Postoperative evaluation for intracranial recurrence of medulloblastoma: MR findings with gadopentetate dimeglumine.

PURPOSETo characterize the gadopentetate dimeglumine-enhanced MR features of recurrent medulloblastoma.METHODSThe postsurgical gadopentetate dimeglumine-enhanced MR images of 48 patients (206 head examinations) with prior resection of medulloblastoma were retrospectively evaluated for enhancement in the brain parenchyma, meninges (dura, pia-arachnoid), and ventricles.RESULTSNineteen patients had recurrent tumor as determined by clinical course and positive imaging studies. Seventeen patients with recurrent disease had intracranial enhancement predominating in the pia-arachnoid (63%) or as a focal nodular brain lesion (26%). Three of these patients also had intraventricular metastases. None of the clinically healthy patients had these findings. One patient had recurrent tumor presenting within the fourth ventricle. Only 3 of 8 intraventricular lesions observed in the 4 patients initially enhanced with gadopentetate dimeglumine. Another patient with recurrent disease had extensive skeletal metastases without involvement of the central nervous system. Dural enhancement was observed in patients both with (42%) and without (38%) recurrent tumor.CONCLUSIONThe MR findings of pia-arachnoidal or focal nodular brain enhancement are highly specific in the diagnosis of recurrent medulloblastoma. Pia-arachnoidal or focal brain enhancement were also the most frequent patterns associated with recurrent tumor. Dural enhancement alone is not a reliable indicator of recurrent medulloblastoma. Not all intraventricular metastases enhance with gadopentetate dimeglumine, and careful evaluation for nonenhancing lesions within the ventricles should be made on postoperative MR examinations.     

The Central Bright Spot Sign: A Potential New MR Imaging Sign for the Early Diagnosis of Anterior Ischemic Optic Neuropathy due to Giant Cell Arteritis

BACKGROUND AND PURPOSE:A rapid identification of the etiology of anterior ischemic optic neuropathy is crucial because it determines therapeutic management. Our aim was to assess MR imaging to study the optic nerve head in patients referred with anterior ischemic optic neuropathy, due to either giant cell arteritis or the nonarteritic form of the disease, compared with healthy subjects.MATERIALS AND METHODS:Fifteen patients with giant cell arteritis–related anterior ischemic optic neuropathy and 15 patients with nonarteritic anterior ischemic optic neuropathy from 2 medical centers were prospectively included in our study between August 2015 and May 2016. Fifteen healthy subjects and patients had undergone contrast-enhanced, flow-compensated, 3D T1-weighted MR imaging. The bright spot sign was defined as optic nerve head enhancement with a 3-grade ranking system. Two radiologists and 1 ophthalmologist independently performed blinded evaluations of MR imaging sequences with this scale. Statistical analysis included interobserver agreement.RESULTS:MR imaging scores were significantly higher in patients with giant cell arteritis–related anterior ischemic optic neuropathy than in patients with nonarteritic anterior ischemic optic neuropathy (P ≤ .05). All patients with giant cell arteritis–related anterior ischemic optic neuropathy (15/15) and 7/15 patients with nonarteritic anterior ischemic optic neuropathy presented with the bright spot sign. No healthy subjects exhibited enhancement of the anterior part of the optic nerve. There was a significant relationship between the side of the bright spot and the side of the anterior ischemic optic neuropathy (P ≤ .001). Interreader agreement was good for observers (κ = 0.815).CONCLUSIONS:Here, we provide evidence of a new MR imaging sign that identifies the acute stage of giant cell arteritis–related anterior ischemic optic neuropathy; patients without this central bright spot sign always had a nonarteritic pathophysiology and therefore did not require emergency corticosteroid therapy.

