Perfusion abnormalities in congenital and neoplastic pulmonary disease: comparison of MR perfusion and multislice CT imaging

The aim of this work was to assess magnetic resonance (MR) perfusion patterns of chronic, non-embolic pulmonary diseases of congenital and neoplastic origin and to compare the findings with results obtained with pulmonary, contrast-enhanced multislice computed tomography (CT) imaging to prove that congenital and neoplastic pulmonary conditions require MR imaging over the pulmonary perfusion cycle to successfully and directly detect changes in lung perfusion patterns. Twenty-five patients underwent concurrent CT and MR evaluation of chronic pulmonary diseases of congenital (n=15) or neoplastic (n=10) origin. Analysis of MR perfusion and contrast-enhanced CT datasets was realized by defining pulmonary and vascular regions of interest in corresponding positions. MR perfusion calculated time-to-peak enhancement, maximal enhancement and the area under the perfusion curve. CT datasets provided pulmonary signal-to-noise ratio measurements. Vessel center-lines of bronchial arteries were determined. Underlying perfusion type, such as pulmonary arterial or systemic arterial supply, as well as regions with significant variations in perfusion were determined statistically. Analysis of the pulmonary perfusion pattern detected pulmonary arterial supply in 19 patients; six patients showed systemic arterial supply. In pulmonary arterial perfusion, MR and multislice CT imaging consistently detected the perfusion type and regions with altered perfusion patterns. In bronchial arterial supply, MR perfusion and CT imaging showed significant perfusion differences. Patients with bronchial arterial supply had bronchial arteries ranging from 2.0 to 3.6 mm compared with submillimeter diameters in pulmonary arterial perfusion. Dynamic MR imaging of congenital and neoplastic pulmonary conditions allowed characterization of the pulmonary perfusion type. CT imaging suggested the presence of systemic arterial perfusion by visualizing hypertrophied bronchial arteries.

Combined use of the intravascular blood-pool agent, gadomer, and carbon dioxide: A novel type of double-contrast magnetic resonance angiography (MRA)

PURPOSE

To evaluate the combined use of carbon dioxide (CO(2)) and a gadolinium-based blood-pool agent for magnetic resonance angiography (MRA).

MATERIALS AND METHODS

After an initial intravenous injection of the blood-pool agent Gadomer (Schering AG, Germany), repeated transcatheter CO(2) injections were performed in the aorta and the renal arteries of two fully-anesthetized pigs. Real-time images were acquired using a true fast imaging with steady-state precession (FISP) sequence.

RESULTS

During the CO(2) injections, the Gadomer-enhanced blood was totally replaced, resulting in an immediate, temporary, total signal loss in the vessel lumen. Susceptibility artifacts during the injections or catheter manipulations rarely occurred.

CONCLUSION

Due to T1-shortening, the circulating blood-pool agent prevents flow artifacts during catheter manipulations because the steady-state is reached much earlier. Therefore, this double-contrast MRA method improves catheter conspicuity and might be helpful for guiding and controlling intravascular procedures during interventional MRI.

Optimal design of k-space trajectories using a multi-objective genetic algorithm

Spiral, radial, and other nonrectilinear k-space trajectories are an area of active research in MRI due largely to their typically rapid acquisition times and benign artifact patterns. Trajectory design has commonly proceeded from a description of a simple shape to an investigation of its properties, because there is no general theory for the derivation of new trajectories with specific properties. Here such a generalized methodology is described. Specifically, a multi-objective genetic algorithm (GA) is used to design trajectories with beneficial flow and off-resonance properties. The algorithm converges to a well-defined optimal set with standard spiral trajectories on the rapid but low-quality end, and a new class of trajectories on the slower but high-quality end. The new trajectories all begin with nonzero gradient amplitude at the k-space origin, and curve gently outward relative to standard spirals. Improvements predicted in simulated imaging experiments were found to correlate well with improvements in actual experimental measures of image quality. The impact of deviations from the desired k-space trajectory is described, as is the impact of using different phantoms.

