Random Motion Of Water Molecules Research Articles

Radiofrequency Enhancer to Recover Signal Dropouts in 7 Tesla Diffusion MRI.

Diffusion magnetic resonance imaging (dMRI) allows for a non-invasive visualization and quantitative assessment of white matter architecture in the brain by characterizing restrictions on the random motion of water molecules. Ultra-high field MRI scanners, such as those operating at 7 Tesla (7T) or higher, can boost the signal-to-noise ratio (SNR) to improve dMRI compared with what is attainable at conventional field strengths such as 3T or 1.5T. However, wavelength effects at 7T cause reduced transmit magnetic field efficiency in the human brain, mainly in the posterior fossa, manifesting as signal dropouts in this region. Recently, we reported a simple approach of using a wireless radiofrequency (RF) surface array to improve transmit efficiency and signal sensitivity at 7T. In this study, we demonstrate the feasibility and effectiveness of the RF enhancer in improving in vivo dMRI at 7T. The electromagnetic simulation results demonstrated a 2.1-fold increase in transmit efficiency with the use of the RF enhancer. The experimental results similarly showed a 1.9-fold improvement in transmit efficiency and a 1.4-fold increase in normalized SNR. These improvements effectively mitigated signal dropouts in regions with inherently lower SNR, such as the cerebellum, resulting in a better depiction of principal fiber orientations and an enhanced visualization of extended tracts.

MRI with generalized diffusion encoding reveals damaged white matter in patients previously hospitalized for COVID-19 and with persisting symptoms at follow-up.

There is mounting evidence of the long-term effects of COVID-19 on the central nervous system, with patients experiencing diverse symptoms, often suggesting brain involvement. Conventional brain MRI of these patients shows unspecific patterns, with no clear connection of the symptomatology to brain tissue abnormalities, whereas diffusion tensor studies and volumetric analyses detect measurable changes in the brain after COVID-19. Diffusion MRI exploits the random motion of water molecules to achieve unique sensitivity to structures at the microscopic level, and new sequences employing generalized diffusion encoding provide structural information which are sensitive to intravoxel features. In this observational study, a total of 32 persons were investigated: 16 patients previously hospitalized for COVID-19 with persisting symptoms of post-COVID condition (mean age 60 years: range 41-79, all male) at 7-month follow-up and 16 matched controls, not previously hospitalized for COVID-19, with no post-COVID symptoms (mean age 58 years, range 46-69, 11 males). Standard MRI and generalized diffusion encoding MRI were employed to examine the brain white matter of the subjects. To detect possible group differences, several tissue microstructure descriptors obtainable with the employed diffusion sequence, the fractional anisotropy, mean diffusivity, axial diffusivity, radial diffusivity, microscopic anisotropy, orientational coherence (Cc) and variance in compartment's size (CMD) were analysed using the tract-based spatial statistics framework. The tract-based spatial statistics analysis showed widespread statistically significant differences (P < 0.05, corrected for multiple comparisons using the familywise error rate) in all the considered metrics in the white matter of the patients compared to the controls. Fractional anisotropy, microscopic anisotropy and Cc were lower in the patient group, while axial diffusivity, radial diffusivity, mean diffusivity and CMD were higher. Significant changes in fractional anisotropy, microscopic anisotropy and CMD affected approximately half of the analysed white matter voxels located across all brain lobes, while changes in Cc were mainly found in the occipital parts of the brain. Given the predominant alteration in microscopic anisotropy compared to Cc, the observed changes in diffusion anisotropy are mostly due to loss of local anisotropy, possibly connected to axonal damage, rather than white matter fibre coherence disruption. The increase in radial diffusivity is indicative of demyelination, while the changes in mean diffusivity and CMD are compatible with vasogenic oedema. In summary, these widespread alterations of white matter microstructure are indicative of vasogenic oedema, demyelination and axonal damage. These changes might be a contributing factor to the diversity of central nervous system symptoms that many patients experience after COVID-19.