Anterior ischemic optic neuropathy (AION) is the most common acute optic neuropathy in individuals older than 50 years of age, with an incidence of 2–10 per 100,000 people per year.^1,2 AION results from ischemic events within the optic nerve; these may be related to systemic vasculitis affecting large- and medium-caliber vessels in the arteritic form, due to giant cell arteritis (GCA-AION) or to blood flow disturbances associated with nonarteritic ischemic optic neuropathy (NA-AION). A rapid identification of the etiology is crucial because it determines the therapeutic management; corticosteroids must be promptly administered in cases of GCA-AION. Establishing the diagnosis of giant cell arteritis (GCA) may be challenging. The histopathologic result of a temporal artery biopsy has been considered the diagnostic standard but should not delay the prompt institution of steroid therapy. Some clinical signs suggest an arteritic etiology, including amaurosis fugax and systemic symptoms; a marked deterioration of visual acuity; more extensive visual field defects; diplopia; and the findings of fundus examination and fluorescein or indocyanine green angiography.³ However, ophthalmologists require a rapid diagnostic test to definitively rule out this diagnosis in an emergency setting. In GCA-AION, the granulomatous inflammatory artery infiltrate consists of T-lymphocytes, macrophages, and multinucleated giant cells. The pathogenesis is still not fully understood, though there have been major advances in recent years. Cytotoxic mediators and growth factors trigger the remodeling of the arterial wall, leading to ischemic manifestations by luminal stenosis.⁴An MR imaging examination is often used to narrow the differential diagnosis of optic disc edema and to highlight retrobulbar optic nerve enhancement in optic neuritis, a differential consideration of AION.^5,6 In addition, imaging of branches of the external carotid artery may be useful in the diagnosis of GCA.⁷ In contrast, radiologic data have traditionally failed to obtain positive signs for diagnosing AION; the most common finding in these patients is brain leukoaraiosis, particularly in patients with the nonarteritic form of the disease.⁸ MR imaging is the technique of choice for studying subtle ischemic events, either with contrast media or diffusion imaging. However, diffusion-weighted MR imaging is prone to distortion and motion artifacts, which may be problematic for the study of the anterior optic pathway.We raised the hypothesis that cytotoxic ischemia is more pronounced in GCA-AION compared with NA-AION, potentially leading to more permeable vessels in the former. We further hypothesized that damage to the anterior optic nerve microcirculation at the acute stage of AION might be revealed by contrast-enhanced MR imaging through a focal enhancement of the optic nerve head, the “central bright spot sign.”     

Rathke cleft cysts: correlation of enhanced MR and surgical findings.

PURPOSETo describe the gadolinium-enhanced MR findings of Rathke cleft cyst correlate them with the surgical findings, and define those preoperative findings that differentiate this lesion from other sellar and juxtasellar tumors.METHODSWe studied 18 patients who were diagnosed as having Rathke cleft cyst pathologically. These patients were imaged with T1- and T2-weighted coronal and sagittal spin-echo sequences. Fifteen of these patients received gadopentetate dimeglumine.RESULTSIn eight patients, the cyst showed low intensity on T1-weighted images and high intensity on T2-weighted images. At surgery, the cyst fluid was cerebrospinal fluid-like or light brown in five patients, motor oil-like in one patient, and milky in two patients. In 10 patients, cysts showed isointensity to high intensity on T1-weighted images and had various intensity on T2-weighted images. All 10 contained milky fluid. In three patients the intensity of fluid was heterogeneous. A waxy nodule was found in two patients. The position of the normal pituitary gland confirmed by surgery in all cases coincided with enhancement on MR imaging. The variable position of the normal pituitary gland was clearly identified in the sagittal images. The cyst walls showed no enhancement by gadopentetate dimeglumine.CONCLUSIONSBecause Rathke cleft cysts show variable intensities on MR, the diagnosis is often difficult when based on MR signal intensity values alone. MR imaging with gadopentetate dimeglumine does assist in the diagnosis of Rathke cleft cysts. Diagnostic clues include the lack of cyst wall enhancement and displacement of the normal pituitary gland.     

Radiation-induced optic neuropathy: characteristic appearances on gadolinium-enhanced MR.

PURPOSE: To assess the value of contrast-enhanced MR in the evaluation of radiation-induced optic neuropathy. MATERIALS AND METHODS: Three patients with rapid visual loss 1 1/2 to 3 years after radiation therapy to the optic nerves were studied with gadopentetate dimeglumine-enhanced MR images. All patients received over 5000 cGy, experienced rapid, permanent visual loss over several days to weeks, and underwent MR within weeks of presentation. RESULTS: Enhanced MR images on each patient revealed focal discrete enhancement of the intracranial optic nerve. One patient underwent biopsy of the enhancing segment; this revealed pathologic changes of radiation optic neuropathy. Optic nerve enhancement in a patient with visual loss and a prior history of radiation therapy to the orbits or optic nerves suggests radiation optic neuropathy. CONCLUSION: Contrast-enhanced MR of the orbits, optic nerves, and chiasm is the imaging test of choice in patients with vision loss after radiation therapy for sellar or skull base disease; MR findings may obviate the need for biopsy.     