Functional Cardiac CT and MR

This study sought to validate different software applications for cardiac function analysis using ECG-gated CT and MR datasets in correlation with underlying heart rate. Ten patients and a set of ventricular phantoms underwent concurrent multislice-CT and cine-MR imaging for evaluation of cardiac function. Datasets from both imaging modalities were evaluated utilizing 2 volumetric analysis tools to determine left ventricular volume and mass. Initially, intraobserver measurement variability was assessed. Detected measurement variability was correlated with underlying absolute magnitude of cardiac volumes and masses. Subsequently, results were statistically evaluated by determining significant data variability depending on imaging modality and choice of evaluation software. Finally, the data variability was correlated with underlying heart rates. This study showed that all analyzed datasets uniformly presented intraobserver variations below 2%, and variability was not related to the magnitude of measurement. Significant measurement accuracy was proven in all calculated parameters obtained from the cardiac phantoms. Acquired patient datasets and calculated functional parameters showed significant data homogeneity, with measurement variability coefficients ranging from 0.935-0.955. CT datasets showed maximal data variability at heart rates below 60 BpM. MR datasets showed maximal data variability at heart rates above 90 BpM. In conclusion, CT and MR datasets allowed an interchangeable utilization of volumetric analysis tools. However, reliable volumetric analysis was limited to an optimal range of cardiac rates for each modality, thus emphasizing the necessity of reporting volumetric measurement results in combination with heart rate to allow for consideration of this possible cause for measurement variation.

Inter- and Intra-Observer Variability Assessment of in Vivo Carotid Plaque Burden Quantification Using Multi-Contrast Dark Blood MR Images

The chapter presents the research to test the hypotheses that (1) vessel wall volume measurements from dark blood MR images with multiple contrast-weightings (T1W, T2W and PDW) are highly reproducible, and that (2) the intra-observer and inter-observer variability of carotid wall volume measurements will be less than those obtained with maximum wall area (MaxWA) measurements.

METHODS

Sixteen patients (aged 72 +/- 7years) with carotid stenosis documented by duplex ultrasound were recruited for the study. Dark blood T1W, PDW and T2W MR images were used to measure carotid wall volume and MaxWA by two independent observers for inter-observer and intra-observer variability assessment.

RESULTS

The intra-observer absolute difference of carotid wall volume for T1W, T2W and PDW images were 67.3 +/- 47.5 mm(3) (2.3 +/- 1.8%), 63.2 +/- 52.2 mm(3) (2.0 +/- 1.3%), and 69.8 +/- 45.2 mm(3) (2.4 +/- 1.7%) respectively. The inter-observer absolute difference of carotid wall volume for T1W, T2W and PDW images were 103.5 +/- 141.8 mm(3) (3.0 +/- 3.1%), 95.9 +/- 102.1 mm(3) (3.1 +/- 2.6%), and 132.1 +/- 87.8 mm(3) (4.3 +/- 2.7%) respectively. The intra-observer absolute difference of carotid MaxWA for T1W, T2W and PDW images were 6.9 +/- 5.0 mm(2) (4.2 +/- 2.9%), 5.1 +/- 4.2 mm(2) (3.1 +/- 2.3%) and 7.5 +/- 4.7 mm(2) (4.2 +/- 2.7%) respectively. The inter-observer absolute difference of carotid MaxWA for T1W, T2W and PDW images were 9.5 +/- 4.2 mm(2) (5.8 +/- 2.3%), 6.4 +/- 6.1 mm(2) (3.8 +/- 3.1%) and 10.8 +/- 7.3 mm(2) (6.1 +/- 3.7%) respectively. Both intra- and inter-observer variability in carotid volume measurement tend to be smaller than that in carotid MaxWA measurement with intraclass correlation coefficients ranged 0.932 to 0.987 for volume measurement and 0.822 to 0.946 for MaxWA measurement.

Comparison of ECG?Gated Rectilinear vs. Real?Time Radial K?Space Sampling Schemes in Cine True?FISP Cardiac MRI

PURPOSE

To compare three k-space sampling schemes in cine True-FISP cardiac magnetic resonance imaging and to evaluate changes in calculated quantitative functional cardiac parameters as a function of underlying k-space sampling techniques.

