Current status of body MR imaging: fast MR imaging and diffusion-weighted imaging

The recent technical advances in fast MR imaging have greatly enhanced the clinical value of MR imaging of the body. Advances in T₁-weighted images have enabled the acquisition of dynamic contrast-enhanced MR imaging, which is currently central to hepatic MR imaging for detection and characterization of liver tumors and is also useful for the evaluation of myometrial invasion in uterine cor-pus cancer. Advances in rapid T₂-weighted MR imaging with single-shot fast spin-echo images have enabled MR cholangiopancreatography and MR urography. Application of respiratory triggering can also provide T₂-weighted images of high quality. Cine MR imaging utilizing ultrafast MR sequences enables the assessment of the respiratory motion of the lung for evaluating thoracic wall invasion by tumors. Diffusion-weighted images can provide excellent tissue contrast based on molecular diffusion and have the potential to demonstrate malignant tumors. Quantitative measurement of apparent diffusion coefficient values may also be valuable in distinguishing malignancies from benign lesions.     

Imaging of Experimental Rat Gliomas Using a Clinical MR Scanner

Background: Studies of brain tumor development in experimental animal models have to date mostly been based on post-mortem histological examinations. The use of magnetic resonance imaging (MRI) may provide a non-invasive technique for studying tumor growth and treatment effects in such animal models. However, most of these studies have been performed on purpose-dedicated small bore magnetic resonance (MR) systems, of high cost and limited availability. The purpose of this study was thus to obtain high-resolution images of experimental gliomas in the rat brain, using a clinical 1.5T MR scanner. Methods: Anesthesized rats bearing BT₄C brain tumors were positioned into a specially designed immobilizing device, and a small circular coil was positioned onto the skulls. Two T1 weighted series were acquired before and after subcutaneous contrast injections. A T2 weighted series was also obtained. The rats were then sacrified, the brains removed, and the histological tumor volumes were compared to the volumes obtained on MRI. Results: There were visible tumors in 10 of 13 animals scanned on MR. The rim of the tumors were visualized on T1 weighted series without contrast. On T1 images with contrast, the tumors were seen as high signal intensity areas. The T2 weighted images showed peritumoral edema. No necrosis or cystic parts of the tumors were detected. There was a consistency between the MR and the histology findings, showing a high degree of correlation between the two volume determination methods. Conclusions: High-resolution images of experimental rat gliomas can be obtained using a clinical MR scanner and a commercially available RF coil. This MRI technique may also be expanded to extraneural rat tumor models, for studies of tumor development and treatment.     

Reliability of diffusion weighted MR imaging in differentiating degenerative and infectious end plate changes

Background

The aim of the study was to investigate the value of diffusion weighted MR imaging in the diagnosis of Modic type 1 change, which may be confused with the acute infectious spondylodiscitis on conventional MR imaging.

Patients and methods

Twenty-seven patients with erosive intervertebral osteochondrosis, Modic type 1 and 18 patients with spondylodiscitis were included in this retrospective study. All images were acquired using on 1.5 Tesla MR units. Lumbar spinal MR imaging of 45 patients were retrieved from a digital database of a radiology record system and evaluated by one experienced radiologist. Patients with Modic type 1 change had CT slices obtained from the diseased disc space and the affected vertebrae.

Results

Bone marrow adjacent to the vertebral end plate in both Modic type 1 change and acute spondylodiscitis were hypointense on T1-weighted images. On T2-weighted images corresponding levels of vertebral end-plates showed hyperintense signal intensity in both group. All the patients with spondylodiscitis and Modic type 1 change were hyperintense and hypointense on diffusion-weighted MR images, respectively.

Conclusions

Our findings suggest that diffusion weighted MR imaging is an useful method in differentiating Modic type 1 changes from acute spondylodiscitis, both of which may mimic each other, either on clinical or conventional MRI findings.     

