Magnetic resonance imaging contrast agents: theory and application to the central nervous system

Detection of pathological contrast enhancement with synthetic brain imaging from quantitative multiparametric MRI

BACKGROUND AND PURPOSE

We aimed to test whether synthetic T1-weighted imaging derived from a post-contrast Quantitative Transient-state Imaging (QTI) acquisition enabled revealing pathological contrast enhancement in intracranial lesions.

METHODS

The analysis included 141 patients who underwent a 3 Tesla-MRI brain exam with intravenous contrast media administration, with the post-contrast acquisition protocol comprising a three-dimensional fast spoiled gradient echo (FSPGR) sequence and a QTI acquisition. Synthetic T1-weighted images were generated from QTI-derived quantitative maps of relaxation times and proton density. Two neuroradiologists assessed synthetic and conventional post-contrast T1-weighted images for the presence and pattern of pathological contrast enhancement in intracranial lesions. Enhancement volumes were quantitatively compared.

RESULTS

Using conventional imaging as a reference, synthetic T1-weighted imaging was 93% sensitive in revealing the presence of contrast enhancing lesions. The agreement for the presence/absence of contrast enhancement was almost perfect both between readers (k = 1 for both conventional and synthetic imaging) and between sequences (k = 0.98 for both readers). In 91% of lesions, synthetic T1-weighted imaging showed the same pattern of contrast enhancement visible in conventional imaging. Differences in enhancement pattern in the remaining lesions can be due to the lower spatial resolution and the longer acquisition delay from contrast media administration of QTI compared to FSPGR. Overall, enhancement volumes appeared larger in synthetic imaging.

CONCLUSIONS

QTI-derived post-contrast synthetic T1-weighted imaging captures pathological contrast enhancement in most intracranial enhancing lesions. Further comparative studies employing quantitative imaging with higher spatial resolution is needed to support our data and explore possible future applications in clinical trials.

Unintentional direct intraventricular injection of gadolinium with fatal outcome: report of a case

Gadolinium diethylenetriamine penta-acetic acid (Gd-DTPA) is the main contrast agent used in MRI, known for its good tolerance and rare toxicity. Even intrathecal injection of limited doses of Gadolinium can be performed in some indications. To our knowledge, only 3cases of accidental intraventricular injection of Gadolinium have been yet reported in the literature. We report the case of a 40-year-old male patient, who presented with headaches and vomiting. Brain MRI showed a right parietal abscess. The patient underwent emergent surgery for drainage of the septic collection. Postoperative MRI showed the development of a hydrocephalus related to a ventriculitis. Another surgery was performed to set up an external ventricular shunt, which lead to an improvement of the neurological status. A control brain MRI was scheduled for the patient, which revealed extensive abnormal enhancement inside the right lateral ventricle, on the basal cisterns as well as a leptomeningeal enhancement. Shortly after Gadolinium injection, the patient presented a tonic-clonic seizure. This clinico-radiological context leads to discover of the inadvertent intraventricular administration. Afterward, the patient's condition quickly deteriorated. Two days after the MRI he presented a cardiorespiratory arrest followed by death. Direct administration of Gadolinium into a ventriculostomy mistaken for intravenous catheter is a rare but harmful situation. Despite their rarity, such cases prove the importance of tracing all lines to their insertion sites to be confident of their appropriateness for injection.

MR Imaging of Pituitary Region Lesions with Gadodiamide Injection

Twelve patients with known or suspected pituitary lesions underwent MR imaging with gadodiamide injection at a dose of 0.1 (n = 5) or 0.3 (n = 7) mM/kg. Six of the patients were also studied with 0.1 mM/kg gadopentetate dimeglumine. Consistent with previous reports gadodiamide injection was found to be a safe and effective contrast medium for MR imaging of the pituitary region. No additional diagnostic information was obtained using 0.3 mM/kg gadodiamide injection compared to 0.1 mM/kg gadopentetate dimeglumine in the same patients. The high dose (0.3 mM/kg) gadodiamide injection in 7 patients did not shorten the T2 value sufficiently to overwhelm the T1 shortening and leave pathologic lesions hypointense compared to precontrast studies. With the comparable relaxivities of gadodiamide injection and gadopentetate dimeglumine, similarities in results have to be expected when using these media for MR image enhancement.

Alternatives to GBCA: Are We There Yet?

Gadolinium has been widely used as the contrast agent of choice for magnetic resonance imaging (MRI). However, gadolinium administration is not always desired due to its inherent enhancement properties and potential side effects (nephrogenic systemic fibrosis). This article reviews gadolinium alternatives, iron-, and manganese- based agents, and their current clinical usage for contrast-enhanced MRI examinations.

Perilesional Inflammation in Neurocysticercosis - Relationship Between Contrast-Enhanced Magnetic Resonance Imaging, Evans Blue Staining and Histopathology in the Pig Model

Background

Disease manifestations in neurocysticercosis (NCC) are frequently due to inflammation of degenerating Taenia solium brain cysts. Exacerbated inflammation post anthelmintic treatment is associated with leakage of the blood brain barrier (BBB) using Evans blue (EB) staining. How well EB extravasation into the brain correlates with magnetic resonance imaging (MRI) using gadolinium (Gd) enhancement as a contrast agent and pericystic inflammation was analyzed in pigs harboring brain cysts of Taenia solium.

Methodology/Principal Findings

Three groups of 4 naturally infected pigs were assessed. The first and second groups were treated with both praziquantel plus albendazole and sacrificed two and five days post treatment, respectively. A third untreated group remained untreated. Pigs were injected with EB two hours prior to evaluation by Gd-enhanced T1-MRI, and euthanized. The EB staining for each cyst capsule was scored (EB grades were 0: 0%; 1: up to 50%; 2: over 50% but less than 100%; 3: 100%). Similarly, the Gd enhancement around each cyst was qualitatively and quantitatively scored from the MRI. The extent of pericystic inflammation on histology was scored in increasing severity as IS1, IS2, IS3 and IS4. Grade 3 EB staining and enhancement was only seen in treated capsules. Also, treated groups had higher Gd intensity than the untreated group. Grades of enhancement correlated significantly with Gd enhancement intensity. EB staining was correlated with Gd enhancement intensity and with IS4 in the treated groups. These correlations were stronger in internally located cysts compared to superficial cysts in treated groups.