MATERIAL AND METHODS

Using a 1.5 T MR imaging system (Magnetom Sonata, Siemens Medical Solutions, Erlangen, Germany), three k-space data-sampling schemes: rectilinear (2.96 ms/1.58 ms/70 degrees /12 s TR/TE/FA/AcquisitionTime), and two radial k-space acquisitions, with filtered back-projection (RADIAL) (2.45 ms/1.25 ms/ 50 degrees /3.3 s TR/TE/FA/AT), and steady-state projection imaging with dynamic echotrain readout (SPIDER) (3.39 ms/1.62 ms/55 degrees /1.8 s TR/TE/FA/AT) of a True-FISP sequence were applied in 10 healthy volunteers. Long- and short-axis breath-hold series were acquired and signal-to-noise ratios (SNR) for blood and myocardium were determined, as was contrast-to-noise ratios (CNR). Quantitative cardiac functional analysis included: determination of end-systolic/end-diastolic volumes, ejection fraction, and left ventricular mass. Functional analysis was performed by two independent readers three times for each volunteer and k-space sampling strategy. Statistical analysis evaluated the accuracy of the measurements obtained from each of the three sampling techniques and the intra- and interobserver reliability.

RESULTS

Intraobserver and interobserver reliability measures of functional data were homogeneous without statistically significant differences. Intraobserver correlation coefficients ranged from 0.94-0.99; interobserver correlation coefficients ranged from 0.97-0.99. Direct comparison of SPIDER- and RADIAL-sampled True-FISP sequences showed no statistically significant differences in measured functional parameters with interstudy correlation coefficients from 0.88-0.98. RADIAL and SPIDER images had better temporal resolution and were qualitatively judged to provide superior wall/blood border definition. Statistically significant differences were identified in each volumetric functional parameter when results from the rectilinear sampling acquisitions were compared with either radial or SPIDER sampling techniques. RADIAL and SPIDER results were consistently higher than volumetric measures obtained from the rectilinear data set.

CONCLUSION

Employing faster sampling schemes led to enhanced signal homogeneity while maintaining the necessary CNR for estimation of functional cardiac parameters. Enhanced signal homogeneity and maintained CNR will most likely improve the accuracy of the cardiac functional parameter determination.

Endolymphatic Duct Violation During Retrosigmoid Dissection of the Internal Auditory Canal: A Human Temporal Bone Radiographic Study

OBJECTIVE/HYPOTHESIS

Successful hearing preservation after acoustic neuroma resection is sometimes complicated by delayed hearing deterioration. The goal of this study was to investigate the hypothesis that internal auditory canal (IAC) drilling during retrosigmoid acoustic neuroma removal may result in endolymphatic duct (ELD) injury, a potential cause of delayed hearing loss (HL) after hearing preservation surgery.

STUDY DESIGN

Temporal bone anatomic and radiographic study and literature review.

METHODS

Twenty-one human temporal bones were analyzed with high-resolution multislice computed tomography (HRMCT) and subjected to standard retrosigmoid IAC dissection with labyrinthine preservation and follow-up HRMCT for analyses of the ELD. A MEDLINE search was performed of studies documenting long-term hearing preservation outcomes after retrosigmoid dissection.

RESULTS

Five of 21 (24%) bones were found to have violation of the ELD despite preservation of labyrinthine structures and the endolymphatic sac. These results correlate with the mean incidence of long-term hearing decline (26.6%). Reviews of human and animal studies indicate that injury to the ELD may create endolymphatic hydrops.

CONCLUSIONS

The ELD is vulnerable to injury during IAC dissection even if labyrinthine structures at the lateral aspect of the IAC are preserved. These findings may be helpful in explaining and potentially preventing some cases of long-term hearing deterioration that may be a result of endolymphatic hydrops after ELD injury during acoustic tumor removal. Careful preoperative review of imaging studies using HRMCT may prove useful before retrosigmoid dissection.

Low-Flow Vascular Malformations: MR-guided Percutaneous Sclerotherapy in Qualitative and Quantitative Assessment of Therapy and Outcome

PURPOSE

To prospectively assess the therapeutic procedure and outcome of magnetic resonance (MR)-guided percutaneous sclerotherapy in patients with low-flow vascular malformations.

