP, and ADCD were calculated without fixing any parameter a priori (calculation method 1); ADCP was fixed to 12.0 µm(2)/ms, whereas Fp and ADCD were calculated using the biexponential model (calculation method 2); multistep approach with monoexponential fitting of the high b-value portion (b ≥ 250 s/mm(2)) for determination of ADCD and assessment of the low b intercept for determination of Fp (calculation method 3). For quantitative analysis, ROI measurements were performed on the according parameter maps. RESULTS: Mean ADCD values of the renal cortex using calculation method 1 were significantly lower than using calculation methods 2 and 3 (P < 0.001). There was a significant correlation between calculation methods 1 and 2 (r = 0.69 (P < 0.005) and calculation methods 1 and 3 (r = 0.59; P < 0.05) as well as calculation methods 2 and 3 (r = 0.98; P < 0.001). Mean Fp values of the renal cortex were higher with calculation method 1 than with calculation methods 2 and 3 (P < 0.001). For Fp, only the correlation between calculation methods 2 and 3 was significant (r = 0.98; P < 0.001). CONCLUSION: Biexponential diffusion parameters differ significantly depending on the calculation methods used for their calculation.

Diffusion kurtosis imaging of the human kidney: a feasibility study.

PURPOSE: To assess the feasibility and to optimize imaging parameters of diffusion kurtosis imaging (DKI) in human kidneys. METHODS: The kidneys of ten healthy volunteers were examined on a clinical 3T MR scanner. For DKI, respiratory triggered EPI sequences were acquired in the coronal plane (3 b-values: 0, 300, 600s/mm(2), 30 diffusion directions). A goodness of fit analysis was performed and the influence of the signal-to-noise ratio (SNR) on the DKI results was evaluated. Region-of-interest (ROI) measurements were performed to determine apparent diffusion coefficient (ADC), fractional anisotropy (FA) and mean kurtosis (MK) of the cortex and the medulla of the kidneys. Intra-observer and inter-observer reproducibility using Bland-Altman plots as well as subjective image quality of DKI were examined and ADC, FA, and MK parameters were compared. RESULTS: The DKI model fitted better to the experimental data (r=0.99) with p<0.05 than the common mono-exponential ADC model (r=0.96). Calculation of reliable kurtosis parameters in human kidneys requires a minimum SNR of 8.31 on b=0s/mm(2) images. Corticomedullary differentiation was possible on FA and MK maps. ADC, FA and MK revealed significant differences in medulla (ADC=2.82 × 10(-3)mm(2)/s±0.25, FA=0.42±0. 05, MK=0.78±0.07) and cortex (ADC=3.60 × 10(-3)mm(2)/s±0.28, FA=0.18±0.04, MK=0.94±0.07) with p<0.001. CONCLUSION: Our initial results indicate the feasibility of DKI in the human kidney presuming an adequate SNR. Future studies in patients with kidney diseases are required to determine the value of DKI for functional kidney imaging.

Feasibility of diffusional kurtosis tensor imaging in prostate MRI for the assessment of prostate cancer: preliminary results.

PURPOSE: To assess the feasibility of full diffusional kurtosis tensor imaging (DKI) in prostate MRI in clinical routine. Histopathological correlation was achieved by targeted biopsy. MATERIALS AND METHODS: Thirty-one men were prospectively included in the study. Twenty-one were referred to our hospital with increased prostate specific antigen (PSA) values (>4ng/ml) and suspicion of prostate cancer. The other 10 men were volunteers without any history of prostate disease. DKI applying diffusion gradients in 20 different spatial directions with four b-values (0, 300, 600, 1000s/mm(2)) was performed additionally to standard functional prostate MRI. Region of interest (ROI)-based measurements were performed in all histopathologically verified lesions of every patient, as well as in the peripheral zone, and the central gland of each volunteer. RESULTS: DKI showed a substantially better fit to the diffusion-weighted signal than the monoexponential apparent diffusion coefficient (ADC). Altogether, 29 lesions were biopsied in 14 different patients with the following results: Gleason score 3+3=6 (n=1), 3+4=7 (n=7), 4+3=7 (n=6), 4+4=8 (n=1), and 4+5=9 (n=2), and prostatitis (n=12). Values of axial (Kax) and mean kurtosis (Kmean) were significantly different in the tumor (Kax 1.78±0.39, Kmean 1.84±0.43) compared with the normal peripheral zone (Kax 1.09±0.12, Kmean 1.16±0.13; p<0.001) or the central gland (Kax 1.40±0.12, Kmean 1.44±0.17; p=0.01 respectively). There was a minor correlation between axial kurtosis (r=0.19) and the Gleason score. CONCLUSION: Full DKI is feasible to utilize in a routine clinical setting. Although there is some overlap some DKI parameters can significantly distinguish prostate cancer from the central gland or the normal peripheral zone. Nevertheless, the additional value of DKI compared with conventional monoexponential ADC calculation remains questionable and requires further research.

Temporally resolved electrocardiogram-triggered diffusion-weighted imaging of the human kidney: correlation between intravoxel incoherent motion parameters and renal blood flow at different time points of the cardiac cycle.

PURPOSE: To evaluate the influence of pulsatile blood flow on apparent diffusion coefficients (ADC) and the fraction of pseudodiffusion (F(P)) in the human kidney. MATERIALS AND METHODS: The kidneys of 6 healthy volunteers were examined by a 3-T magnetic resonance scanner. Electrocardiogram (ECG)-gated and respiratory-triggered diffusion-weighted imaging (DWI) and phase-contrast flow measurements were performed. Flow imaging of renal arteries was carried out to quantify the dependence of renal blood flow on the cardiac cycle. ECG-triggered DWI was acquired in the coronal plane with 16 b values in the range of 0 s/mm(2) and 750 s/mm(2) at the time of minimum (MIN) (20 milliseconds after R wave) and maximum renal blood flow (MAX) (197 ± 24 milliseconds after R wave). The diffusion coefficients were calculated using the monoexponential approach as well as the biexponential intravoxel incoherent motion model and correlated to phase-contrast flow measurements. RESULTS: Flow imaging showed pulsatile renal blood flow depending on the cardiac cycle. The mean flow velocity at MIN was 45 cm/s as compared with 61 cm/s at MAX. F(p) at MIN (0.29) was significantly lower than at MAX (0.40) (P = 0.001). Similarly, ADC(mono), derived from the monoexponential model, also showed a significant difference (P < 0.001) between MIN (ADC(mono) = 2.14 ± 0.08 × 10(-3) mm(2)/s) and MAX (ADC(mono) = 2.37 ± 0.04 × 10(-3) mm(2)/s). The correlation between renal blood flow and F(p) (r = 0.85) as well as ADC(mono) (r = 0.67) was statistically significant. CONCLUSION: Temporally resolved ECG-gated DWI enables for the determination of the diffusion coefficients at different time points of the cardiac cycle. ADC(mono) and FP vary significantly among acquisitions at minimum (diastole) and maximum (systole) renal blood flow. Temporally resolved ECG-gated DWI might therefore serve as a novel technique for the assessment of pulsatility in the human kidney.