Effects of combretastatin on murine tumours monitored by 31P MRS, 1H MRS and 1H MRI

Purpose: Combretastatins have tubulin-binding activity and are being investigated for their toxicity against tumour vasculature. We report the use of ³¹P and ¹H magnetic resonance (MR) spectroscopy and ¹H MR imaging for monitoring the effects of combretastatin A-4 prodrug (100mg/kg, i.p.) on energy metabolism and necrosis, respectively, in the C3H murine mammary tumour.Materials and Methods: The tumours (volume ca. 200mm³) were grown in the hind foot of mice. MR examinations were performed without anaesthesia within a 7.1 Tesla magnet. ³¹P MRS (TR = 6 s) was performed before treatment and at 1-, 2-, 3-, and 24-h after injection of drug or saline via an i.p. line. ¹H MRS (PRESS; 24μl voxel; TR = 2 s; TE = 135 ms) and both T₁-weighted (TR = 0.2 s; TE = 0.02 s) and T₂-weighted (TR = 2 s; TE = 0.20 s) ¹H MRI were performed before treatment and 2.5 and 24 h afterwards.Results: The ratio β-nucleotide triphosphate/inorganic phosphate fell by 33% within 1 h of treatment and remained constant for a further 2 h. A small but significant fall in pH (by 0.11 units) was observed at 1 h. Although an increase in the ¹H MR spectroscopy signal at about 1.32 ppm (predominantly from lactate) was observed in some tumours following combretastatin treatment, this effect was not seen consistently. No changes in the intensity of T₂-weighted ¹H MR images or in tumour necrosis (measured histologically) were detected within 3 h of treatment.Conclusions: The reduction in tumour energetics and pH was consistent with a reduction in tumour blood flow but this occurred before any significant incidence of haemorrhagic necrosis was detected. The combretastatin dose used to achieve these effects was less than one tenth of the maximum tolerated dose in mice.     

A method to convert MRI images of temperature change into images of absolute temperature in solid tumours

Abstract

Purpose: During hyperthermia (HT), the therapeutic response of tumours varies substantially within the target temperature range (39–43?°C). Current thermometry methods are either invasive or measure only temperature change, which limits the ability to study tissue responses to HT. This study combines manganese-containing low temperature sensitive liposomes (Mn-LTSL) with proton resonance frequency shift (PRFS) thermometry to measure absolute temperature in tumours with high spatial and temporal resolution using MRI.

Methods: Liposomes were loaded with 300?mM MnSO₄. The phase transition temperature (T_m) of Mn-LTSL samples was measured by differential scanning calorimetry (DSC). The release of manganese from Mn-LTSL in saline was characterised with inductively coupled plasma atomic emission spectroscopy. A 2T GE small animal scanner was used to acquire dynamic T₁-weighted images and temperature change images of Mn-LTSL in saline phantoms and fibrosarcoma-bearing Fisher-344 rats receiving hyperthermia after Mn-LTSL injection.

Results: The T_m of Mn-LTSL in rat blood was 42.9?±?0.2?°C (DSC). For Mn-LTSL samples (0.06?mM–0.5?mM Mn²⁺ in saline) heated monotonically from 30?°C to 50?°C, a peak in the rate of MRI signal enhancement occurred at 43.1°?±?0.3?°C. The same peak in signal enhancement rate was observed during heating of fibrosarcoma tumours (N?=?3) after injection of Mn-LTSL, and the peak was used to convert temperature change images into absolute temperature. Accuracies of calibrated temperature measurements were in the range 0.9–1.8?°C.

Conclusion: The release of Mn²⁺ from Mn-LTSL affects the rate of MR signal enhancement which enables conversion of MRI-based temperature change images to absolute temperature.     

椎管内囊性神经鞘瘤影像学特点

目的:研究MRI对椎管内囊性神经鞘瘤的诊断价值及鉴别诊断。方法:回顾性分析经病理证实的MR表现为椎管内囊性神经鞘瘤10例,6名男性,4名女性,年龄范围37~62岁,平均年龄51.4岁。结果:MRI显示病变均位于髓外硬膜下,T1WI表现为低信号,T2WI表现为高信号,增强扫描显示为环状强化。结论:MRI是诊断椎管内囊性神经鞘瘤的重要手段,其MR及增强扫描表现比较典型,对外科手术计划有很大帮助。由于其典型的强化特点鉴别诊断并不复杂。     

MRI to quantify early radiation-induced changes in the salivary glands

Purpose

We investigated radiation-induced changes in the salivary glands, 6 weeks after RT, using MRI.