MATERIALS AND METHODS

Seventy-six percutaneous sclerotherapy treatments were performed by one radiologist with real-time MR guidance in 15 patients (six female patients; mean age, 54.4 years +/- 11.1; nine male patients; mean age, 32.9 years +/- 14.1) with vascular malformations in the head and neck (n = 64), spine (n = 5), and extremities (n = 7). Qualitative assessment was used to analyze (a) individual success of therapy, (b) occurrence of complications, (c) time required for minimally invasive MR-guided sclerotherapy in regression analysis, (d) ability of MR imaging to depict postinterventional perfusion changes within the vascular malformation with calculation of changes in contrast-to-noise ratios, and (e) detection of volume changes at follow-up examinations with volumetric analysis.

RESULTS

Percutaneous sclerotherapy was performed successfully and without complications by filling targeted vascular malformations with sclerosing agent. Induced vascular sclerosis was used to successfully treat individual predominant symptoms, such as hemorrhage, pain, cosmetic disfigurement, and functional impairment. Quantitative analysis focusing on the actual interventional length of time presented an acceleration over the 5-year time period, matching a cubic function in regression curve fit and taking 31 minutes 50 seconds +/- 14 minutes. Induced vascular thrombosis was identified in all treated portions on postinterventional images by the statistically significant changes in contrast-to-noise ratio (P < .05) compared with preinterventional imaging. On follow-up images (ie, those obtained after 12 weeks +/- 6), shrinkage was observed in targeted portions (67.2% +/- 18.9).

CONCLUSION

MR imaging allows safe guidance and monitoring of minimally invasive sclerotherapy and permits verification of therapeutic success postinterventionally and during follow-up examinations.

Volumetric Assessment of Pulmonary Nodules with ECG-Gated MDCT

OBJECTIVE

The objective of our study was to assess physiologic lung deformation and compression originating from cardiovascular motion and their subsequent impact on determining the volume of small pulmonary nodules throughout the cardiac cycle on ECG-gated MDCT.

SUBJECTS AND METHODS

Seventy-three small noncalcified pulmonary nodules were identified in 30 patients who underwent ECG-gated MDCT. The volume of each nodule was assessed throughout the cardiac cycle using computer-aided automatic segmentation algorithms, and the assessment was repeated three times. To ensure the validity of the subtle changes in volume that were detected, we determined the volume and signal attenuation in phantom data sets and patient nodules without temporal or spatial differentiation. Subsequently, nodules were assigned to pulmonary segments, and volume changes were correlated to cardiac phases, nodular location, and mean nodular size. Statistical multivariate tests were performed to evaluate significant patterns.

RESULTS

The validity of significant measurements was proven in evaluated phantom data sets with a general tendency toward overestimating nodular volume (p = 0.492). Statistical evaluation of nodular signal attenuation confirmed true deformation and compression of nodules rather than partial volume effects as the reason for volume variations (p = 0.874). Differentiating pulmonary nodules in cardiac phases, pulmonary locations, and mean nodular volumes, we found that one single effect did not determine the amount of cardiovascular motion conveyed to pulmonary parenchyma and subsequently led to nodule deformation. Multivariate testing revealed statistically significant measures identifying patterns correlating variation in nodular volume with cardiac phase (p < 0.001), nodular location (p = 0.007), and mean nodular size (p < 0.001).

CONCLUSION

Cardiovascular motion was disproportionately conveyed to various pulmonary segments and led to changes in the volume of pulmonary nodules, especially in small pulmonary nodules. A precise volumetric assessment was therefore possible only by identifying the underlying cardiac phase.

Phase II clinical trial of interactive MR imaging-guided interstitial radiofrequency thermal ablation of primary kidney tumors: initial experience

PURPOSE

To perform a phase II clinical trial to evaluate efficacy and safety of interactive magnetic resonance (MR) imaging-guided radiofrequency (RF) interstitial thermal ablation (ITA) of primary renal tumors.

