F De Keyzer

Magnetic resonance imaging of the fetal lung: a pictorial essay

Ultrasound, which is now a widely available and generally accepted, low-cost technique with real-time properties, is the screening investigation of choice in fetal medicine. However, enthusiasm for fetal prenatal magnetic resonance imaging (MRI) is rising, because of the absence of known biological risks, the increasing ease of performing of fetal MRI and the superb contrast resolution provided. Over the last 10 years, the technology has advanced dramatically. Fast imaging sequences have allowed better MRI visualization of the unborn patient than ever before. As a consequence, experience with fetal MRI is gradually expanding. We are beginning to appreciate the clinical conditions where fetal MRI can complement the ultrasound findings. Apart from the central nervous system, MRI of the fetal lung has received the most attention. Fetal MRI can be used to assess thoracic structural anomalies, lung development as well as maturation. The introduction of fetal therapy for severe lung hypoplasia, associated with congenital diaphragmatic hernia (CDH), has recently boosted the application. This review aims to highlight MRI techniques used to image the lungs of the unborn child and to point out their strengths and limitations in specific conditions.

Diffusion-weighted MRI in lungs of normal fetuses and those with congenital diaphragmatic hernia

To prospectively determine apparent diffusion coefficient (ADC) values of normally developing fetal lungs over gestation, as obtained by diffusion‐weighted (DW) magnetic resonance imaging (MRI) and to investigate its potential application in fetuses with congenital diaphragmatic hernia (CDH).

A diffusion-weighted template for gestational age-related apparent diffusion coefficient values in the developing fetal brain.

To determine the pattern of apparent diffusion coefficient (ADC) values in the normal fetal brain obtained with diffusion‐weighted images (DWI) on magnetic resonance imaging (MRI) as a template for normal brain development throughout gestation.

CT Density Measurement and H:H Ratio Are Useful in Diagnosing Acute Cerebral Venous Sinus Thrombosis

BACKGROUND AND PURPOSE: Brain CT is widely used to exclude or confirm acute cerebral venous sinus thrombosis. The purpose of this study was to assess the value of attenuation measurement and the H:H ratio on unenhanced brain CT scans in the diagnosis of acute cerebral venous sinus thrombosis. MATERIALS AND METHODS: This retrospective study evaluated 20 patients with acute cerebral venous sinus thrombosis and 20 age- and sex-matched control participants without thrombosis. Three experienced observers independently evaluated the unenhanced brain CT scan for the presence of cerebral venous sinus thrombosis and measured the attenuation in the dural sinuses. Interreader differences were examined, as well as densities and H:H ratio between patients with acute cerebral venous sinus thrombosis and control participants. RESULTS: A significant difference in the average sinus attenuation was found between patients with acute cerebral venous sinus thrombosis (73.9 ± 9.2 HU) and the control group (52.8 ± 6.7 HU; P < .0001). A similar difference was found for the H:H ratio (1.91 ± 0.32 vs 1.33 ± 0.12 in patients with and without cerebral venous sinus thrombosis, respectively; P < .0001). Optimal thresholds of 62 HU and 1.52 lead to accuracies of 95% for average sinus attenuation and 97.5% for the H:H ratio, respectively. CONCLUSIONS: Hyperattenuation and the H:H ratio in the dural sinuses on unenhanced brain CT scans have a high accuracy in the detection of acute cerebral venous sinus thrombosis.

Diffusion-Weighted Imaging of the Head and Neck in Healthy Subjects: Reproducibility of ADC Values in Different MRI Systems and Repeat Sessions

BACKGROUND AND PURPOSE: DWI is typically performed with EPI sequences in single-center studies. The purpose of this study was to determine the reproducibility of ADC values in the head and neck region in healthy subjects. In addition, the reproducibility of ADC values in different tissues was assessed to identify the most suitable reference tissue. MATERIALS AND METHODS: We prospectively studied 7 healthy subjects, with EPI and TSE sequences, on 5 MR imaging systems at 3 time points in 2 institutions. ADC maps of EPI (with 2 b-values and 6 b-values) and TSE sequences were compared. Mean ADC values for different tissues (submandibular gland, sternocleidomastoid muscle, spinal cord, subdigastric lymph node, and tonsil) were used to evaluate intra- and intersubject, intersystem, and intersequence variability by using a linear mixed model. RESULTS: On 97% of images, a region of interest could be placed on the spinal cord, compared with 87% in the tonsil. ADC values derived from EPI-DWI with 2 b-values and calculated EPI-DWI with 2 b-values extracted from EPI-DWI with 6 b-values did not differ significantly. The standard error of ADC measurement was the smallest for the tonsil and spinal cord (standard error of measurement = 151.2 × 10−6 mm/s2 and 190.1 × 10−6 mm/s2, respectively). The intersystem difference for mean ADC values and the influence of the MR imaging system on ADC values among the subjects were statistically significant (P < .001). The mean difference among examinations was negligible (ie, <10 × 10−6 mm/s2). CONCLUSIONS: In this study, the spinal cord was the most appropriate reference tissue and EPI-DWI with 6 b-values was the most reproducible sequence. ADC values were more precise if subjects were measured on the same MR imaging system and with the same sequence. ADC values differed significantly between MR imaging systems and sequences.