Multidimensional Diffusion MRI Methods With Confined Subdomains

Diffusion Magnetic Resonance Imaging (dMRI) is an imaging technique with exquisite sensitivity to the microstructural properties of heterogeneous media. The conventionally adopted acquisition schemes involving single pulsed field gradients encode the random motion of water molecules into the NMR signal, however typically conflating the effects of different sources contributing to the water motion. Time-varying magnetic field gradients have recently been considered for disentangling such effects during the data encoding phase, opening to the possibility of adding specificity to the recovered information about the medium’s microstructure. Such data is typically represented via a diffusion tensor distribution (DTD) model, thus assuming the existence of several non-exchanging compartments in each of which diffusion is unrestricted. In this work, we consider a model that takes confinement into account and possesses a diffusion time-dependence closer to that of restricted diffusion, to replace the free diffusion assumption in multidimensional diffusion MRI methods. We first demonstrate how the confinement tensor model captures the relevant signal modulations impressed by water diffusing in both free and closed spaces, for data simulated with a clinically feasible protocol involving time-varying magnetic field gradients. Then, we provide the basis for incorporating this model into two multidimensional dMRI methods, and attempt to recover a confinement tensor distribution (CTD) on a human brain dataset.

Diffusion Kurtosis Imaging-A Superior Approach to Assess Tumor-Stroma Ratio in Pancreatic Ductal Adenocarcinoma.

Extensive desmoplastic stroma is a hallmark of pancreatic ductal adenocarcinoma (PDAC) and contributes to tumor progression and to the relative resistance of tumor cells towards (radio) chemotherapy. Thus, therapies that target the stroma are under intense investigation. To allow the stratification of patients who would profit from such therapies, non-invasive methods assessing the stroma content in relation to tumor mass are required. In the current prospective study, we investigated the usefulness of diffusion-weighted magnetic resonance imaging (DW-MRI), a radiologic method that measures the random motion of water molecules in tissue, in the assessment of PDAC lesions, and more specifically in the desmoplastic tumor stroma. We made use of a sophisticated DW-MRI approach, the so-called diffusion kurtosis imaging (DKI), which possesses potential advantages over conventional and widely used monoexponential diffusion-weighted imaging analysis (cDWI). We found that the diffusion constant D from DKI is highly negatively correlated with the percentage of tumor stroma, the latter determined by histology. D performed significantly better than the widely used apparent diffusion coefficient (ADC) from cDWI in distinguishing stroma-rich (>50% stroma percentage) from stroma-poor tumors (≤50% stroma percentage). Moreover, we could prove the potential of the diffusion constant D as a clinically useful imaging parameter for the differentiation of PDAC-lesions from non-neoplastic pancreatic parenchyma. Therefore, the diffusion constant D from DKI could represent a valuable non-invasive imaging biomarker for assessment of stroma content in PDAC, which is applicable for the clinical diagnostic of PDAC.

Short-term increase in discs\u2019 apparent diffusion is associated with pain and mobility improvements after spinal mobilization for low back pain

Pain perception, trunk mobility and apparent diffusion coefficient (ADC) within all lumbar intervertebral discs (IVDs) were collected before and shortly after posterior-to-anterior (PA) mobilizations in 16 adults with acute low back pain. Using a pragmatic approach, a trained orthopaedic manual physical therapist applied PA mobilizations to the participants’ spine, in accordance with his examination findings. ADCall was computed from diffusion maps as the mean of anterior (ADCant), middle (ADCmid), and posterior (ADCpost) portions of the IVD. After mobilization, pain ratings and trunk mobility were significantly improved and a significant increase in ADCall values was observed. The greatest ADCall changes were observed at the L3-L4 and L4-L5 levels and were mainly explained by changes in ADCant and ADCpost, respectively. No significant changes in ADC were observed at L5-S1 level. The reduction in pain and largest changes in ADC observed at the periphery of the hyperintense IVD region suggest that increased peripheral random motion of water molecules is implicated in the IVD nociceptive response modulation. Additionally, ADC changes were observed at remote IVD anatomical levels that did not coincide with the PA spinal mobilization application level.