Significance

EB staining and Gd enhancement strongly correlate. The intensity of enhancement determined by MRI is a good indication of the degree of inflammation. Similarly, EB staining highly correlates with the degree of inflammation and may be applied to study inflammation in the pig model of NCC.

Neurocysticercosis (NCC) is a frequent parasitic infection of the human brain in developing countries. The symptomatology of human NCC after antiparasitic treatment is generally related to inflammation. The presence and degree of enhancement after intravascular injection of the contrast agent gadolinium in magnetic resonance imaging (MRI) is commonly considered an evidence of blood brain barrier (BBB) leakage. Experimentally, the presence and degree of extravasation of Evans blue (EB) after intravascular injection into the tissues of the brain is a direct measure of blood brain barrier leakage. The BBB leakage of gadolinium in neurocysticercosis is commonly used as an indirect measure of inflammation but has never been experimentally proven. Here we evaluated the relationship between contrast T1-MRI, EB staining and histology findings in naturally infected pigs. There was a strong correlation between EB staining, contrast MRI and histopathology findings after antiparasitic treatment. This correlation was stronger when cysts were internally located in the brain than in superficial cysts partly located in the subarachnoid space (meninges). Contrast-enhanced MRI is a non invasive tool used in diagnosis and follow up of NCC patients. This study shows that the use of EB staining allows for the same conclusions as when using MRI post-treatment, and that both techniques correlate with histopathology findings. These results support the use of EB staining to study NCC using the porcine model as well as validate MRI enhancement to assess brain inflammation in patients.

Complex imaging features of accidental cerebral intraventricular gadolinium administration

Gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) is a contrast agent commonly used for enhancing MRI. In this paper, the authors report on 2 cases of postoperative inadvertent administration of Gd-DTPA directly into a ventriculostomy tubing side port that was mistaken for intravenous tubing. Both cases demonstrated a low signal on MRI throughout the ventricular system and dependent portions of the subarachnoid spaces, which was originally believed to be CSF with areas of T1 shortening in the nondependent portions of the subarachnoid spaces, and misinterpreted as basal leptomeningeal enhancement and meningitis. The authors propose that the appearance of profound T1 hypointensity within the ventricles and diffuse susceptibility artifact along the ependyma is pathognomonic of intraventricular Gd-DTPA and should be recognized.

Evaluating changes in radiation treatment volumes from post-operative to same-day planning MRI in High-grade gliomas

Background

Adjuvant radiation therapy (RT) with temozolomide (TMZ) is standard of care for high grade gliomas (HGG) patients. RT is commonly started 3 to 5 weeks after surgery. The deformation of the tumor bed and brain from surgery to RT is poorly studied. This study examined the magnitude of volume change in the postoperative tumor bed and the potential impact of RT planning.

Method and materials

This study includes 24 patients with HGG who underwent craniotomy and adjuvant RT with TMZ at our institution. All patients had immediate postoperative MRI and repeat MRI during the day of RT simulation. Gross tumor volumes (GTV), clinical target volumes (CTV) of initial 46 Gy (CTV1) and boost to 60 Gy (CTV2) were contoured on both sets of MRIs according to RTOG (Radiation Therapy Oncology Group) guidelines. For patients who recurred after RT, the recurrence pattern was evaluated.

Results

An average of 17 days elapsed between immediate and delayed MRIs. GTV1 (FLAIR abnormality and tumor bed) decreased significantly on the delayed MRI as compared to immediate post-operative MRI (mean = 30.96cc, p = 0.0005), while GTV2 (contrast-enhanced T1 abnormality and tumor bed) underwent a non-significant increase (mean = 6.82cc, p = 0.07). Such changes lead to significant decrease of CTV1 (mean decrease is 113.9cc, p<0.01), and significant increase of CTV2 (mean increase is 32.5cc, p=0.05). At a median follow-up of 13 months, 16 patients (67%) progressed, recurred, or died, with a progression-free survival time of 13.7 months. Twelve patients failed within all CTVs based on immediate and delayed MRIs, while one patient recurred outside of CTV2 based on immediate post-operative MRI, but within the CTV2 defined on delayed MRI.

Conclusion

The postoperative tumor bed of HGGs undergoes substantial volumetric changes after surgery. Treatment planning based on delayed MRI significantly reduces the volume of treated brain tissue without local control detriment. The marked reduction of volume treated to 46 Gy based on delayed MRI scan, could result in increased sparing of organs at risk. There may be a small risk of inadequate radiation field design if radiation planning is based on immediate post-operative MRI.

Brain microvascular endothelial cell association and distribution of a 5 nm ceria engineered nanomaterial

Purpose:

Ceria engineered nanomaterials (ENMs) have current commercial applications and both neuroprotective and toxic effects. Our hypothesis is that ceria ENMs can associate with brain capillary cells and/or cross the blood–brain barrier.

Methods:

An aqueous dispersion of ∼5 nm ceria ENM was synthesized and characterized in house. Its uptake space in the Sprague Dawley rat brain was determined using the in situ brain perfusion technique at 15 and 20 mL/minute flow rates; 30, 100, and 500 μg/mL ceria perfused for 120 seconds at 20 mL/minute; and 30 μg/mL perfused for 20, 60, and 120 seconds at 20 mL/minute. The capillary depletion method and light and electron microscopy were used to determine its capillary cell and brain parenchymal association and localization.

Results:

The vascular space was not significantly affected by brain perfusion flow rate or ENM, demonstrating that this ceria ENM did not influence blood–brain barrier integrity. Cerium concentrations, determined by inductively coupled plasma mass spectrometry, were significantly higher in the choroid plexus than in eight brain regions in the 100 and 500 μg/mL ceria perfusion groups. Ceria uptake into the eight brain regions was similar after 120-second perfusion of 30, 100, and 500 μg ceria/mL. Ceria uptake space significantly increased in the eight brain regions and choroid plexus after 60 versus 20 seconds, and it was similar after 60 and 120 seconds. The capillary depletion method showed 99.4% ± 1.1% of the ceria ENM associated with the capillary fraction. Electron microscopy showed the ceria ENM located on the endothelial cell luminal surface.