Effects of gadopentetate dimeglumine administration after osmotic blood-brain barrier disruption: toxicity and MR imaging findings

Osmotic blood-brain barrier disruption with intraarterial chemotherapy has been shown to be beneficial in the treatment of malignant brain tumors. Imaging blood-brain barrier disruption is necessary to document the extent and degree of disruption and to correlate disruption with drug delivery. The present study evaluated blood-brain barrier disruption with gadopentetate dimeglumine-enhanced MR imaging and the associated toxicity of gadopentetate dimeglumine administration. Blood-brain barrier disruption was performed in seven dogs for imaging analysis and 17 dogs for toxicity evaluation. In the absence of gadopentetate dimeglumine administration, blood-brain barrier disruption could not be imaged. Enhanced MR imaging with a gadopentetate dimeglumine dose of 0.1 mmol/kg provided good images of disruption at an imaging time of 3 hr after disruption. However, when gadopentetate dimeglumine was given intravenously in conjunction with osmotic blood-brain barrier disruption, there was a statistically significant (p = .02) dose-dependent increase in the frequency of seizures, with 50% of the animals who received 0.1 mmol/kg and 75% who received 0.2 mmol/kg developing delayed seizures. Our findings show that, as with ionized iodinated CT contrast agents, gadopentetate dimeglumine is associated with toxicity when used in conjunction with osmotic blood-brain barrier disruption in dogs. Such toxicity may be a contraindication to the use of gadopentetate dimeglumine for monitoring patients with osmotically induced disruption of the blood-brain barrier.     

Contrast-enhanced MR imaging of optic nerve lesions in patients with acute optic neuritis

The purpose of this study was to determine if administration of gadopentetate dimeglumine aids in the MR detection of optic nerve lesions in patients with acute optic neuritis and to establish an efficient MR imaging protocol to effectively demonstrate such lesions. Patients with acutely decreased visual acuity were referred for MR imaging of the brain and orbits. Predominantly, T1-weighted images were obtained in axial and coronal planes with and without contrast administration. Enhancing lesions were observed in the optic nerve (7/14 patients) and optic chiasm (2/14), and associated white matter lesions were seen elsewhere in the brain (5/19). Our results indicate that administration of gadopentetate dimeglumine aids in the MR detection of lesions of the optic nerve and optic chiasm. Applicability of our MR imaging protocol was confirmed by the demonstration of these lesions and by the disseminated white matter lesions seen simultaneously elsewhere in the brain.     

Gadopentetate dimeglumine-enhanced MR of the brain: clinical utility and safety in patients younger than two years of age.

PURPOSETo evaluate the clinical utility and safety of gadopentetate dimeglumine as a contrast agent for MR of the brain in patients younger than 2 years of age.METHODSIn 125 consecutive patients younger than 2 years of age, MR images obtained before and after gadopentetate dimeglumine administration (0.1 mmol/kg) were independently and prospectively evaluated. After interpreting the unenhanced T1- and T2-weighted images, we rated the utility of contrast administration in each patient as not helpful, helpful, or essential for formulation of the radiologic diagnosis. Ratings were categorized both on the basis of the referring clinical diagnoses and on the basis of a radiologic diagnosis that was established from the clinical history and from the findings on the precontrast and postcontrast T1- and T2-weighted images. Patients'' vital signs were recorded, and general medical status was observed for 120 minutes after gadopentetate dimeglumine administration.RESULTSIn no case did gadopentetate dimeglumine permit detection of lesions when precontrast T1- and T2-weighted images were normal. In only 4 of 125 patients were postcontrast images considered essential for establishing the radiologic diagnosis. Abnormal contrast enhancement was radiologically helpful in 20 of 125 patients. Lack of enhancement was considered helpful in 22 of 125 patients. No adverse clinical events or clinically important trends in vital signs were observed after contrast administration.CONCLUSIONThe indiscriminate use of contrast agents in the MR imaging of patients younger than 2 years of age is not warranted. Appropriate decisions regarding the use of gadopentetate dimeglumine can be based on the findings in unenhanced T1- and T2-weighted images and on the referring clinical diagnosis.     

Enhancement of intervertebral disks with gadolinium complexes: comparison of an ionic and a nonionic medium in an animal model.

