An encounter-based approach for restricted diffusion with a gradient drift

We develop an encounter-based approach for describing restricted diffusion with a gradient drift towards a partially reactive boundary. For this purpose, we introduce an extension of the Dirichlet-to-Neumann operator and use its eigenbasis to derive a spectral decomposition for the full propagator, i.e., the joint probability density function for the particle position and its boundary local time. This is the central quantity that determines various characteristics of diffusion-influenced reactions such as conventional propagators, survival probability, first-passage time distribution, boundary local time distribution, and reaction rate. As an illustration, we investigate the impact of a constant drift onto the boundary local time for restricted diffusion on an interval. More generally, this approach accesses how external forces may influence the statistics of encounters of a diffusing particle with the reactive boundary.

Imaging features of intrahepatic cholangiocarcinoma mimicking a liver abscess: an analysis of 8 cases

Background In rare cases, intrahepatic cholangiocarcinoma can present as a pyogenic liver abscess and are often misdiagnosed. This study aimed to analyze the imaging features of intrahepatic cholangiocarcinoma mimicking a pyogenic liver abscess. Methods The clinical data and imaging results of eight patients with pathologically confirmed intrahepatic cholangiocarcinoma mimicking a liver abscess were retrospectively collected. Results The mean age was 58 years with a range of 46–68 years. Fever and leukocytosis were present in six patients. All the eight lesions were a single mass. Air–liquid levels were present in two patients. Only one patient showed hepatic lobar atrophy and hepatic capsule retraction. The double target sign of liver abscess was not noticed in the CT/MRI images of all eight patients. The inner wall of the lesion was rough and irregular, with multiple dot/patchy and wall nodule enhancements. The abscess wall and the marginal parenchyma were supplied by the hepatic artery in four patients, and the intralesional arteries were rough and disrupted. Bile duct dilatation was seen adjacent to the lesion. In seven patients, diffusion-weighted images showed irregular patchy restricted diffusion in the marginal parenchyma of the necrotic area in addition to the prominent restricted diffusion in the necrotic area. Two patients with cholangiolithiasis showed patchy slight CT hypodensity, slight T1 hypointensity, slight T2 hyperintensity, and patchy delayed enhancement. Multiple lymph nodes enlargement in the hepatic hilar area and the retroperitoneal space were seen in five patients. Conclusion Intrahepatic cholangiocarcinoma mimicking a pyogenic liver abscess have unique imaging features and require careful image examination to avoid misdiagnosis.

The centrally restricted diffusion sign on MRI for assessment of radiation necrosis in metastases treated with stereotactic radiosurgery

Purpose Differentiation of radiation necrosis from tumor progression in brain metastases treated with stereotactic radiosurgery (SRS) is challenging. For this, we assessed the performance of the centrally restricted diffusion sign. Methods Patients with brain metastases treated with SRS who underwent a subsequent intervention (biopsy/resection) for a ring-enhancing lesion on preoperative MRI between 2000 and 2020 were included. Excluded were lesions containing increased susceptibility limiting assessment of DWI. Two neuroradiologists classified the location of the diffusion restriction with respect to the post-contrast T1 images as centrally within the ring-enhancement (the centrally restricted diffusion sign), peripherally correlating to the rim of contrast enhancement, both locations, or none. Measures of diagnostic accuracy and 95% CI were calculated for the centrally restricted diffusion sign. Cohen's kappa was calculated to identify the interobserver agreement. Results Fifty-nine patients (36 female; mean age 59, range 40 to 80) were included, 36 with tumor progression and 23 with radiation necrosis based on histopathology. Primary tumors included 34 lung, 12 breast, 5 melanoma, 3 colorectal, 2 esophagus, 1 head and neck, 1 endometrium, and 1 thyroid. The centrally restricted diffusion sign was seen in 19/23 radiation necrosis cases (sensitivity 83% (95% CI 63 to 93%), specificity 64% (95% CI 48 to 78%), PPV 59% (95% CI 42 to 74%), NPV 85% (95% CI 68 to 94%)) and 13/36 tumor progression cases (difference p < 0.001). Interobserver agreement was substantial, at 0.61 (95% CI 0.45 to 70.8). Conclusion We found a low probability of radiation necrosis in the absence of the centrally restricted diffusion sign.

Acute spinal cord ischemic stroke; A rare but potentially devastating stroke emergency in young healthy adults

Introduction: Acute spinal cord infarction represents 1% of all strokes. The neurological presentation of spinal cord infarction is defined by vascular territory i.e. anterior or posterior spinal arteries. A broad spectrum of diseases can cause spinal cord infarction, most common cause is surgical repair or diseases of the thoracoabdominal aorta. MRI of the spine shows hyperintensities on T2WI, restricted diffusion on DWI and vertebral body infarction adjacent to a cord signal abnormality. Poor prognostic factors for recovery are severe impairment at presentation, female sex, advanced age, and lack of improvement in the first 24 hours. We describe clinical presentation, radiological findings and 3-month outcome of four patients who presented with ischemic spinal cord infarction. Methods: We retrospectively analysed our prospectively collected data and found four cases of spinal cord infarction for the period of May 2020 to April 2021. Total of 1,326 stroke patients (1125 i.e. 85% ischemic and 201 i.e. 15% haemorrhagic) were admitted in Hamad General Hospital. At our centre, spinal cord infarction accounts 0.30% of total stroke and 0.35% of ischemic strokes. We describe four young patients, presented with abrupt onset of focal neurologic deficit. Their MRI of the spine revealed hyperintensity signals in T2WI, restricted diffusion on DWI of spinal cord. Two patients had vertebral artery occlusion or dissection. One patient was discharged home and three patients underwent multidisciplinary rehabilitation program. Discussion: Spinal cord infarction may present with acute paraparesis or quadriparesis with devastating consequences. Blood flow to the spinal cord is influenced by perfusion pressure. The most common cause of spinal cord infarction in this case series was vertebral artery dissection or occlusion. Our case series suggests early recognition of spinal cord stroke, appropriate investigations and early treatment with further rehabilitation could improve patient outcome. Conclusion: Spinal cord infarction, a rare but devastating condition, represents 1% of all strokes but 0.3% of total strokes at our centre. Early recognition of spinal cord ischemia especially when presenting with abrupt onset focal neurological deficit, focus on underlying pathology with appropriate imaging and further investigations, secondary stroke prevention and rehabilitation are vital factors to improve neurological recovery. Future randomized trails are needed to establish the efficacy and safety of drug therapy including rt-PA in spinal cord infarction. Abbreviations: ASA: Anterior spinal artery; PSA: Posterior spinal artery; MRI: Magnetic resonance imaging; MRA: Magnetic resonance arteriogram; DWI: Diffusion weighted imaging; ICP: Intra-cranial pressure.

All that glitters are not gold: holds true in female adnexal lesions

Background Adnexal mass lesions are commonly encountered pathologies that creates diagnostic challenges for radiologist. Diffusion weighted imaging is a vital tool in the radiologist armamentarium for improving the diagnostic accuracy of adnexal lesions other than routine spine echo sequences. Main body Functional information about the lesion regarding the mobility of the water molecules in its tissue is assessed by diffusion weighted imaging. In addition to the solid malignant neoplasm, normal blood, fat, necrosis and pus also shows restricted diffusion. Conclusion All the lesion that shows restriction in the DWI are not malignant, but converse is mostly true. Knowledge regarding the non-malignant lesion in the ovary that shows restricted diffusion will give a clue in diagnosis, management and treatment of the adnexal lesions.