Conclusion:

Ceria ENM association with brain capillary endothelial cells saturated between 20 and 60 seconds and ceria ENM brain uptake was not diffusion-mediated. During the 120-second ceria ENM perfusion, ceria ENM predominately associated with the surface of the brain capillary cells, providing the opportunity for its cell uptake or redistribution back into circulating blood.

Residual and recurrent acoustic neuroma in hearing preservation procedures: neuroradiologic and surgical findings

Magnetic resonance imaging with gadolinium DTPA is currently the most accurate method for detecting small intracanalicular yestibular schwannomas. This imaging modality is not nearly as clear in diagnosis of a small residual or recurrent neuroma after a hearing preservation procedure. This study looked for gadolinium-enhanced MRI images mimicking recurrent lesions in 104 consecutive cases of unilateral acoustic neuroma removed with a hearing preservation technique by the retrosigmoid transmeatal approach. A number of cases with enhancing MRI images in the internal anditory canal were reoperated, permitting the histologic examination of the enhancing tissue. Criteria for the MRI diagnosis of residual-recurrent acoustic neuroma are presented, along with the short-to mid-term rate of "residual-recurrent" tumor.

Nondysraphic pediatric intramedullary spinal cord lipomas: report of 5 cases

OBJECT

Intramedullary spinal cord lipomas not associated with dysraphism are infrequently reported. When present, they typically occur in children and have a predilection for the cervical and thoracic spinal cord. The authors review the presentation, treatment, and disease course in 5 pediatric patients, and compare the outcomes with previously reported cases.

METHODS

With institutional review board approval, a retrospective chart review was undertaken at Children's Hospital Los Angeles.

RESULTS

Four patients with intramedullary spinal cord lipomas and 1 patient with a lipoblastoma, none associated with dysraphism, were retrospectively reviewed. There were 2 boys and 3 girls ranging in age from 2 months to 4 years. Four patients underwent a laminectomy or laminoplasty with one or more subtotal resections. One patient initially underwent a decompressive laminoplasty without debulking. The median follow-up was 8 years (range 12 months-11 years). Two patients had regrowth of their lipoma, necessitating a second surgery in one patient and 3 debulking surgeries in the other. Postoperatively, 3 patients developed mild kyphosis, none significant enough to require orthopedic intervention. One patient underwent a stabilization procedure at the time of the initial laminectomy and tumor debulking. No patient received chemotherapy or radiation. At the most recent follow-up visit, patients demonstrated improved neurological function when compared with preoperative status.

CONCLUSIONS

In addition to a decompressive laminectomy, debulking of the lipoma provides the best long-term neurological outcome. Gross-total excision is not warranted and usually is not possible. Long-term follow-up is needed, and repeat debulking of the lipoma is indicated if there is an increase in tumor size due to hyperplasia of residual adipocytes, when tumor growth is associated with neurological deterioration.

Comparison of gadobenate dimeglumine (Gd-BOPTA) with gadopentetate dimeglumine (Gd-DTPA) for enhanced MR imaging of brain and spine tumours in children

BACKGROUND

Gadobenate dimeglumine (Gd-BOPTA) demonstrates superior enhancement of brain tumours in adult patients than Gd-DTPA.

OBJECTIVE

To determine whether Gd-BOPTA has advantages over Gd-DTPA for enhanced MR imaging of paediatric brain and spine tumours.

MATERIALS AND METHODS

Sixty-three subjects, aged 6 months to 16 years, who were enrolled in a prospective, fully blinded, randomized parallel-group phase III clinical trial, received 0.1 mmol/kg doses of either Gd-BOPTA (n=29) or Gd-DTPA (n=34). The MR images were acquired before and within 10 min of contrast agent injection. The primary objective was to compare the difference from pre-dose to post-dose lesion visualization between Gd-BOPTA and Gd-DTPA. Lesion visualization was determined as the sum of individual scores for three criteria of lesion morphological characteristics (lesion border delineation, internal morphology, and contrast enhancement), each assessed qualitatively using 4-point scales. Quantitative evaluation compared changes in lesion-to-background (LBR) and contrast-to-noise (CNR) ratios and per cent enhancement. Monitoring for adverse events and evaluation of vital signs and laboratory values was performed.

RESULTS

Pre-dose to post-dose changes in lesion visualization were significantly better for Gd-BOPTA for both lesion level (2.68+/-2.17 vs. 1.05+/-1.90, P=0.0106) and patient level (2.55+/-2.18 vs. 1.14+/-1.68, P=0.0079) comparisons. The mean pre-dose to post-dose change in CNR was greater for Gd-BOPTA (9.13+/-15.36) than Gd-DTPA (2.18+/-9.90), but the difference was only marginally significant (P=0.0779; 95% CI: -0.553, 14.454) because of wide variations of signal intensity between lesions. Similar findings were obtained for LBR and per cent enhancement. No differences between the agents were noted in terms of safety parameters.

CONCLUSIONS

At an equivalent dose Gd-BOPTA is significantly better than Gd-DTPA for visualization of enhancing CNS tumours in paediatric patients.

Early-postoperative magnetic resonance imaging in glial tumors: prediction of tumor regrowth and recurrence

OBJECTIVE

This study investigated the value of early-postoperative magnetic resonance (EPMR) imaging in the detection of residual glial tumor and investigated the role of EPMR for the prediction of tumor regrowth and recurrence.