MATERIALS AND METHODS

Ten male patients (age range, 25-83 years) with peripheral renal cell carcinoma and contraindications to surgery were treated with percutaneous RF ITA entirely guided and monitored with a 0.2-T MR imaging unit. By using a 200-W RF ablation system and custom-fabricated MR imaging-compatible cool-tip electrodes, pulsed RF current was applied for single or multiple ablation cycle(s) of 12-15 minutes until the entire tumor was replaced by an enlarging zone of low signal intensity on T2-weighted and/or short inversion time inversion-recovery images acquired intermittently during the procedure. Kidney MR images were acquired before, immediately after, and 2 weeks after ablation and then every 3 months for 1 year and every 6 months thereafter. Intra- and postprocedural complications were assessed with clinical evaluation of patients for pain and hemodynamic instability and evaluation of MR images for evidence of hemorrhage or other unexpected findings. Follow-up images were assessed for delayed complications such as renal ischemia, infarct, urinoma, or tumor recurrence.

RESULTS

Treated tumors ranged between 0.63 and 16.90 mL in volume and 1.0 and 3.6 cm in maximum diameter. Successful RF electrode insertion and/or repositioning into the renal mass was achieved in all cases with direct MR "fluoroscopic" guidance. Thirty ablation cycles were conducted at 21 electrode positions in the 10 procedures, and complete ablation, as defined with MR imaging, was achieved in all cases by the end of the procedure. Apart from two small self-limited perirenal hematomas, no intra- or postprocedural complications were observed. No delayed complications or tumor recurrence occurred during a mean follow-up period of 25 months +/- 9.4 (standard deviation).

CONCLUSION

Although these results are preliminary, interactive MR imaging-guided RF ITA for treatment of primary renal tumors has a high success rate.

High-resolution MRI enhances identification of lesions amenable to surgical therapy in children with intractable epilepsy

PURPOSE

Many children with refractory epilepsy can achieve better seizure control with surgical therapy. An abnormality on magnetic resonance imaging (MRI), along with corroborating localization by other modalities, markedly increases chances of successful surgical outcome. We studied the impact of high-resolution MRI on the surgical outcome of intractable epilepsy.

METHODS

High-resolution MRI using four-coil phased surface array was obtained as part of the comprehensive presurgical protocol for children with focal onset intractable seizures evaluated by our epilepsy center during the first half of 2002.

RESULTS

Thirteen consecutive children, ages 5 to 18 years, entered this prospective study. For four patients with a lesion on a recent MRI examination with a standard head coil, management did not change with high-resolution MRI. Standard MRI in the other nine patients did not identify a lesion. However, high-resolution MRI with the phased-array surface coil found previously undiagnosed focal abnormalities in five of nine patients. These abnormalities included hippocampal dysplasia, hippocampal atrophy, and dual pathology with frontal cortical dysplasia. In four of nine patients, no identifiable lesion was identified on the high-resolution MRI. All patients underwent invasive monitoring. In three of five patients, newly diagnosed lesions correlated with EEG abnormalities, and resection was performed.

CONCLUSIONS

In our center, high-resolution MRI identified lesions not detected by standard MRI in more than half the children (56%). Technical advances such as four-coil phased surface array MRI can help identify and better delineate lesions, improving the diagnosis of patients who are candidates for surgical treatment of refractory epilepsy.

MRI-Guided Radiofrequency Thermal Ablation of Normal Lung Tissue: In Vivo Study in a Rabbit Model

OBJECTIVE

The purpose of this study was to assess the feasibility of MRI to guide and monitor radiofrequency ablation of normal pulmonary tissue in a rabbit model.

MATERIALS AND METHODS

Percutaneous puncture and lung radiofrequency ablation were performed in six New Zealand white rabbits under MRI control using a 0.2-T open MRI scanner. Technical feasibility and complication detection were evaluated. The ablation zone appearance and size were assessed using MRI, CT, and gross pathology. Interclass correlation coefficients (ICCs) of the maximum short-axis diameters of the lesions on gross pathology and the corresponding diameters as measured on each MRI pulse sequence and on CT scans were calculated.