Associations between apparent diffusion coefficient and electromyography parameters in myositis-A preliminary study.

Objective MRI is widely used in several muscle disorders. Diffusion‐weighted imaging (DWI) is an emergent imaging modality sensitive to microstructural alterations in tissue. The apparent diffusion coefficient (ADC) is used to quantify the random motion of water molecules. Electromyography (EMG) is a clinically used diagnostic tool in myositis. The aim of this study was to elucidate possible associations between ADC values and EMG findings in myositis patients.MethodSeven patients (eight investigated muscles) with myositis (mean age 51.43 ± 19 years) were included in this study. The diagnosis was confirmed by histopathology in every case. DWI was obtained with a 1.5‐T scanner using two b‐values 0 and 1000 s/mm². In all patients, a needle electromyography (EMG) was performed within 3 days to the MRI. The following EMG parameters were studied: motor unit action potential (MUAP) amplitudes and durations, as well as pathological spontaneous activity. Spearman's correlation coefficient was used to analyze associations between investigated parameters.ResultsThe estimated mean ADC mean value was 1.51 ± 0.29 × 10−3 mm²/s, mean ADC min was 1.28 ± 0.27 × 10−3 mm²/s, and mean ADC max was 1.73 ± 0.28 × 10−3 mm²/s. Correlation analysis identified significant associations between ADC mean and duration of the MUAP (p = .78 P = .0279) and between ADC min and duration of the MUAP (p = .85, P = .01). There were no significant differences according to pathological spontaneous activity.Conclusion ADC mean and ADC min showed strong positive correlations with the duration of the MUAP in myositis patients. Both modalities might similarly reflect muscle fiber loss in myositis patients.

Non-Invasive Prostate Cancer Characterization with Diffusion-Weighted MRI: Insight from In silico Studies of a Transgenic Mouse Model.

Diffusion-weighted magnetic resonance imaging (DWI) enables non-invasive, quantitative staging of prostate cancer via measurement of the apparent diffusion coefficient (ADC) of water within tissues. In cancer, more advanced disease is often characterized by higher cellular density (cellularity), which is generally accepted to correspond to a lower measured ADC. A quantitative relationship between tissue structure and in vivo measurements of ADC has yet to be determined for prostate cancer. In this study, we establish a theoretical framework for relating ADC measurements with tissue cellularity and the proportion of space occupied by prostate lumina, both of which are estimated through automatic image processing of whole-slide digital histology samples taken from a cohort of six healthy mice and nine transgenic adenocarcinoma of the mouse prostate (TRAMP) mice. We demonstrate that a significant inverse relationship exists between ADC and tissue cellularity that is well characterized by our model, and that a decrease of the luminal space within the prostate is associated with a decrease in ADC and more aggressive tumor subtype. The parameters estimated from our model in this mouse cohort predict the diffusion coefficient of water within the prostate-tissue to be 2.18 × 10−3 mm2/s (95% CI: 1.90, 2.55). This value is significantly lower than the diffusion coefficient of free water at body temperature suggesting that the presence of organelles and macromolecules within tissues can drastically hinder the random motion of water molecules within prostate tissue. We validate the assumptions made by our model using novel in silico analysis of whole-slide histology to provide the simulated ADC (sADC); this is demonstrated to have a significant positive correlation with in vivo measured ADC (r2 = 0.55) in our mouse population. The estimation of the structural properties of prostate tissue is vital for predicting and staging cancer aggressiveness, but prostate tissue biopsies are painful, invasive, and are prone to complications such as sepsis. The developments made in this study provide the possibility of estimating the structural properties of prostate tissue via non-invasive virtual biopsies from MRI, minimizing the need for multiple tissue biopsies and allowing sequential measurements to be made for prostate cancer monitoring.