METHODS AND MATERIALS

We retrospectively analyzed pre- and post-operative magnetic resonance imaging results from 50 adult patients who underwent surgical treatment for supratentorial glial tumor. There were glioblastoma multiforme in 25 patients, astrocytoma (grades II and III) in 11 patients, oligodendroglioma (grades II and III) in 9 patients, and oligoastrocytoma (grades II and III) in 5 patients. EPMR imaging was performed within 24 h after surgery. EPMR findings were compared with the neurosurgeon's intraoperative estimation of gross tumor removal. Patterns of contrast enhancement at the resection site, in residual and developing tumor tissue and blood at the resection site were evaluated on EPMR and in follow-up studies. 'Residual tumor' was defined as contrast enhancing mass at the operative site on EPMR. 'Regrowth' was defined as contrast enhancing mass detected on follow-up in the same location as the primary tumor. 'Recurrence' was defined as appearance of a mass lesion in the brain parenchyma distant from the resection bed during follow-up.

RESULTS

Nineteen patients showed no evidence of residual tumor, regrowth, or recurrence on EPMR or any of the later follow-up radiological examinations. EPMR identified 20 cases of residual tumor. Follow-up showed tumor regrowth in 10 patients, and tumor recurrence in 1 case. EPMR showed contrast enhancement of the resection bed in 45 of the 50 patients. Four of the 20 residual tumors showed a thick linear enhancement pattern, and the other 16 cases exhibited thick linear-nodular enhancement. No thin linear enhancement was observed in the residual tumor group. Nine of the 10-regrowth tumors showed a thick linear-nodular enhancement pattern, and one exhibited thin linear enhancement in EPMR. For predicting regrowth tumor EPMR sensitivity was 91%, specificity was 100%, positive predictive value 1; negative predictive value was 0.9375.

CONCLUSION

EPMR, depending on the surgical site enhancement pattern, is a valuable means of demonstrating residual tumors, and can be used to predict possible regrowth after surgery.

Effects of pCO(2) on the CSF turnover rate in T(1)-weighted magnetic resonance imaging

The cerebrospinal fluid (CSF) secretion of rat was monitored by longitudinal relaxation time-weighted magnetic resonance imaging (T(1)-weighted MRI) in combination with a ventricular injection of a T(1)-relaxation reagent: gadolinium-diethylene triamine-N,N,N',N",N"-pentaacetic acid (Gd-DTPA). A cannula was inserted in the left lateral ventricle, and 5 microl of 8.5 mM Gd-DTPA was injected as a CSF marker. Changes in the image intensity of the CSF were measured every 30 s, and the turnover rate of CSF (k) in the left lateral ventricle was obtained from the dilution of Gd-DTPA, based on the assumption of a single compartment model. In the control conditions, k was 0.158 +/- 0.009 min(-1) at an arterial blood CO(2) tension (pCO(2)) of 38.6 +/- 2.2 mmHg (n = 10), which corresponds to the CSF secretion rate of 3.6 microl min(-1). The k value was decreased (0.078 +/- 0.010 min(-1), n = 4) by a carbonic-anhydrase inhibitor (acetazolamide). The turnover rate was decreased by hypocapnia (0.094 +/- 0.019 min(-1), pCO(2) = 24.7 +/- 2.9 mmHg, n = 4), and it increased gradually and reached a plateau level as a result of hypercapnia (0.194 +/- 0.011 min(-1), pCO(2) = 104.5 +/- 7.1 mmHg, n = 10). These results suggested that CO(2) upregulates the secretion of CSF in the rat.

Neuroimaging contrast agents in ophthalmology

Magnetic resonance (MR) imaging and computed tomography (CT) are routinely performed with the use of contrast materials in the diagnosis of neuro-ophthalmologic disease. Iodinated agents are commonly used in CT scanning and femoral contrast arteriography, and gadolinium is used in MR imaging. While contrast materials contribute greatly to diagnostic accuracy, they may also be responsible for adverse effects, ranging in severity from mild discomfort to death. The most frequent and severe side effects are associated with ionic iodinated contrast agents, while the rate of adverse reactions is less with use of nonionic iodinated contrast agents. Side effects and adverse reactions to gadolinium are uncommon, but they do occur. In neuro-ophthalmologic diagnosis, MR imaging is generally preferred over CT scanning, partly because of its greater ability to delineate soft tissue intracranial structures, but also because of the relative safety of gadolinium as a contrast agent. Properties of contrast agents are discussed in the context of specific imaging techniques and tissues investigated. Types and severity of adverse effects as well as risk factors for incurring such effects are summarized.

Use of T(2)-weighted susceptibility contrast MRI for mapping the blood volume in the glioma-bearing rat brain

The aim of this work was to evaluate the potential of T(2)-weighted, steady-state susceptibility-enhanced contrast magnetic resonance imaging (MRI), to characterize brain tumor heterogeneity and tumor vascularization. In vivo T(2)-weighted MRI experiments were carried out on normal rats (n = 11) and rats bearing C6 glioma (n = 17), before and after the injection of a remanent superparamagnetic contrast agent. The DeltaR(2) variations of the transverse relaxation rate due to the injection of the contrast agent were used to generate relative cerebral blood volume (CBV) maps. Contrast enhancement of the tumor was shown to reflect tissue vascularization rather than leakage of the blood-brain barrier. The quantitative results clearly show the heterogeneity of tumor vascularization and reveal a high vessel density in the peripheral area (CBV(per) approximately 17.2 +/- 2.3 sec(-1)) and a low vessel density in the central area of the tumor (CBV(cen) approximately 2.5 +/- 0.5 sec(-1)). Magn Reson Med 42:754-761, 1999.

Postcontrast magnetic resonance imaging to predict progression of traumatic epidural and subdural hematomas in the acute stage

OBJECTIVE

We investigated the possibility of predicting the progression of traumatic epidural hematomas (EDHs) and subdural hematomas (SDHs), in the acute stage, by using postcontrast magnetic resonance imaging (MRI) with gadolinium-diethylenetriaminepentaacetic acid.

METHODS

From January 1990 through December 1996, 41 patients with 43 hematomas (21 EDHs and 22 SDHs) underwent postcontrast MRI within 24 hours after injury. T1-weighted MRI was performed by using the spin echo method, after the administration of 0.1 mmol/kg gadolinium-diethylenetriaminepentaacetic acid, immediately after computed tomographic scanning.