Materials and methods

Eighteen oropharyngeal cancer patients were treated with salivary gland sparing IMRT. All patients received a 3T MRI exam before and 6 weeks after the end of RT, including a T₁-weighted (T₁w), a T₂-weighted (T₂w), and a dynamic contrast-enhanced (DCE) MRI.For both time points separately, the parotid and submandibular glands were delineated on the MR images. Differences in median signal intensity and signal variation within the glands were tested for significance. Correlations were studied between the MR changes and the planned RT dose.

Results

The volume of the glands reduced significantly by 25%. The T₁w signal decreased by 10% and the T₂w signal increased by 23%. The k_ep value decreased, while the v_e increased. A correlation of the changes in T₂w signal with the mean dose was found in both glands.

Conclusions

Overall radiation-induced changes and volume loss were observed in the parotid and submandibular gland using MR. The observed differences indicated an increased water content such as found in oedema. The overall changes could be related to the mean dose, with a slightly greater impact in the high dose area.     

Differential diagnosis of T2 hyperintense spinal cord lesions: Part B

Hyperintense spinal cord signal on T2‐weighted images is seen in a wide‐ranging variety of spinal cord processes. Causes including simple MR artefacts, trauma, primary and secondary tumours, radiation myelitis and diastematomyelia were discussed in Part A. The topics discussed in Part B of this two part series include multiple sclerosis, subacute combined degeneration of the spinal cord, cord infarction, arteriovenous shunts, transverse myelitis, neurosarcoidosis, AIDS‐associated vacuolar myelopathy, and syringohydromyelia. Characterization of the abnormal areas of T2 signal as well as their appearance on other MR imaging sequences, when combined with clinical context and laboratory investigations, will often allow a unique diagnosis, or at least aid in narrowing the differential diagnosis. A wide range of instructive cases is discussed here, with review of the published reports focusing on pertinent MR features to aid in diagnosis.     

Magnetic resonance imaging of intracranial tumors: intra-patient comparison of gadoteridol and ferumoxytol

This study aims to compare gadoteridol with ferumoxytol for contrast-enhanced and perfusion-weighted (PW) MRI of intracranial tumors. The final analysis included 26 patients, who underwent 3 consecutive days of 3T MRI. Day 1 consisted of anatomical pre- and postcontrast images, and PW MRI was acquired using gadoteridol (0.1 mmol/kg). On Day 2, the same MRI sequences were obtained with ferumoxytol (510 mg) and on Day 3, the anatomical images were repeated to detect delayed ferumoxytol-induced signal changes. The T₁-weighted images were evaluated qualitatively and quantitatively for enhancement volume and signal intensity (SI) changes; PW data were used to estimate the relative cerebral blood volume (rCBV). All 26 lesions showed 24-hour T₁-weighted ferumoxytol enhancement; 16 also had T₂-weighted hypointensities. In 6 patients, ferumoxytol-induced signal changes were noted in areas with no gadoteridol enhancement. Significantly greater (P< .0001) SI changes were seen with gadoteridol, and qualitative analyses (lesion border delineation, internal morphology, contrast enhancement) also showed significant preferences (P= .0121; P = .0015; P < .0001, respectively) for this agent. There was no significant difference in lesion enhancement volumes between contrast materials. The ferumoxytol-rCBV values were significantly higher (P = .0016) compared with the gadoteridol-rCBV values. In conclusion, ferumoxytol provides important information about tumor biology that complements gadoteridol imaging. The rCBV measurements indicate areas of tumor undergoing rapid growth, whereas the 24-hour scans mark the presence of inflammatory cells. Both of these functions provide useful information about tumor response to treatment. We suggest that dynamic and anatomical imaging with ferumoxytol warrant further assessment in brain tumor therapy.     

Magnetic resonance imaging at 3.0 T for submandibular gland sparing radiotherapy

Purpose

Besides sparing the parotid gland, sparing the submandibular gland is considered to be important in preventing xerostomia in head-and-neck cancer patients. Delineation of the submandibular gland at CT, and even on T₁- and T₂-weighted MR images, is difficult, due to low contrast with the surrounding tissues. MR sialography might be used for delineation.