On the Vanishing of the t-term in the Short-Time Expansion of the Diffusion Coefficient for Oscillating Gradients in Diffusion NMR

Nuclear magnetic resonance (NMR) diffusion measurements can be used to probe porous structures or biological tissues by means of the random motion of water molecules. The short-time expansion of the diffusion coefficient in powers of sqrt(t), where t is the diffusion time related to the duration of the diffusion-weighting magnetic field gradient profile, is universally connected to structural parameters of the boundaries restricting the diffusive motion. The sqrt(t)-term is proportional to the surface to volume ratio. The t-term is related to permeability and curvature. The short time expansion can be measured with two approaches in NMR-based diffusion experiments: First, by the use of diffusion encodings of short total duration and, second, by application of oscillating gradients of long total duration. For oscillating gradients, the inverse of the oscillation frequency becomes the relevant time scale. The purpose of this manuscript is to show that the oscillating gradient approach is blind to the t-term. On the one hand, this prevents fitting of permeability and curvature measures from this term. On the other hand, the t-term does not bias the determination of the sqrt(t)-term in experiments.

Apparent diffusion coefficient (ADC) does not correlate with different serological parameters in myositis and myopathy.

Background Magnetic resonance imaging (MRI) is widely used in several muscle disorders. Diffusion-weighted imaging (DWI) is an imaging modality, which can reflect microstructural tissue composition. The apparent diffusion coefficient (ADC) is used to quantify the random motion of water molecules in tissue. Purpose To investigate ADC values in patients with myositis and non-inflammatory myopathy and to analyze possible associations between ADC and laboratory parameters in these patients. Material and Methods Overall, 17 patients with several myositis entities, eight patients with non-inflammatory myopathies, and nine patients without muscle disorder as a control group were included in the study (mean age = 55.3 ± 14.3 years). The diagnosis was confirmed by histopathology in every case. DWI was obtained in a 1.5-T scanner using two b-values: 0 and 1000 s/mm2. In all patients, the blood sample was acquired within three days to the MRI. The following serological parameters were estimated: C-reactive protein, lactate dehydrogenase, alanine aminotransferase, aspartate aminotransferase, creatine kinase, and myoglobine. Results The estimated mean ADC value for the myositis group was 1.89 ± 0.37 × 10-3 mm2/s and for the non-inflammatory myopathy group was 1.79 ± 0.33 × 10-3 mm2/s, respectively. The mean ADC values (1.15 ± 0.37 × 10-3 mm2/s) were significantly higher to unaffected muscles (vs. myositis P = 0.0002 and vs. myopathy P = 0.0021). There were no significant correlations between serological parameters and ADC values. Conclusion Affected muscles showed statistically significantly higher ADC values than normal muscles. No linear correlations between ADC and serological parameters were identified.

Differentiation of Osteoporotic and Neoplastic Vertebral Fractures by Chemical Shift {In-Phase and Out-of Phase} Magnetic Resonance Imaging and Diffusion Weighted Sequence

In elderly population neoplastic wedging of the spine may be an early manifestation of underlying malignancy and differentiating benign wedging due to underlying osteoporosis from malignant wedging has been an important and sought after goal of imaging. Other challenging clinical case scenario is the occurrence of benign osteoporotic vertebral collapse in a patient already known to have underlying malignancy .Although magnetic resonance imaging (MRI) is a sensitive method for assessing bone marrow, it lacks specificity. The problem is that abnormal signal intensity in benign compression fractures on conventional MR imaging can be similar to that seen in vertebrae with underlying malignancy. Although certain morphologic signs may be helpful for assessing the cause of the fracture yet these lack specificity. The presence of both fat and water in normal marrow results in suppression of signal intensity on the opposed-phase images. In benign osteoporotic collapse, no marrow replacement has occurred, thus the existence of normal marrow fat should result in suppression of signal intensity on the opposed-phase images; while in malignant collapse the normal fat-containing marrow is replaced with tumoral process which should result in lack of suppression on the opposed phase images. Diffusion-weighted sequences are sensitive to molecular motion because random motion of water molecules in gradient fields produces phase dispersion and, therefore, signal attenuation. The current review will focus on the advent of both modalities and the value to order them in proper clinical setting.