RESULTS

All of the enhanced hematomas were enlarged, whereas nonenhanced hematomas, except for two SDHs with bleeding tendencies, remained unchanged or decreased in volume. The prediction rates for enlargement with this method were 100% (21 of 21) for EDHs and 91.0% (20 of 22) for SDHs. The sensitivity of this test in predicting enlargement was 100% (15 of 15) for EDHs and 81.8% (9 of 11) for SDHs. The specificity was 100% for both types of hematomas. The enlargement rates for diffusely enhanced hematomas were statistically greater than those for nonenhanced hematomas. All of the patients with diffusely enhanced hematomas, which were found during surgery to exhibit active bleeding points, experienced consciousness deterioration.

CONCLUSION

We conclude that diffuse enhancement indicates extravasation from broken vessels that continue to bleed and that diffusely enhancing hematomas will be rapidly enlarged. We think that postcontrast MRI can be very useful for predicting the progression of acute EDHs and SDHs.

Automatic tumor segmentation using knowledge-based techniques

A system that automatically segments and labels glioblastoma-multiforme tumors in magnetic resonance images (MRI's) of the human brain is presented. The MRI's consist of T1-weighted, proton density, and T2-weighted feature images and are processed by a system which integrates knowledge-based (KB) techniques with multispectral analysis. Initial segmentation is performed by an unsupervised clustering algorithm. The segmented image, along with cluster centers for each class are provided to a rule-based expert system which extracts the intracranial region. Multispectral histogram analysis separates suspected tumor from the rest of the intracranial region, with region analysis used in performing the final tumor labeling. This system has been trained on three volume data sets and tested on thirteen unseen volume data sets acquired from a single MRI system. The KB tumor segmentation was compared with supervised, radiologist-labeled "ground truth" tumor volumes and supervised k-nearest neighbors tumor segmentations. The results of this system generally correspond well to ground truth, both on a per slice basis and more importantly in tracking total tumor volume during treatment over time.

MRI measurement of brain tumor response: comparison of visual metric and automatic segmentation

An automatic magnetic resonance imaging (MRI) multispectral segmentation method and a visual metric are compared for their effectiveness to measure tumor response to therapy. Automatic response measurements are important for multicenter clinical trials. A visual metric such as the product of the largest diameter and the largest perpendicular diameter of the tumor is a standard approach, and is currently used in the Radiation Treatment Oncology Group (RTOG) and the Eastern Cooperative Oncology Group (EGOG) clinical trials. In the standard approach, the tumor response is based on the percentage change in the visual metric and is categorized into cure, partial response, stable disease, or progression. Both visual and automatic methods are applied to six brain tumor cases (gliomas) of varying levels of segmentation difficulty. The analyzed data were serial multispectral MR images, collected using MR contrast enhancement. A fully automatic knowledge guided method (KG) was applied to the MRI multispectral data, while the visual metric was taken from the MRI films using the T1 gadolinium enhanced image, with repeat measurements done by two radiologists and two residents. Tumor measurements from both visual and automatic methods are compared to "ground truth," (GT) i.e., manually segmented tumor. The KG method was found to slightly overestimate tumor volume, but in a consistent manner, and the estimated tumor response compared very well to hand-drawn ground truth with a correlation coefficient of 0.96. In contrast, the visually estimated metric had a large variation between observers, particularly for difficult cases, where the tumor margins are not well delineated. The inter-observer variation for the measurement of the visual metric was only 16%, i.e., observers generally agreed on the lengths of the diameters. However, in 30% of the studied cases no consensus was found for the categorical tumor response measurement, indicating that the categories are very sensitive to variations in the diameter measurements. Moreover, the method failed to correctly identify the response in half of the cases. The data demonstrate that automatic 3D methods are clearly necessary for objective and clinically meaningful assessment of tumor volume in single or multicenter clinical trials.

Immediate postoperative CT contrast enhancement following surgery of cerebral tumoral lesions

PURPOSE

Our goal was to evaluate the immediate postoperative contrast enhancement behavior of cerebral lesions and to gain further information about contrast enhancement in patients under general anesthesia.

METHOD

In the early postoperative period, CT scans with the without contrast medium were performed in 46 patients. The time interval between surgery and postoperative CT imaging ranged from 1 to 7.5 h (mean 4 h). Nineteen patients were under general anesthesia during CT investigation.

RESULTS

In the early postoperative period, contrast medium leakage into the tumor resection cavity was noted In 14 patients (30%). Another phenomenon that was observed was the appearance of a strong demarcation and distinct contrast of gray against white matter in 24 patients (52%). This characteristic, global contrast enhancement of the cerebral cortex, occurred in 17 of 19 patients (89%) investigated under general anesthesia.

CONCLUSION

In immediate postoperative CT scans, contrast medium leakage due to extravasation of contrast medium into the tumor resection cavity can be detected early. Moreover, a global contrast enhancement of the cerebral cortex can be detected as a frequent pattern in patients investigated under general anesthesia.

Neuroimaging studies of postobliteration nidus changes in cerebral arteriovenous malformations treated by gamma knife radiosurgery

BACKGROUND

Following radiosurgical treatment, the majority of patients with arteriovenous malformations (AVMs) are periodically examined by means of computed tomography (CT) and magnetic resonance imaging (MRI) to assess the attainment of nidus obliterations, as well as adverse radiation effects in the surrounding brain. However, few neuroimaging studies of the long-term results following complete obliterations, confirmed by angiography, have been published to date.

METHODS

CT, MRI, magnetic resonance (MR) angiographic and angiographic images, obtained after angiographic confirmation of complete nidus obliteration, were reviewed in 11 AVM patients treated with gamma knife radiosurgery. The period between angiographic confirmation of nidus obliteration and these most recent examinations was 12-84 months (mean, 29 months).