PURPOSETo compare MR contrast enhancement of intervertebral disk tissue after intravenous administration of equimolar doses of an ionic and of a nonionic gadolinium complex.METHODSContrast enhancement was measured on MR in lumbar intervertebral disks for 120 minutes after intravenous injection of gadoteridol or gadopentetate dimeglumine, 0.3 mmol/kg. MR studies were performed with each contrast medium in four rabbits. Contrast enhancement was measured in intervertebral disks as a function of time and contrast medium.RESULTSWith both contrast media, enhancement of normal intervertebral disks was detected. Enhancement of disks was significantly greater with gadoteridol than with gadopentetate dimeglumine.CONCLUSIONThe enhancement of cartilage is influenced by the molecular structure of the gadolinium complex. The negative charge of gadopentetate dimeglumine may give it a slower rate of diffusion into disk cartilage than a nonionic complex.     

Preoperative evaluation of osteosarcoma: value of gadopentetate dimeglumine-enhanced MR imaging.

Decisions regarding the surgical approach in osteosarcoma require accurate assessment of tumor extent. In order to determine whether enhancement with gadopentetate dimeglumine could add clinically significant information to that available with unenhanced MR imaging, 21 patients with osteosarcoma underwent preoperative MR imaging. T1- and T2-weighted spin-echo MR images obtained before and after administration of IV gadopentetate dimeglumine were evaluated to determine the conspicuity of marrow and soft-tissue extent of tumor, including tumor involvement of major neurovascular bundles and adjacent joints. MR results were correlated with tumor margins found at surgery. In some instances, use of gadopentetate dimeglumine obscured differentiation of tumor from normal marrow or tumor infiltration into perineurovascular fat, and tumor extension through pseudocapsule could not be differentiated from peritumoral edema after contrast administration. Contrast enhancement did assist in differentiation of intraarticular tumor from effusion; however, synovial invasion could be identified on unenhanced T1-weighted images by loss of synovial fat and cortical disruption. These results indicate that gadopentetate dimeglumine does not assist in defining tumor margins of osteosarcoma.     

Normal abdominal enhancement patterns with dynamic gadolinium-enhanced MR imaging

The objective of this study was to quantitatively and qualitatively determine contrast enhancement patterns of normal abdominal organs with dynamic gadolinium-enhanced magnetic resonance (MR) imaging. Dynamic gadolinium-enhanced, T1-weighted, spin-echo imaging was performed during a 23-second breath hold in 38 patients, with images acquired before, during, and at 1,2, and 5 minutes after bolus injection of gadopentetate dimeglumine. Enhancement patterns of normal liver, spleen, pancreas, adrenal gland, kidney, aorta, inferior vena cava, and fat were determined by visual evaluation and by performance of signal intensity measurements with an electronic cursor. Time-intensity curves demonstrated peak enhancement of all abdominal organs during or immediately after bolus injection of gadopentetate dimeglumine. MR enhancement patterns included visualization of renal cortical nephrogram and heterogeneous enhancement of the spleen during the bolus phase of contrast material administration. Peak enhancement of normal liver was 72%; spleen, 172%; pancreas, 82%; adrenal gland, 85%; and kidney, 291%. This study established reference data regarding abdominal organ enhancement that will be useful as dynamic gadolinium-enhanced MR imaging becomes clinically implemented.     

Administration of gadopentetate dimeglumine in MR imaging of intracranial tumors: dosage and field strength.

PURPOSE: To investigate the efficacy of 0.025, 0.05 and 0.1 mmol/kg gadopentetate dimeglumine in MR imaging of patients with intracranial tumors at mid and high field strength. METHODS: In 88 patients, an open-label phase III multicenter dose-finding study was performed at 0.5, 1.0, and 1.5 T MR units. Before and after (5, 15, 25 minutes) intravenous administration of gadopentetate dimeglumine, imaging was performed with T1-weighted spin-echo sequences. RESULTS: With 0.1 mmol/kg yielding the highest values, tumor enhancement and numerical tumor/brain contrast showed dose-dependent 5-minute postcontrast values (P less than 0.05). Compared to 5-minute postcontrast values, there was no significant change at 15 and 25 minutes. Although the lowest values of enhancement were found at 0.5 T, differences in enhancement among the field strengths were not statistically significant. The numerical data were confirmed by visual assessment of tumor/brain contrast. Eighty to 90% of cases had diagnostically valuable enhancement at 0.1 mmol/kg, 50% at 0.05 mmol/kg, and 10% at 0.025 mmol/kg (P less than 0.05). There were no adverse events. CONCLUSION: Our results confirm that 0.1 mmol/kg gadopentetate dimeglumine is more effective at enhancing intracranial tumors than lower doses at mid and high field MR units.     