ADHD and Cerebellar Vermis Tumor: DTI Analysis of an Incidental Finding

The increase in number of magnetic resonance imaging (MRI) scans for investigation of neurological diseases in childhood and adolescence leads to increase of incidental findings of central nervous system (CNS) tumors in these stages of life. Among MRI techniques, diffusion-weighted imaging (DWI) and diffusion tensor imaging (DTI) have been increasingly used in brain studies. These images are based on random motion of water molecules in the body, which can change depending on constitution and geometry of biological tissues, as well as the existence of pathologies. This paper reports the use of DTI and DWI to evaluation of a CNS tumor incidentally detected in a patient diagnosed previously with Attention Deficit Hyperactivity Disorder (ADHD). He was diagnosed at age 9 and has been treated with medicines and psycho-pedagogical therapies. At age 15 a MRI detected a cerebellar vermis tumor with a volume of 2 cm 3 . Due to parental decision, the patient did not undergo any surgical intervention. During the follow-up period we did not observe significant changes in tumor size or diffusion directions in the tumor and surrounding brain tissues. The main brain tracts presented normal diffusion patterns, both in terms of size and geometry. The DTI analysis showed that lesion was quite homogeneous and isotropic, with no significant restriction of diffusion. There also were no significant diffusion pattern changes in other regions of the brain which possibly could be related to ADHD. So, given the characteristics of lesion and the patient's clinical symptoms, it cannot be directly related to ADHD.

Diffusion Magnetic Resonance Imaging: What Water Tells Us about Biological Tissues.

Since its introduction in the mid-1980s, diffusion magnetic resonance imaging (MRI), which measures the random motion of water molecules in tissues, revealing their microarchitecture, has become a pillar of modern neuroimaging. Its main clinical domain has been the diagnosis of acute brain stroke and neurogical disorders, but it is also used in the body for the detection and management of cancer lesions. It can also produce stunning maps of white matter tracks in the brain, with the potential to aid in the understanding of some psychiatric disorders. However, in order to exploit fully the potential of this method, a deeper understanding of the mechanisms that govern the diffusion of water in tissues is needed.

Nanoblinker: Brownian motion powered bio-nanomachine for FRET detection of phagocytic phase of apoptosis.

We describe a new type of bio-nanomachine which runs on thermal noise. The machine is solely powered by the random motion of water molecules in its environment and does not ever require re-fuelling. The construct, which is made of DNA and vaccinia virus topoisomerase protein, can detect DNA damage by employing fluorescence. It uses Brownian motion as a cyclic motor to continually separate and bring together two types of fluorescent hairpins participating in FRET. This bio-molecular oscillator is a fast and specific sensor of 5′OH double-strand DNA breaks present in phagocytic phase of apoptosis. The detection takes 30 s in solution and 3 min in cell suspensions. The phagocytic phase is critical for the effective execution of apoptosis as it ensures complete degradation of the dying cells’ DNA, preventing release of pathological, viral and tumor DNA and self-immunization. The construct can be used as a smart FRET probe in studies of cell death and phagocytosis.

Difüzyon Ağırlıklı Manyetik Rezonans Görüntülemenin Benign ve Malign Adrenal Lezyonları Ayırt Etmedeki Değeri