Methods and materials

Sixteen oropharyngeal cancer patients received a CT and MRI exam as part of the standard treatment imaging protocol. Patients were scanned in their five-point RT immobilization mask. The MRI exam included T₁- and T₂-weighted MRI scans and an MR sialography scan. Thirty submandibular glands were delineated on only CT, on the combined CT and T₁- and T₂-weighted MRI scans and on all MR images. A Wilcoxon signed-rank test was performed to test if the delineated volumes were significantly different.

Results

The delineated volume of the submandibular gland was 7.3 mL in the CT-delineation, 7.1 mL in the CT/MRI-delineation and 8.1 mL in the MRI-delineation. The MRI-delineation was significantly larger than the other delineations (p < 0.001). The differences were mainly located in the cranial direction.

Conclusion

The delineation of the submandibular gland was improved in the cranial direction by using T₁- and T₂-weighted MRI and MR sialography, compared to the other delineations.     

Molecular imaging of mesothelioma by detection of manganese‐superoxide dismutase activity using manganese‐enhanced magnetic resonance imaging

Malignant mesothelioma (MM) is a fatal malignancy with a rapidly increasing incidence in industrialized countries because of the widespread use of asbestos in the past centuries. Early diagnosis of MM is critical for a better prognosis, but this is often difficult because of the lack of disease‐specific diagnostic imaging. Here, we report that manganese‐enhanced magnetic resonance imaging (MEMRI) represents a promising approach for a more selective mesothelioma imaging by monitoring a high‐level expression of manganese‐superoxide dismutase (Mn‐SOD), which is observed in many MM. We found that most human MM cells overexpressed Mn‐SOD protein compared with human mesothelial cells and that NCI‐H226 human MM cells highly expressed Mn‐SOD and augmented Mn accumulation when loaded with manganese chloride (MnCl₂). The cells showed marked T₁‐signal enhancement on in vitro MRI after incubation with MnCl₂ because of the T₁ shortening effect of Mn²⁺. H226 subcutaneous tumor was preferentially enhanced compared with a lung adenocarcinoma cell tumor and another human MM cell tumor in MnCl₂‐enhanced T₁‐weighted MR image (T₁WI), correlating with their respective Mn‐SOD expression levels. Moreover, in a more clinically relevant setting, H226 xenografted pleural tumor was markedly enhanced and readily detected by MEMRI using manganese dipyridoxyl diphosphate (MnDPDP), a clinically used contrast agent, as well as MnCl₂. Therefore, we propose that MEMRI can be a potentially powerful method for noninvasive detection of MM, with high spatial resolution and marked signal enhancement, by targeting Mn‐SOD.     

Chordoid meningioma arising in the pineal region: a case report

We report a rare case of chordoid meningioma arising in the pineal region, which presented in a 22-year-old woman. Her only complaint was headache, and neurological examination revealed no deficits. She had suffered from prolonged fever a few weeks earlier, and her hematological findings included hypochromic microcytic anemia and a high serum level of C-reactive protein (CRP). Cranial magnetic resonance (MR) images demonstrated a 25 × 30 mm mass in the pineal region, which showed iso-to low intensity on T₁-weighted images (T1WI), high to low intensity on T₂-weighted images (T2WI), and homogeneous enhancement with gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA). We performed subtotal removal of the tumor with an occipital transtentorial approach (OTA), and all her preoperative symptoms completely abated. Histological examination of this tumor specimen showed the typical pattern of chordoid meningioma. Chordoid meningioma has been known to correspond with Castleman’s disease, and pineal meningiomas are extremely rare among intracranial meningiomas. The details of this case are presented with a review of the literature.     

Differential diagnosis of T2 hyperintense spinal cord lesions: Part A

Hyperintense spinal cord signal on T2‐weighted images is seen in a wide‐ranging variety of spinal cord processes including; simple MR artefacts, congenital anomalies and most disease categories. Characterization of the abnormal areas of T2 signal as well as their appearance on other MR imaging sequences, when combined with clinical context and laboratory investigations, will often allow a unique diagnosis, or at least aid in narrowing the differential diagnosis. A wide range of instructive cases is discussed here with review of the published reports focusing on pertinent MR features to aid in diagnosis.     