The hypoglossal canal: normal MR enhancement pattern.

PURPOSETo review the anatomy of the hypoglossal canal and present the normal precontrast and postcontrast MR appearance of axial posterior fossa images.METHODSThirty-one axial MR examinations of the normal posterior fossa were retrospectively reviewed.RESULTSThe hypoglossal canals are well seen on 3-mm-thick axial MR images of the posterior fossa (28 [90%] of 31 patients). Symmetric intense intracanalicular enhancement after intravenous administration of gadopentetate dimeglumine is routine, typically with minor anterior extension into the nasopharyngeal region (28 [100%] of 28). A linear filling defect traversing the enhanced canal often is seen (21 [75%] of 28) and may represent hypoglossal nerve rootlets. Circumferential enhancement of the meninges at the level of the foramen magnum was a common finding (19 [64%] of 28).CONCLUSIONEnhancement within the hypoglossal canal with anterior extension beneath the skull base is a normal finding. This pattern is characteristic enough on MR imaging to aid interpretation of skull base lesions and to exclude the possibility of a mass within the hypoglossal canal.     

MR assessment of radiation-induced blood-brain barrier permeability changes in rat glioma model.

PURPOSETo assess the potential of a T1-weighted, gadolinium-enhanced MR technique for quantifying radiation-induced changes of blood-brain barrier permeability in a model of stereotactically implanted intracerebral gliomas in rats.METHODSWe calculated the gadolinium blood-to-tissue transport coefficient for gadopentetate dimeglumine from signal intensities in sequential MR images in nine control animals that were not irradiated and in five and three animals that had received 2500 cGy and 1500 cGy whole-brain irradiation, respectively, at 2 days before imaging.RESULTSThe average blood-to-tissue transport coefficient values were 9.76 mL.kg-1.min-1 in the control group, 23.41 mL.kg-1.min-1 in the 2500 cGy group, and 25.63 mL.kg-1.min-1 in the 1500-cGy group. Blood-to-tissue transport coefficients were significantly higher after irradiation, indicating increased radiation-induced blood-brain barrier permeability. Similar increased blood-brain barrier leakiness in brain tumors after high-dose irradiation has been shown by previous nuclear medicine studies using quantitative autoradiography.CONCLUSIONContrast-enhanced dynamic MR of brain gliomas is a sensitive method to document radiation-induced blood-brain barrier breakdown. Quantitative gadolinium-enhanced MR may become a useful tool for the management of patients with brain tumors undergoing radiation therapy.     

Gadopentetate dimeglumine as a bowel contrast agent: safety and efficacy

To determine the safety and efficacy of gadopentetate dimeglumine as a bowel contrast agent, magnetic resonance (MR) imaging (0.5 T) was performed with a formulation of gadopentetate dimeglumine (1.0 mmol/L of gadopentetate dimeglumine, 15 g/L of mannitol, 6-17 mL/kg) in 133 patients with intraabdominal mass lesions. Mostly short-lived gastrointestinal side effects were noted in 32% of patients. Gadopentetate dimeglumine provided uniform hyperintense marking of the bowel and contrast enhancement in the region of interest in 81% of patients. Among 78 patients with images obtained both before and after administration of contrast material, post-contrast improvement of lesion delineation was found in 62%. Among 55 patients with only postcontrast images, gadopentetate dimeglumine proved useful in 65%. Intravenous injection of scopolamine or glucagon effectively eliminated "ghost" images of the opacified bowel in 105 of 109 cases. The authors conclude that gadopentetate dimeglumine is a safe and effective bowel contrast agent for MR imaging.     