RESULTS

In ten patients who were assessed by CT, the obliterated nidus was shown to be isodense (eight cases). A significant time-related decrease in contrast enhancement was observed within 1 to 2 postobliteration years (five/seven cases). Eight patients were evaluated by MRI. On T1-weighted imaging, the nidus was shown to be hypointense (six cases) or a mixture of hypointense and isointense areas (two cases). On T2-weighted imaging, nidus intensity varied more than than observed on T1-weighted imaging, and time-related intensity increases were observed (two/seven cases). No flow-signal void was demonstrated in any of these cases. In four of the seven cases, in which serial postobliteration follow-up MRI studies were conducted, significant gadolinium enhancement persisted 3 years or more after obliteration (maximum of 7 years). No vascular abnormalities were demonstrated in seven patients who were assessed by conventional angiography and/or MR angiography.

CONCLUSIONS

Radiosurgery-induced changes in a nidus may continue for several years after angiography has shown complete AVM obliteration.

Early postoperative magnetic resonance imaging following nonneoplastic cortical resection

Postcraniotomy residual tumor is often determined by magnetic resonance (MR) imaging. Magnetic resonance changes that occur in the postoperative setting must be defined to ensure both the optimum timing of postoperative image acquisition and the accurate assessment of images for residual tumor. Postoperative changes in nontumor parenchyma have previously been described for computerized tomography but not for MR imaging. In the present study, 11 patients without intracranial neoplastic disease (six females and five males with a median age of 36 years) submitted to MR imaging 17 to 28 hours after undergoing temporal lobectomies for epilepsy. Four of the operations were performed with the patients under general anesthesia and seven under local anesthesia. Postoperative MR images (T1-weighted, T1-weighted gadolinium enhanced, and T2-weighted) were reviewed. Extraaxial fluid, air, or blood was present in all cases. Enhancement of the resection bed parenchyma occurred in seven (64%) of 11 patients. In three of the remaining four patients, assessment of parenchymal enhancement was obscured by extraaxial fluid collections. Dural enhancement occurred adjacent to the resection site in all of the cases and remotely in 73%. Eight (73%) of 11 patients displayed enhancement of the pia-arachnoid of the ipsilateral cerebral convexity, two (18%) of the contralateral convexity, and four (36%) of the pia-arachnoid overlying the cerebellum. Contrary to previous reports, contrast enhancement of nonneoplastic human brain parenchyma can occur postoperatively within 17 hours. Benign parenchymal contrast enhancement is usually linear in appearance; nonneoplastic dural and leptomeningeal enhancement can occur both adjacent to and distant from the surgical site. Extraaxial fluid collections can hinder MR evaluation of the resection bed.

MRI segmentation: methods and applications

The current literature on MRI segmentation methods is reviewed. Particular emphasis is placed on the relative merits of single image versus multispectral segmentation, and supervised versus unsupervised segmentation methods. Image pre-processing and registration are discussed, as well as methods of validation. The application of MRI segmentation for tumor volume measurements during the course of therapy is presented here as an example, illustrating problems associated with inter- and intra-observer variations inherent to supervised methods.

MRI of intracranial germ cell tumours

We reviewed MRI findings in proven intracranial germ cell tumours in 22 cases, 12 of whom received Gd-DTPA. On T1-weighted images, the signal intensity of the tumour parenchyma was moderately low in 19 cases and isointense in 3; on T2-weighted images, it was high in all cases. Regions of different intensity thought to be cysts were found in 17 (77%): 7 of 12 patients with germinoma (58%) and in all other cases. Of the 13 patients with pineal lesions T1-weighted sagittal images showed the aqueduct to be obstructed in 5, stenotic in 7 and normal in 1. Strong contrast enhancement was observed in all 12 cases. Of the 14 patients with suprasellar lesions, 5 were found to have an intrasellar extension, and in 3 of these, the normal pituitary gland, which could be distinguished from the tumour, was displaced anteriorly. Ten patients (45%) had multiple lesions.

Magnetic resonance imaging of the normal and chronically injured adult rat spinal cord in vivo

We assessed the capacity of MRI to show and characterise the spinal cord (SC) in vivo in normal and chronically injured adult rats. In the chronically injured animals the SC was studied by MRI and histological examination. MRI was performed at 1.5 T, using gradient-echo and spin-echo (SE) sequences, the latter with and without gadolinium-DTPA (Gd-DTPA). Several positions were tried for good alignment and to diminish interference by respiratory movements. Images of the SC were obtained in sagittal, coronal, and axial planes. Normal SC was observed as a continuous intensity in both sequences, although contrast resolution was better using SE; it was not possible to differentiate the grey and white matter. Low signal was seen in the damaged area in chronically injured rats, which corresponded to cysts, trabeculae, mononuclear infiltrate, and fibroglial wall on histological examination. Gd-DTPA failed to enhance the SC in normal or chronically injured rats. It did, however, cause enhancement of the lesion after acute SC injury.

Management of metastatic brain tumors

BACKGROUND

Brain metastases are the most common neurological complication of systemic cancer. They represent a serious cause of morbidity and mortality and a significant challenge for neurosurgeons. They outnumber all other intracranial tumors combined and, with advances in technology and treatment of systemic cancer, are on the increase as cancer patients live longer.

METHODS

We have reviewed the major factors that influence the occurrences of metastases in the central nervous system: primary cancer, patient age and sex, clinical aspects of presentation, basic diagnostic modalities, diagnostic imaging (computed tomography and magnetic resonance imaging), and treatment considerations. In discussing these different aspects, we emphasize the efficacy of different treatment options, including recent information regarding multiple metastases that broadens the scope of surgical implications. The criteria we present are directed toward considerations made by general surgeons, as well as those made by neurosurgeons.

CONCLUSIONS

Although radiotherapy remains the main therapeutic modality, surgical excision has increasingly shown advantages in certain settings, as has stereotactic radiosurgery. Chemotherapy is less effective, but its advantages are reviewed, as are the implications of recurrent metastases.