RESULTS

MRI guidance of percutaneous puncture and radiofrequency ablation of pulmonary tissue is feasible. A pneumothorax was detected and treated using MRI. In the specimen, the mean coagulation necrosis diameter was 9.8 mm. The T1-weighted spoiled gradient-echo fast low-angle shot images showed the highest ICC (0.81) for the thermal lesion diameter.

CONCLUSION

Our results indicate that MRI guidance is feasible and useful for radiofrequency ablation of normal pulmonary tissue.

The Catheter-Driven MRI Scanner: A New Approach to Intravascular Catheter Tracking and Imaging-Parameter Adjustment for Interventional MRI

OBJECTIVE

Our aim was to test the feasibility of a hands-free approach to MRI that allows the interventionalist to track an angiographic catheter in real time throughout the procedure and to automatically change imaging parameters by catheter manipulation.

MATERIALS AND METHODS

A tracking method that is based on an active device localization was implemented on a 1.5-T MRI scanner. The system determines the current position and orientation of a catheter in 3D space in an endless feedback loop. Automatic scanning plane-adjustment procedures written in the software of the MRI system ensure image acquisition at the location of the catheter tip. The system calculates the device velocity to automatically adjust parameters such as field of view (FOV) and resolution. To evaluate the feasibility and performance in vivo and ex vivo, we performed experiments in two vessel phantoms and on six pigs.

RESULTS

The system collected the tracking data within 40 msec; an additional 10-20 msec was then required to perform the localization and velocity calculations and to update the image parameters. The system could localize a motionless catheter in the aorta in 100% and a moving catheter in 98% of measured attempts. The system responded in real time to changes in device velocity by dynamically adjusting spatial resolution and FOV in both phantom and porcine trials. Using this technique, we successfully catheterized the renal artery in two pigs.

CONCLUSION

Active tracking, combined with automatic scanning plane and imaging parameter adjustment, provides an intuitive MRI scanner interface for the guidance of the vascular procedure.

Multidetector CT angiography of arterial inflow and runoff in the lower extremities: a challenge in data acquisition and evaluation

PURPOSE

To show the feasibility of acquiring homogenous 3-dimensional datasets with high temporal and spatial resolution from computed tomographic angiographic (CTA) scans of the lower extremities and to assess automated vessel-tracking techniques for vascular evaluation.

METHODS

Eighteen men (mean age 67.0 years, range 43-83) with aneurysmal or occlusive vascular diseases underwent contrast-enhanced CTA of the lower limb arteries utilizing a 16-row CT imager. Curved multiplanar reformations were generated by manual selection of vessel centerlines in the infrarenal aorta and the arterial vasculature in the pelvis, thigh, and calf based on volume-rendering techniques. For each vessel, opacification and depiction were quantitatively evaluated. The manually segmented images were compared to datasets processed with automated vessel-tracking strategies by 5 radiologists, who evaluated diagnostic reliability and image quality. A Differential Receiver Operating Characteristic (DROC) analysis was performed.

RESULTS

An increase in the temporal and spatial resolution led to acquisition of high quality CTA datasets. Significant homogeneity of the vascular contrast-to-noise ratios was achieved in the pelvic (coefficient of variance 1.5% to 10.1%), thigh (0.1% to 9.4%), and calf (3.3% to 19.2%) vessels. The assessment of vascular delineation revealed full-width-at-half-maximum contrast values of 96.4%, 95.5%, and 111.3% in the pelvis, thigh, and calf, respectively. Observers were not able to distinguish between manual and automated vascular segmentation, as represented by a 0.56 value for the area under the DROC curve.

CONCLUSIONS

High-resolution CTA lower extremity datasets were acquired successfully, presenting vascular signal intensities of high homogeneity suitable for automated vessel-tracking techniques. Automated 3D visualization tools produced reliable, reproducible, and time-efficient centerline extractions that were comparable to manually defined centerlines.