Benign lumbar arachnoiditis: MR imaging with gadopentetate dimeglumine

MR imaging was performed in 13 patients with benign lumbar arachnoiditis both before and after IV injection of gadopentetate dimeglumine. The arachnoiditis was proved by previous myelography in 12 patients and by noncontrast MR imaging in one patient. The disease was presumably the result of previous myelography and/or surgery. It was characterized as mild in two patients, moderate in two patients, and severe in nine patients. Imaging was performed on a 1.5-T unit, and both short and long TR images were obtained before and after contrast administration. Noncontrast MR images demonstrated changes consistent with arachnoiditis in all patients. After contrast, three patients had no enhancement, three patients had minimal enhancement, three patients had mild enhancement, and four patients had moderate enhancement. In no case did contrast enhancement alter the diagnosis or reveal additional findings that could not be seen on the noncontrast images. Gadopentetate dimeglumine enhancement plays little role in the diagnosis of lumbar arachnoiditis. If used for another reason, however, short TR scans may show enhancement of adherent roots in some cases. In addition, administration of gadopentetate dimeglumine will not cause sufficient enhancement to hinder the detection of arachnoiditis on long TR images and may aid in recognition of adherent roots on short TR images.     

Magnetic resonance enhancement pattern and diagnostic accuracy of gadofluorine M in a rabbit VX2 tumor model: Comparison with gadopentetate dimeglumine

Objective

The purpose of this study was to evaluate the enhancement pattern and the diagnostic accuracy of gadofluorine M in comparison with gadopentetate dimeglumine in a rabbit VX2 tumor model.

Materials and methods

Thirteen rabbits with experimentally induced VX2 carcinomas in the thighs underwent sequential T1-weighted enhancement MR imaging using a 3.0 T MR imager, first with gadopentetate dimeglumine, and then 24 (n = 4) or 4 h (n = 9) later with gadofluorine M. In 4 rabbits with 13 tumors, the time-percentage enhancement (PE; i.e., percentage of signal intensity increase) curve was obtained for up to 24 h for each contrast agent. In 9 rabbits with 49 tumors (random numbers of VX2 tumors were inoculated at random sites in the thigh), 3 readers unaware of the histopathologic results interpreted the MR images and determined the number and conspicuity level of the detected tumors. The reference standard was the histopathology of the specimen.

Results

The time-to-peak PE for gadopentetate dimeglumine was 1 min and gadopentetate dimeglumine showed a rapid washout pattern. The time-to-peak PE for gadofluorine M was 30 min and gadofluorine M showed a plateau enhancement pattern for up to 24 h. The peak PE of gadofluorine M was approximately twice that of the same dose of gadopentetate dimeglumine (108.2 ± 14.8 vs. 51.5 ± 24.0). The sensitivities for detecting VX2 tumors by 3 readers were 89.8% (44/49), 85.7% (42/49), and 95.9% (47/49) for gadopentetate dimeglumine-enhanced MR imaging, and 87.8% (43/49), 89.8% (44/49), and 89.8% (44/49) for gadofluorine M-enhanced MR imaging. No significant differences in the sensitivities existed between the two contrast agents for any reader. However, the conspicuity level of tumors was superior with gadofluorine M-enhanced MR imaging for two readers and similar for the other reader.

Conclusion

Gadofluorine M showed strong and plateau enhancement of tumors for up to 24 h. In the reader study, gadofluorine M showed better conspicuity for VX2 tumors than gadopentetate dimeglumine, but had a similar sensitivity.     

Benign lumbar arachnoiditis: MR imaging with gadopentetate dimeglumine

MR imaging was performed in 13 patients with benign lumbar arachnoiditis both before and after IV injection of gadopentetate dimeglumine. The arachnoiditis was proved by previous myelography in 12 patients and by noncontrast MR imaging in one patient. The disease was presumably the result of previous myelography and/or surgery. It was characterized as mild in two patients, moderate in two patients, and severe in nine patients. Imaging was performed on a 1.5-T unit, and both short and long TR images were obtained before and after contrast administration. Noncontrast MR images demonstrated changes consistent with arachnoiditis in all patients. After contrast, three patients had no enhancement, three patients had minimal enhancement, three patients had mild enhancement, and four patients had moderate enhancement. In no case did contrast enhancement alter the diagnosis or reveal additional findings that could not be seen on the noncontrast images. Gadopentetate dimeglumine enhancement plays little role in the diagnosis of lumbar arachnoiditis. If used for another reason, however, short TR scans may show enhancement of adherent roots in some cases. In addition, administration of gadopentetate dimeglumine will not cause sufficient enhancement to hinder the detection of arachnoiditis on long TR images and may aid in recognition of adherent roots on short TR images.     