Early postoperative magnetic resonance imaging after resection of malignant glioma: objective evaluation of residual tumor and its influence on regrowth and prognosis

In the vast majority of studies that address the role of surgery in the management of high-grade gliomas, the degree of tumor removal accomplished is solely based on the intraoperative perception of the neurosurgeon. Despite its fundamental importance for a comparison of different treatment modalities, little systematic effort has been made to evaluate the residual gross tumor by neuroimaging methods immediately after surgery. We report the results of a prospective study using contrast-enhanced computed tomography and magnetic resonance imaging (MRI) to monitor 60 patients after the resection of a high-grade glioma. In each case, the first scans were obtained between Days 1 and 5 after surgery, followed by serial imaging every 2 to 3 months, usually until the condition of the patient deteriorated severely or the patient died. Gadolinium-enhanced MRI proved to be extremely valuable for assessing gross residual tumor when performed during Days 1 to 3 after the resection of a preoperatively enhancing high-grade glioma. This timing avoided surgically induced contrast enhancement and minimized interpretative difficulties. In delineating residual tumor, MRI was vastly superior to computed tomography. About 80% of tumor "recurrences" emerged from definitely enhancing remnants, as revealed by early postoperative MRI. The neurosurgeon's estimation of gross tumor burden reduction could be shown to be much less accurate (by a factor of 3) than the postoperative assessment by modern neuroimaging. In our series, residual tumor enhancement was the most predictive prognostic factor of survival in patients with glioblastoma, followed by radiotherapy. Patients with a residual tumor postoperatively had a 6.595-times higher risk of death in comparison to patients without a residual tumor. Patients undergoing radiotherapy had a 0.258-times lower risk of death in comparison to patients who were not treated with radiation. Concerning survival, the prognostic significance of both variables surpassed age and performance.

Intradural parenchymal involvement in the spinal subarachnoid space associated with primary lung cancer

BACKGROUND

Intradural parenchymal involvement (IPI) in the spinal subarachnoid space associated with primary lung cancer is rare. A retrospective study was undertaken to investigate the clinical and pathologic features of IPI.

METHOD

A total of 1215 cases of primary lung cancer were studied at autopsy; the results were reviewed retrospectively.

RESULTS

Twenty (1.65%) of the cases revealed IPI in the spinal subarachnoid space. The histologic diagnoses were small cell carcinoma in ten cases, adenocarcinoma in eight cases, and squamous cell carcinoma in two cases. In 14 (70%) cases, the IPI was located between the lumbar and cauda equina of the spinal cord. However, no metastases were observed in the cervical spinal cord. Brain metastasis, vertebral metastasis, and meningeal carcinomatosis were seen in 70%, 60%, and 40% of the 20 cases, respectively, suggesting that these metastases may be related to the metastatic pathway to the spinal cord. Most patients had neurologic symptoms or signs referable to IPI; IPI could be diagnosed before death in only one patient by magnetic resonance imaging. The median interval between diagnosis of lung cancer and development of IPI and median survival after the onset of neurologic symptoms referable to IPI were 415 days and 110 days, respectively.

CONCLUSION

The authors retrospectively received 1215 autopsies of patients with primary lung cancer and found 20 (1.65%) with IPI.

Diffusion into rat brain of contrast and shift reagents for magnetic resonance imaging and spectroscopy

A sensitive radiotracer technique was used to measure transfer constants (Kis) for blood to brain diffusion of the MR contrast reagent gadolinium diethylenetriaminepentaacetate (GdDTPA2-) and the MR shift reagent dysprosium triethylenetetraminehexaacetate (DyTTHA3-) across the normal and the ischemically injured blood-brain barrier (BBB) of rats. In rats with a normal BBB mean Kis (nL/g/s) for these reagents ranged from 0.3 to 1.4 across eight brain regions and were significantly lower in each region than Kis for sucrose (1.5-3.2), a substance known to be a poor permeant of the intact BBB. Kis measured 6 h after a 10 min period of normothermic forebrain ischemia were increased to 4.0-6.2 (reagents) and 6.6-7.5 (sucrose) in two brain regions, striatum and hippocampus, known to be especially vulnerable to ischemic injury. Measurements of BBB permeability to DyTTHA3- after osmotic opening of the barrier with hypertonic arabinose gave Kis of 25-30 in forebrain regions. Estimates of reagent concentrations in brain interstitial fluid 30 min after dosing the animals indicated that both an extremely high dose of DyTTHA3- and severe disruption of the BBB would be required to shift the resonance frequency of extracellular Na+ appreciably. With the moderate degrees of BBB injury produced by short-term ischemia, a dose of GdDTPA2- about 25 times the usual clinical dose of 0.1 mmol/kg would be required to quantify the injury by dynamic MRI.

Intradural conus and cauda equina tumours: a retrospective review of presentation, diagnosis and early outcome

This is a retrospective review of the clinical presentation, diagnosis and management of 62 patients with histologically proven intradural conus and cauda equina tumours. In the majority of cases the clinical presentation clearly suggests the need for further investigation. One fifth of the patients had small intramedullary tumours, which presented particular diagnostic difficulty and required sophisticated cross sectional imaging.

NMR-contrast enhancement of experimental brain tumors with MnTPPS: qualitative evaluation by in vivo relaxometry

The applicability of the synthetic manganese porphyrin MnTPPS as tumor-selective MRI-contrast agent for brain tumors was investigated quantitatively by in vivo relaxometry. To exclude toxic effects of side products, the purification method for MnTPPS was improved. As a result, MnTPPS+Cl- (free acid) with a purity of more than 99.8% was obtained. For the in vivo quantification of the contrast effect the magnetization M(0) and the transversal relaxation time T2 were evaluated in different regions of rat brains with or without implanted gliomas and in temporal muscle. Measurements were performed before and after the application of MnTPPS. The ratio of the magnetization M(0) (TR = 3.5 sec) of the tissue under investigation and the contralateral striatum was defined as contrast ratio Rc(0). Without MnTPPS Rc(0) of edema (0.93 +/- 0.08) and tumor (0.91 +/- 0.07) did not differ from normal brain tissue (corpus callosum: 0.96 +/- 0.07; cortex: 0.98 +/- 0.05). T2 of edema (110 +/- 12 msec) and intracranial tumor (93 +/- 7 msec) were significantly longer than in normal tissue (corpus callosum: 73 +/- 8 msec; parietal cortex: 75 +/- 6 msec; striate nucleus: 78 +/- 7 msec, p < .01). Two hours after the injection of MnTPPS, magnetization of neoplastic tissue was selectively enhanced (TR = 3.5 sec), and T2 was reduced. The smallest dose of 0.06 mmol/kg body weight (bw) increased Rc(0) to 1.12 +/- 0.04, and 0.38 mmol/kg to 1.30 +/- 0.13 (p < .01). T2 of tumor decreased to 85 +/- 6 msec after 0.06 mmol/kg and to 65 +/- 6 msec after 0.38 mmol/kg bw.(ABSTRACT TRUNCATED AT 250 WORDS)