Objective: Diffusion weighted imaging (DWI) is a functional magnetic resonance imaging (MRI) technique that explores the random motion of water molecules in the body. Although DWI has been widely applied in the evaluation of intracranial disorders, there is growing interest for its use in detection and characterization of abdominal masses. In this study, the efficiency of DWI in distinguishing benign adrenal focal lesions from malignant ones is investigated. Material and Methods: Sixty six adrenal focal lesions in 56 patients were included in the study. The lesions were characterized with dynamic adrenal computed tomography and/or adrenal MRI if there was not a histopathological result or radiological follow up. DWI was performed for these lesions and apparent diffusion coefficient (ADC) values were measured by using three different b values (b=500 sec/mm2, b=750 sec/mm2, b=1000 sec/mm2). Results: The mean ADC values of 39 benign lesions were 1.54 x 10-3 mm2/sec for b=500 sec/mm2, 1.01x 10-3 mm2/sec for b=750 sec/mm2 and 0.77 x 10-3 mm2/sec for b=1000 sec/mm2. The mean ADC values of 27 malignant lesions were found to be 1.69x 10-3 mm2/sec, 1.14 x 10-3 mm2/sec and 0.86 x 10-3 mm2/sec for b=500 sec/mm2, b=750 sec/mm2, b=1000 sec/mm2, respectively. There was not any statistically significant difference between ADC values of benign and malignant lesions for all three b values (p

Spurious group differences due to head motion in a diffusion MRI study

Diffusion-weighted MRI (DW-MRI) has become a popular imaging modality for probing the microstructural properties of white matter and comparing them between populations in vivo. However, the contrast in DW-MRI arises from the microscopic random motion of water molecules in brain tissues, which makes it particularly sensitive to macroscopic head motion. Although this has been known since the introduction of DW-MRI, most studies that use this modality for group comparisons do not report measures of head motion for each group and rely on registration-based correction methods that cannot eliminate the full effects of head motion on the DW-MRI contrast. In this work we use data from children with autism and typically developing children to investigate the effects of head motion on differences in anisotropy and diffusivity measures between groups. We show that group differences in head motion can induce group differences in DW-MRI measures, and that this is the case even when comparing groups that include control subjects only, where no anisotropy or diffusivity differences are expected. We also show that such effects can be more prominent in some white-matter pathways than others, and that they can be ameliorated by including motion as a nuisance regressor in the analyses. Our results demonstrate the importance of taking head motion into account in any population study where one group might exhibit more head motion than the other.

DIFFUSION MR CORRELATES OF MOTOR FUNCTION RECOVERY AFTER STROKE: A SYSTEMATIC REVIEW

BackgroundCorticospinal tract (CST) integrity predicts the capacity for motor recovery after stroke and can be studied by diffusion–weighted MRI (DWI) sequences which measure random motion of water molecules along multiple...

Diffusion tensor imaging of formalin fixed infarcted porcine hearts

Background Diffusion is the random motion exhibited by molecules as a result of thermal agitation. In biological tissues the random motion of water molecules is anisotropic since they are restricted by the tissue structure. The application of diffusion tensor imaging (DTI) makes it possible to quantify the amount of diffusion in tissues. Further processing allows a 3D visualization of the fiber architecture by tracking the fiber trajectories within a tissue. Experimental evidence has shown that fiber architecture in the myocardium changes with the onset of myocardial infarction [1]. Furthermore, the myocardium undergoes remodeling as the infarction progresses over time. The aim of this study is to evaluate the remodeling of the fiber architecture in an infarcted porcine heart. Methods

ADC measurements in diffuse large B-cell lymphoma and follicular lymphoma: a DWI and cellularity study

PurposeDiffusion-weighted magnetic resonance imaging (DW-MRI) allows quantifying the random motion of water molecules in tissue by means of apparent diffusion coefficient (ADC) measurements. The aim of the study was to determine whether ADC measurements allow discrimination of diffuse large B-cell lymphoma (DLBCL) from follicular lymphoma (FL), and to examine the relationship between cellularity and ADC value of the tumor using DWI. Materials and methodsThirty-two patients with histologically proven non-Hodgkin lymphoma (21 with DLBCL and 11 with FL, 17 males and 15 females, mean age 62±13 years) underwent conventional MRI and DWI examination before treatment. The ADC values of DLBCL were compared to those of FL. The ADC value of the tumor was also correlated with the tumor tissue cellularity. ResultsThe mean ADC value of DLBCL was not significantly different from that of FL (0.70±0.16×10−3mm2/s vs. 0.76±0.12×10−3mm2/s, P=0.21). The cellularity of DLBCL was significantly lower than that of FL (2991±351 cells/view vs. 4412±767 cells/view, P<0.001). There was no correlation between the ADC value and the tissue cellularity of the tumor in patients with DLBCL and FL. ConclusionADC measurements could not differentiate between DLBCL and FL, and there was no correlation between the ADC value and cellularity of the tumor in patients with DLBCL and FL.