Atypical diffusion‐weighted magnetic resonance findings in glioblastoma multiforme

The present report describes two patients with glioblastoma multiforme with the tumour demonstrating low central apparent diffusion coefficient values similar to those found in cerebral abscesses. Although conventional MR images were fairly specific for tumour, the cases illustrate the need for exercising caution when using diffusion‐weighted (DW) MR images for the differentiation of necrotic brain tumours from abscesses. The DW MR imaging information should always be integrated with the conventional spin‐echo MR images.     

A correlative study of CT, MR and pathology in rabbit liver after embolization by a China - Formulated lipiodol emulsion

Objective

To explore the MR characteristics following lipiodol retention in rabbit liver and to evaluate the sensitivity of CT (CT value >400 HU) and MR in displaying the hepatic degeneration and necrosis following embolization.

Methods

Thirty-two rabbits were randomly divided into 3 groups. In the control group (n=8), 2 ml of normal saline was injected into the right branch of the portal vein. In the first experimental group(n=12), 4 ml of lipiodol emulsion was injected into the main portal vein. In the second experimental group (n=12), 2 ml of lipiodol emulsion was injected into the right branch of the portal vein. CT and MR images were obtained before and after surgery in each group. The histopathologic condition was determined for all liver tissue specimens.

Results

In the control group, CT and MR did not show any significant changes in the livers after surgery. After the operations in the experimental groups, the regional CT attenuation was 601 ±101 HU in the largest slice, which had no abnormal signals on T₁WI and T₂WI. In the first group, histologic examinations showed there were concentrated lipiodol droplets around the portal areas. In the second group, serious degeneration and necrosis in the right hepatic lobe occurred in 9 rabbits. T₁WI displayed homogenous or non-homogenous low signals and T₂WI mainly displayed a high signal. However, these pathologic changes did not appear on CT scanning due to high attenuation of the lipiodol.

Conclusion

There were no remarkable hepatic changes on MR in rabbits following good retention of the formulated lipiodol emulsion mixture of lipiodol and urografin(CT value > 400 HU). MR displayed serious degeneration and necrosis of the liver following embolization.     

Preservation of tumour oxygen after hyperbaric oxygenation monitored by magnetic resonance imaging

Hyperbaric oxygen (HBO) has been proposed to reduce tumour hypoxia by increasing the dissolved molecular oxygen in tissue. Using a non-invasive magnetic resonance imaging (MRI) technique, we monitored the changes in MRI signal intensity after HBO exposure because dissolved paramagnetic molecular oxygen itself shortens the T1 relation time. SCCVII tumour cells transplanted in mice were used. The molecular oxygen-enhanced MR images were acquired using an inversion recovery-preparation fast low angle shot (IR-FLASH) sequence sensitizing the paramagnetic effects of molecular oxygen using a 4.7 tesla MR system. MR signal of muscles decreased rapidly and returned to the control level within 40 min after decompression, whereas that of tumours decreased gradually and remained at a high level 60 min after HBO exposure. In contrast, the signal from the tumours in the normobaric oxygen group showed no significant change. Our data suggested that MR signal changes of tumours and muscles represent an alternation of extravascular oxygenation. The preserving tumour oxygen concentration after HBO exposure may be important regarding adjuvant therapy for cancer patients.     

Pancreatic head melanoma producing obstructive jaundice: Magnetic resonance characteristics aiding differentiation from adenocarcinoma

A case is reported of malignant melanoma presenting as a mass in the head of the pancreas producing obstructive jaundice. On MR imaging the mass displayed signal characteristics not typical of adenocarcinoma but instead exhibited a low signal on T2‐weighted images and early phase dynamic enhancement, the combination of which should suggest the possibility of melanoma.     