T2 quantifications of fetal lungs at MRI-normal ranges

To prospectively determine the pattern of lung intensities and T2 values in fetuses with normally developing lungs as obtained with T2‐weighted single‐shot turbo spin echo magnetic resonance (TSE MR) imaging. This should serve as a reference to which images from fetuses with lung development disorders are compared.

Whole-body diffusion-weighted MRI for staging of women with cancer during pregnancy: a pilot study.

Methods Twenty patients diagnosed with cancer during pregnancy underwent WB-DWI additional to conventional imaging in this prospective single centre study. Reproducibility of WB-DWI between 2 readers was evaluated using Cohen’s statistics and accuracy was compared to conventional imaging for assessing primary tumour site, nodal metastases and visceral metastases. Histopathology after surgery or biopsy was the primary reference standard.

Whole-body diffusion-weighted imaging for staging lymphoma: are apparent diffusion coefficient derived histogram parameters useful for lesion characterisation?

Methods Fifteen patients with histopathology proven lymphoma (11 Non-Hodgkin; 4 Hodgkin lymphomas) underwent WB-DWI using 2 b-values (0-1000 s/mm). On coronal reformatted b1000 WB-DWI images, regions of interest (ROI) were drawn semi-automatically on lymph nodes in all nodal stations (n=267) and in axial and appendicular bone regions (n=53). For each ROI, a histogram was constructed from which volume, mean(ADC), median (ADC), skewness(ADC), and kurtosis(ADC) were calculated. Mann-Whitney-U tests were performed to detect significant differences between malignant and benign ROIs per tissue type. Receiver-operating-characteristic curves (ROC) were constructed from which an optimal threshold was determined as well as sensitivity, specificity and accuracy. PET/CT plus bone marrow biopsy (BMB) served as reference standard.

PD-0418: The use of diffusion weighted MRI in the prediction of volumetric changes during radiotherapy

Purpose/Objective: Concurrent chemoradiotherapy (CRT) is standard of care for patients with locally advanced head and neck squamous cell carcinoma (HNSCC). The current delineation and treatment planning approach uses a unique set of CT images. As a result, the volume change of the gross tumor volume (GTV) during RT is not considered. This could lead to changes in the initial dose distribution. Adaptive RT (ART) could counteract this problem. However, there is currently no way to identify suitable patients for ART. Diffusion weighted (DWI) MRI characterizes tissues based on the random displacement of water protons; quantified using the apparent diffusion coefficient (ADC). The aim of this study is to investigate if DWI is predictive for volumetric changes during RT and can help in the selection of patients suitable for ART. Materials and Methods: 59 patients with HNSCC with an initial tumor volume above 15 cc were included. We have chosen this limitation because we believe that the volumetrical changes in tumors smaller than 15 cc would have no or very small repercussions on initial dose distribution. RT was delivered to a dose of 72 Gy (20 x 2 Gy daily, followed by 20 x 1, 6 Gy twice daily). Patients received an MRI (1,5 Tesla) before RT, 2 and 4 weeks after start of RT. ADC values were determined using six b-values 0, 50, 150, 500, 750 and 1000 s/mm2. Volumes were determined on T1weighted MRI at all time-points. Pretreatment ADC values were correlated with the volumetric change in the tumor at 2 and 4 weeks during RT in all 59 patients. In 20 of these patients ΔADC values at 2 weeks were correlated with the volumetric changes at 4 weeks. To determine the strength of the correlation a Pearson correlation coefficient was used. A p-value ≤0.05 was considered to be statistically significant. Results: There was a significantly positive correlation between pretreatment ADC value and volumetric change at 2 weeks during RT (r=0.9; p=0.001). A positive correlation was also found with the volumetric changes at 4 weeks, however this failed to reach significance (r=0.4; p:0.08). No correlation was found between the ΔADC value at 2 weeks during RT and the volumetric changes at 4 weeks (r2:0.001; p:0.9). Conclusions: The implementation of ART is limited due to its time consuming nature and the inability to select suitable patients. We investigated in 59 patients diagnosed with HNSCC (with a tumor volume above 15 cc) if DWI characteristics could help us in this regard. We saw a positive correlation between pretreatment ADC value and the anatomical changes of the tumor during RT. Patients with a lower pretreatment ADC value appear to have a greater volume decrease early during RT, which might be useful in the selection of patient who might benefit from ART. We will set up a study in the future to validate these results in a bigger patient group and to investigate the potential role of other functional imaging techniques such as dynamic contrast enhanced magnetic resonance imaging (DCE-MRI).

Value of pretreatment MRI determined parameters for predicting outcome after radio-frequency ablation of hepatocellular carcinoma

Methods Thirty-seven patients with HCC treated by RFA were evaluated. Lesion number, size and segmental location, T2-weighted (w), arterial, portal-venous and venous contrast-phase, b600 diffusion-w imaging (DWI) and delayed phase contrast-enhanced imaging pattern were assessed at MRI. The separate imaging patterns as well as pretreatment clinical variables were correlated with outcome (disease free survival longer or shorter than 1 year) using a chi-square test with multiple variables and Mann-Whitney U test respectively. Pretreatment clinical variables and imaging parameters were correlated with Keratin 19 and microvascular invasion status at the biopsy during RFA.