Pretransplant prediction of microvascular invasion in patients with hepatocellular carcinoma: Added value of diffusion-weighted magnetic resonance imaging

The goals of the meticulous selection of patients withhepatocellular carcinoma (HCC) for liver transplanta-tion (LT) are to minimize the incidence of tumor recur-rence after transplantation and to improve patients’survival. Tumor invasion into vascular structures is aknown risk factor for tumor recurrence after LT. Mac-rovascular invasion, which is defined as the presenceof a tumor thrombus in a hepatic or portal vein, canbe detected on preoperative cross-sectional imaging. Itis considered an absolute contraindication to LT. Con-versely, microvascular invasion (MVI) by definitioncan be definitively diagnosed only by histopathology.Several studies have shown that MVI is associatedwith HCC recurrence within 1 year of transplanta-tion.

Diffusion‐weighted MRI compared to FDG PET‐CT in the staging and response assessment of Hodgkin lymphoma

A 29-year-old man presented with a large right supraclavicular mass, weight loss and night sweats. A diagnosis of stage 4B nodular sclerosis Hodgkin lymphoma was made. F-fluorodeoxyglucose positron emission tomography with computed tomography (FDG PET-CT) and whole-body magnetic resonance imaging with diffusion-weighting (DW-MRI) were performed before and after escalated BEACOPP (bleomycin, etoposide, doxorubicin, cyclophosphamide, vincristine, procarbazine, prednisone) chemotherapy. The pre-treatment FDG PET-CT (top left) demonstrated extensive nodal disease above and below the diaphragm, including the right supraclavicular fossa. Post-treatment FDG PET-CT (top right) showed physiological FDG uptake only. The pre-treatment DW-MRI (bottom left) showed extensive nodal disease in the same distribution as the pre-treatment FDG PET-CT. DW-MRI revealed a bone lesion (arrow) not diagnosed on the FDG PET-CT, confirmed on the source axial images. Post-treatment morphological MRI (not shown) demonstrated residual nodal disease in the right lower neck and upper abdomen but this was all inactive on DW-MRI (bottom right). FDG PET-CT and DW-MRI independently established a complete response. FDG PET-CT is a recommended imaging method for determining disease activity in residual masses after treatment for Hodgkin lymphoma. There is an increasing body of evidence to support its use in the assessment of early response to chemotherapy and it has been established as reliable for staging Hodgkin lymphoma. However, it involves radiation exposure for both the CT and FDG components of the test. MRI does not use ionizing radiation and offers higher soft tissue contrast compared with CT. The reduction of exposure to ionizing radiation is of particular significance in patients with lymphoma who have a high chance of cure, especially in younger patients. Water diffusion whole body MRI also allows functional assessment of lymphoma response. DW-MRI relies on measuring the random motion of water molecules in tissues. Many malignant tumours, including lymphomas, are more cellular than benign/normal tissue and therefore show more restricted water diffusion, appearing bright on normal images or dark on inverted images such as those shown above. The disadvantages of MRI include the exclusion of patients with pacemakers, implantable defibrillators or significant claustrophobia. In addition, bulk tissue movements and physiological water motion can sometimes affect DW-MRI image quality. In general, FDG PET-CT is accurate for diagnosis of marrow and bone involvement in Hodgkin lymphoma but, in this case, DW-MRI revealed bone disease not diagnosed on FDG PETCT. Further research is needed to compare the relative merits of DW whole-body MRI with FDG PET-CT in the staging and monitoring of lymphoma.