Adhesive capsulitis: contrast-enhanced shoulder MRI findings

Purpose: Evaluation of contrast‐enhanced magnetic resonance imaging (CE‐MRI) findings in cases clinically diagnosed as adhesive capsulitis (AC). Methods: CE‐MRI images of 12 cases diagnosed as AC (13 shoulder joints) and nine control cases were retrospectively evaluated. AC diagnosis was established based on the history and clinical symptoms. MR signal intensity changes in the axillary pouch, rotator interval, biceps anchor and anterior–posterior capsules were analysed with regard to the presence of abnormal soft tissue and contrast enhancement. Capsular and synovial thickening were measured in the axillary recess and rotator interval on coronal oblique CE T1‐weighted images. Patient and control groups were compared by Fisher's exact and McNemar tests in terms of signal intensity changes and contrast enhancement in the described areas. Results: Comparison of the group with AC and the control group regarding intensity changes showed a statistically significant difference in the axillary pouch (P < 0.001). No significant difference was found in the rotator interval, biceps anchor and anterior–posterior capsules (P > 0.05). Comparison of AC and control groups in terms of contrast enhancement revealed statistically significant differences in the axillary pouch, rotator interval, biceps anchor and anterior–posterior capsules (P < 0.001). A significant difference was determined between the AC and control groups with regard to thickening in axillary pouch and rotator interval (P < 0.001). Conclusion: CE studies are useful for diagnosis of AC as it demonstrates thickening of specific soft‐tissue areas like joint capsule and synovium.     

A Prospective Evaluation of T2-Weighted First-Pass Perfusion MR Imaging In Diagnosing Breast Neoplasms

Objective To compare the results from breast cancer patients who undergo T2-weighted first-pass perfusion imaging after dynamic contrast-enhanced T1-weighted imaging during the same examination, and to evaluate if T2-weighted imaging can provide additional diagnostic information over that obtained with T1-weighted imaging. Methods Twenty-nine patients with breast lesions verified by pathology (benign 12, malignant 17.) underwent MR imaging with dynamic contrast-enhanced T1-weighted imaging of the entire breasts, immediately followed by 6-sections of T2-weighted first-pass perfusion imaging of the lesions. The diagnostic indices were acquired by individual 3D T1-weighted enhancement rate criterion and the T2 signalintensity loss rate criterion. The sensitivity and specificity were calculated and the 2 methods were compared. Results With the dynamic.contrast-enhanced T1-weighted imaging, there was a significant differences between the benign and malignant breast lesions (t =2.563,P=0.016). However we found a considerable overlap between the signal intensity increase in the carcinomas and that in the benign lesions, for a sensitivity of 94% and a specificity of 25%. With T2-weighted first-pass perfusion imaging, there was a very significant difference between the benign and malignant breast lesions(t =4.777,P< 0.001), and the overlap between the signal intensity decrease in the carcinomas and that of the benign lesions on the T2-weighted images was less pronounced than the overlap in the T1-weighted images, for a sensitivity of 88% and a specificity of 75%. Conclusion T2-weighted first-pass perfusion imaging may help differentiate between benign and malignant breast lesions with a higher level of specificity. The combination of T1-weighted and T2-weighted imaging is feasible in a single patient examination and may improve breast MR imaging.     

Susceptibility Weighted Imaging (SWI) of the kidney at 3 T – initial results

Susceptibility weighted imaging provides diagnostic information in strokes, hemorrhages, and cerebral tumors and has proven to be a valuable tool in imaging venous vessels in the cerebrum. The SWI principle is based on the weighting of T₂* weighted magnitude images with a phase mask, therewith improving image contrast of veins or neighbouring structures of different susceptibility, in general. T₂* weighted MRI is already used for assessment of kidney function. In this paper, the feasibility of SWI on kidneys was investigated. Translation of SWI from the brain to the kidneys comes along with two main challenges: (i) organ motion due to breathing and (ii) a higher oxygenation level of renal veins compared to the brain. To handle these problems, the acquisition time has been cut down to allow for breath-hold examinations, and different post-processing methods including a new phase mask were investigated to visualize renal veins. Results showed that by a new post-processing strategy SWI contrast was enhanced on average by a factor of 1.33 compared to the standard phase mask. In summary, initial experiences of SWI on the kidneys demonstrated the feasibility. However, further technical developments have to be performed to make this technology applicable in clinical abdominal MRI.