Purpose To assess cardiac motion-induced signal loss in diffusion-weighted magnetic resonance imaging (DWI) of the liver using dynamic DWI. Materials and methods Three volunteers underwent dynamic coronal DWI of the liver under breathholding, in the diastolic (DWI diast ) or systolic (DWI syst ) cardiac phase, and with motion probing gradients (MPGs) in phase encoding (P, left-right), frequency encoding (M, superior-inferior), or slice select (S, anterior-posterior) direction. Liver-to-background contrasts (LBCs) of DWI syst were compared to those of DWI diast , for both the left and right liver lobes, using nonparametric tests. Signal decrease ratios (SDRs) were calculated as (1 (median 3.35) were significantly lower (P < 0.0001) than those of DWI diast (median 4.84). In the right liver lobe, LBCs of DWI syst (median 4.17) were also significantly lower (P < 0.0001) than those of DWI diast (median 5.35). SDRs of the left and right liver lobes were 25.5% and 17.3%, respectively. In DWI syst , the significantly lowest (P < 0.05) LBCs were observed in the M direction (left liver lobe) and P direction (right liver lobe) of MPGs. Conclusion Signal intensity of both liver lobes are affected by cardiac motion in DWI. In the left liver lobe, signal loss especially occurs in the superior-inferior direction of MPGs, whereas in the right lobe, signal loss especially occurs in the left-right direction of MPGs.

18 F-FDG PET is an established functional imaging modality for the evaluation of human disease. Diffusion-weighted MRI (DWI) is another rapidly evolving functional imaging modality that can be used to evaluate oncologic and nononcologic lesions throughout the body. The information provided by 18 F-FDG PET and DWI can be complementary, because the 2 methods are based on completely different biophysical underpinnings. This article will describe the basic principles, clinical applications, and limitations of DWI. In addition, the available evidence that correlates and compares 18 F-FDG PET and DWI will be reviewed. PET,usi ng the radiotracer 18 F-FDG, is an established functional imaging modality for a variety of oncologic and nononcologic (e.g., inflammatory and infectious) applications (1-3). The contribution of 18 F-FDG PET to medicine has been unmatched by any other functional imaging modality (4). At present, there is also growing interest in the application of diffusion-weighted MRI (DWI) in the body (5-7). DWI allows visualization and quantification of the mobility of water molecules and has many potential clinical applications. Importantly, although 18 F-FDG PET and DWI are both functional imaging modalities and provide a high lesion-to-background contrast, they are based on completely different biophysical and biochemical underpinnings. Therefore, the information provided by the 2 imaging modalities may be regarded as complementary. Given the developing applications of DWI, the increasing use of multimodality imaging (8), and the expected advent of fully integrated PET/MRI systems (9), knowledge of the characteristics, possibilities, and limitations of DWI technique is becoming increasingly important. This is true for both the imaging specialists and the clinicians who use these modalities. This article will review the basic principles, clinical applications, and limitations of DWI. Furthermore, the available evidence that correlates and compares 18 F-FDG PET with DWI will be reviewed.

The purpose of this study was to determine if the apparent diffusion coefficient (ADC) on diffusion-weighted MRI could predict the response of patients with advanced pancreatic cancer to chemotherapy. Diffusion-weighted MRI was performed in 63 consecutive patients with advanced pancreatic cancer who were subsequently treated with chemotherapy. The ADC values of the primary tumour with a middle b-value (400 s mm(-2)) and a high b-value (1000 s mm(-2)) were determined; cystic or necrotic components were avoided. The patients were classified into two groups: (i) those with progressive disease and (ii) those who were stable 3 months and 6 months after initial treatment. The groups were compared with respect to the ADC and clinical factors, including gender, age, Union International Contre le Cancer (UICC ) stage, initial tumour size and chemotherapy agents used. Local tumour progression rates were evaluated using the Kaplan-Meier method. The middle b-value ADC of the pancreatic cancers ranged from 0.93-2.42 x10(-3) mm(2) s(-1) (mean, 1.50 x10(-3) mm(2) s(-1)), and the high b-value ADC ranged from 0.72-1.88 x10(-3) mm(2) s(-1) (mean, 1.20 x10(-3) mm(2) s(-1)). The high b-value ADC was significantly different between the progressive and stable groups at 3 months' and 6 months' follow-up (p = 0.03 and p = 0.04, respectively). The rate of tumour progression was significantly higher in those with a lower high b-value ADC than in those with a higher b-value ADC (median progression time, 140 days vs 182 days; p = 0.01). In conclusion, a lower high b-value ADC in patients with advanced pancreatic cancer may be predictive of early progression in chemotherapy-treated patients.

IntroductionPunctate white matter lesions (PWML) are recognized with magnetic resonance imaging (MRI) as hypersignal on T1-weighted imaging and hyposignal on T2-weighted imaging. Our aim was to assess how often a hemorrhagic component was present in PWML using susceptibility-weighted imaging (SWI).MethodsSeventeen preterm (gestational age, 25–34 weeks) and seven full-term infants (age at MRI, 37–42 weeks) with PWML were included. Seven preterm infants had sequential MRIs. PWML were diagnosed with conventional MRI and compared with SWI, where signal loss is suggestive of hemorrhage. The pattern of associated brain lesions was taken into account, and the percentage of lesions with signal loss on SWI was calculated for each infant.ResultsA significantly higher percentage of signal loss on SWI (median, 93.9%) was found among infants with germinal matrix and intraventricular hemorrhage as the primary diagnosis (n = 8) compared to those with a primary diagnosis of white matter injury (n = 14; median, 14.2%; p < 0.01). In the infants with serial MRIs, a reduction in the number of PWML and/or signal loss on SWI was noted at term equivalent age. In the patient who died, cystic lesions, associated with hemorrhage and gliosis, were demonstrated on histology.ConclusionsSWI can distinguish hemorrhagic and non-hemorrhagic PWML. Signal loss on SWI was more common when PWML were associated with an intraventricular hemorrhage. Longitudinal imaging showed a decrease in the number of PWML over time, with some PWML no longer showing signal loss on SWI, suggesting early gliosis.Electronic supplementary materialThe online version of this article (doi:10.1007/s00234-011-0872-0) contains supplementary material, which is available to authorized users.