A quantitative assessment of the addition of MRI to CT-based, 3-D treatment planning of brain tumors

Quantitative 3-D volumetric comparisons were made of composite CT-MRI macroscopic and microscopic tumor and target volumes to their independently defined constituents. Volumetric comparisons were also made between volumes derived from coronal and axial MRI data sets, and between CT and MRI volumes redefined at a repeat session in comparison to their original definitions. The degree of 3-D dose coverage obtained from use of CT data only or MRI data only in terms of coverage of composite CT-MRI volumes was also analyzed. On average, MRI defined larger volumes as well as a greater share of composite CT-MRI volumes. On average, increases in block margin on the order of 0.5 cm would have ensured coverage of volumes derived from use of both imaging modalities had only MRI data been used. However, the degree of inter-observer variation in volume definition is on the order of the magnitude of differences in volume definition seen between the modalities, and the question of which imaging modality best describes tumor volumes remains unanswered until detailed histologic studies are performed. Given that tumor volumes independently apparent on CT and MRI have equal validity, composite CT-MRI input should be considered for planning to ensure precise dose coverage for conformal treatments.

Oblique sagittal magnetic resonance imaging visualizing vascular compression of the trigeminal or facial nerve

An oblique sagittal magnetic resonance (MR) imaging method was developed to provide better visualization of vascular compression of nerves. The MR images of 12 patients with trigeminal neuralgia and 24 with hemifacial spasm were analyzed. The oblique sagittal views were obtained along the nerve identified by the axial view at an angle of 105 degrees between the line along the dorsal brain stem and the line along the margin of the pontomedullary junction (in patients with hemifacial spasm) or by the midsagittal view through the midpons (in patients with trigeminal neuralgia). The T1- and T2-weighted, proton-density, and/or gradient-echo MR images were evaluated to optimize imaging conditions. The oblique sagittal gradient-echo MR image most clearly visualized vascular compression of the nerves as high-intensity lines in six patients with trigeminal neuralgia, which was confirmed intraoperatively in four. Fifteen (75%) of 20 oblique sagittal gradient-echo MR images demonstrated vascular compression of the facial nerves in patients with hemifacial spasm; 12 of these were confirmed intraoperatively. The control study used 15 oblique sagittal gradient-echo MR images of nonaffected contralateral and normal sites. Four false-positive findings were found. Oblique sagittal gradient-echo MR images are a useful planning aid, allowing differential diagnosis prior to microvascular decompression in trigeminal neuralgia and hemifacial spasm.

Cholesterol granuloma of the cerebello-pontine angle

An unusual case of cholesterol granuloma of the temporal bone is described presenting as a cerebellopontine tumor. This lesion seemed to arise from an inflammatory process obstructing pneumatized cells. It consists of extradural granulation tissue and must be distinguished from intradural epidermoid cyst, which is, instead, a dysembryogenetic neoplasm. Simple drainage of the granuloma was accomplished by posterior fossa approach, but the lesion recurred after a year. The diagnosis and surgical management of cholesterol granuloma are discussed.

Radiography, myelography, computed tomography, and magnetic resonance imaging of the spine

Various methods of documenting pathologic change in the spine and spinal cord are available to the veterinary practitioner. Intimidation caused by the imaging modality and the fear that one will not be able to recognize or diagnose a lesion are the factors that limit the use of diagnostic imaging. One needs only to be able to recognize the variations of normal anatomy to be successful. Once an abnormal area has been identified, the diagnosis is soon to follow. Therefore one should concentrate on improving the simple skills associated with image interpretation and normal anatomy. Lesion identification and definitive diagnoses will follow by natural progression.

Long-term results of radiosurgery for arteriovenous malformation: neurodiagnostic imaging and histological studies of angiographically confirmed nidus obliteration

Detailed follow-up results for 25 patients treated for cerebral arteriovenous malformation (AVM) with a gamma unit are presented. Complete nidus obliteration was angiographically confirmed in 16 (73%) of 22 cases receiving full-dose irradiation. There were no radiation- or AVM-related mortalities. However, we did experience one case of radiation-related morbidity and one of angiography-related mortality, the autopsy findings of which are discussed. Computed tomography scan and magnetic resonance imaging follow-up studies of radiosurgically treated AVMs indicated that increased enhancement of the nidus after contrast or gadolinium administration could persist even after obliteration of the AVM was angiographically confirmed.

The fate of tumour rests following removal of acoustic neuromas: an MRI Gd-DTPA study

The fate of capsular fragments left attached to vital structures at the time of otherwise total tumour removal was studied in 14 of 21 such patients who underwent acoustic neuroma surgery. Imaging using magnetic resonance Gd-DTPA at post-operative intervals of 6 months-12 years (mean 70 months) showed evidence of persistent tumour in half the patients. None of the patients had developed new symptoms and computed tomography had failed to demonstrate tumour recurrence. Persistence of the tumour was more likely if the residual fragments were not cauterized at the time of operation. Four of the seven persisting tumour rests showed evidence of gradual enlargement. The implications for patient management, particularly if an attempt is made to preserve hearing, are discussed.

Pitfalls of contrast-enhanced imaging in the nervous system

This brief review covers the evolving clinical role of paramagnetic contrast agents in magnetic resonance imaging of the central nervous system, with particular emphasis on potential pitfalls. The safety and efficacy of Gd-DTPA is now well-established. Approximately 35-40% of all scans performed in this country now utilize the agent. The major pitfalls center on overinterpretation of the characterization of disease by either enhancement or lack thereof in any particular process.