Rectal carcinoma: Prospective comparison of conventional and gadopentetate dimeglumine enhanced fat-suppressed MR imaging

The purpose of this study is to compare the usefulness of conventional MR imaging and gadopentetate dimeglumine enhanced fat-suppressed MR imaging for the depiction and staging of rectal carcinoma. Thirty-two patients were prospectively evaluated by MR imaging using a 1.5-T unit. Based on the results of a barium study and/or digital examination, a balloon catheter was inserted to the level of the lesion before examination. Both conventional T1- and T2-weighted images and gadopentetate dimeglumine enhanced fat-suppressed T1-weighted images were obtained for all patients. The kappa statistics were performed for the evaluation of interobserver agreement and the McNemar test was performed for the analysis of staging accuracy. When only T1- and T2-weighted images were used, 5 of 32 tumors were not detected and the extent of 18 of 32 tumors were unclear. However, when gadopentetate dimeglumine enhanced fat-suppressed imaging was added, 24 of 32 tumors were well defined and only one tumor was not detected. In determining the depth of invasion, the staging accuracy was 72% for conventional imaging and 68% for all images combined. There was no significant difference between with gadopentetate dimeglumine fat-suppressed imaging and conventional imaging (P > .05). Use of gadopentetate dimeglumine (fat-suppressed imaging) resulted in overestimation of muscular invasion, peri-rectal fat invasion, and adjacent organ invasion in 12 patients, whereas nine patients were overestimated without the use of gadopentetate dimeglumine. In the detection of metastatic lymph nodes, gadopentetate dimeglumine enhanced fat-suppressed imaging also was not useful. Tumor detection was excellent using gadopentetate dimeglumine enhanced fat-suppressed images. However, the accuracy of staging was not improved by obtaining such images.     

Cortical hyperintensity on proton density-weighted images: An MR sign of cyclosporine-related encephalopathy.

PURPOSETo describe cortical hyperintensities in proton density-weighted images in six patients with presumed cyclosporine-induced neurotoxicity.METHODSIn six patients with clinical evidence of cyclosporine-related encephalopathy, MR imaging was performed after the onset of symptoms and signs (mean, 24 days after liver transplantation). Five of these patients had serial MR imaging for a period that varied from 2 to 20 months. Along with the imaging studies, the patients'' clinical status was evaluated and various laboratory parameters, including blood pressure and levels of cyclosporine, cholesterol, and magnesium, were monitored.RESULTSIn all six patients, initial MR studies showed hyperintensity of several cerebral gyri that was unequivocal only on proton density-weighted images. Although in five patients these signal abnormalities were limited to the cortex, one patient had increased signal in the subjacent white matter as well. In one patient, the images were also remarkable for areas of cortical hyperintensities on T1-weighted images. In another patient, cortical enhancement occurred after administration of gadopentetate dimeglumine, with a normal cortical signal on the precontrast images. The abnormal cortical signal began to fade after cyclosporine reduction, but in two patients it remained visible for at least 20 months. The neurologic symptomatology associated with cyclosporine-induced neurotoxicity included seizures (three patients), speech disorder (three patients), and disturbance of consciousness (three patients).CONCLUSIONCyclosporine-induced neurotoxicity occurring in patients after liver transplantation appears to affect the cerebral cortex preferentially. Because its MR equivalent resembles changes resulting from hypoxic injury or cortically centered vasculitis, we suspect the underlying mechanism may be a vascular injury that results in cortical hypoperfusion.     

Measurement of cerebral blood volume via the relaxing effect of low-dose gadopentetate dimeglumine during bolus transit.

PURPOSETo quantify regional cerebral blood volume (rCBV) on the basis of the enhancement of blood proton relaxation rates after intravenous administration of gadopentetate dimeglumine.METHODSA series of sequential MR images on one section was recorded during bolus transit with a standard fast low-angle shot sequence. The signal-intensity curves were converted into corresponding concentration-time curves from which rCBV images were calculated.RESULTSThe functional parameter images of rCBV were calculated pixel-by-pixel for two patients who had received a 1-second bolus injection of 1 mmol of gadopentetate dimeglumine. In a larger series of 62 patients, a mean blood volume of 4.6 +/- 1.6 vol% was determined for normal brain tissue.CONCLUSIONSThe relaxing effect of a contrast agent can be used to determine blood volume quantitatively. The results are in agreement with those obtained by nuclear medicine techniques. The proposed method requires no special hardware, and can thus be implemented on clinical MR scanners.