Active device tracking and high-resolution intravascular MRI using a novel catheter-based, opposed-solenoid phased array coil

A novel two-element, catheter-based phased array coil was designed and built for both active MR device tracking and high-resolution vessel wall imaging. The device consists of two independent solenoid coils that are wound in opposite directions, connected to separate receive channels, and mounted collinearly on an angiographic catheter. The elements were used independently or together for tracking or imaging applications, respectively. The array's dual functionality was tested on a clinical 1.5 T MRI scanner in vitro, in vivo, and in situ. During real-time catheter tracking, each element gave rise to a high-amplitude peak in the respective projection data, which enabled reliable and robust device tracking as well as automated slice positioning. In vivo microimaging with 240 microm in-plane resolution was achieved in 9 s using the device and TrueFISP imaging. Therefore, a single device was successfully implemented that met the combined requirements of intravascular device tracking and imaging.

Assessment of parallel acquisition techniques in adrenal magnetic resonance imaging: does increased temporal resolution significantly improve visualization of adrenal lesions?

RATIONALE AND OBJECTIVES

To compare conventional radiofrequency coil reception techniques with parallel coil array acquisition methods in adrenal tissue visualization and to evaluate the dependence of temporal resolution on image quality in adrenal magnetic resonance magnetic resonance (MR) imaging.

MATERIAL AND METHODS

Using a 1.5 T MR imager, conventional and parallel sampled sequences were acquired in 10 healthy volunteers and 10 patients with adrenal lesions. The imaging protocol consisted of: conventional (TR/TE 4,730/125 ms; FA 150 degrees; NA 1; AT 25 s), and two parallel imaging SMASH techniques (TR/TE 4,090/125 ms; FA 150 degrees; NA 1 resulting in an AT of 12 s, as well as NA 2 resulting in an AT of 24 s) with generalized autocalibration T(2)-weighted turbo spin echo sequences with 5 mm slice thickness, 1.6 mm in-plane resolution, and an acceleration factor 2. Severity of breathing motion and aliasing artifact and overall image quality were rated on five-point scales and evaluated with student's t test; a differential receiver operating characteristic (DROC) analysis was performed.

RESULTS

Adrenal gland findings included adenomas, metastases, and hemorrhages. Acceleration of conventional turbo spin echo sequence with one signal average led to an increase in diagnostic power (DROC 0.362) as well as significant improvement in overall image quality (P(Volunteers) =.017; P(Patients) =.042) and reduction of breathing motion artifact in patients (P(Patients) =.012) while improving the temporal resolution. Parallel imaging with two signal averages resulted in further improvement of image quality over conventional imaging (DROC 0.303), (P(Volunteers) =.045; P(Patients) =.022), in the same acquisition time as the conventional method.

CONCLUSION

Parallel acceleration of sequences used for adrenal tissue visualization leads to a significant increase in diagnostic quality by significantly reducing breathing motion artifacts without sacrificing contrast indispensable for adrenal lesion characterization.

Suppression of prostate carcinogenesis by dietary supplementation of celecoxib in transgenic adenocarcinoma of the mouse prostate model

Epidemiological studies and clinical observations suggest that nonsteroidal anti-inflammatory drugs and certain selective cyclooxygenase (COX)-2 inhibitors may reduce the relative risk of clinically evident prostate cancer. This prompted us to investigate the chemopreventive potential of celecoxib, a selective COX-2 inhibitor, against prostate carcinogenesis in a transgenic adenocarcinoma of the mouse prostate (TRAMP) model. Similar to prostate cancer in humans, prostate malignancies in TRAMP mice progress from precursor intraepithelial lesions, to invasive carcinoma that metastasizes to lymph nodes, liver, lungs, and occasionally to bone. The basal enzyme activity and protein expression of COX-2 is significantly higher (>4-fold) in the dorsolateral prostate of TRAMP mice up to 24 weeks of age compared with their nontransgenic littermates. Eight-week-old TRAMP mice were randomly divided and fed either control diet (AIN 76A) or a custom prepared AIN 76A diet containing 1500-ppm celecoxib ad libitum for 24 weeks, a dosage that would compare with the normal recommended dose for the treatment of human disease. Studies from two independent experiments, each consisting of 10 mice on test, showed that the cumulative incidence of prostate cancer development at 32 weeks of age in animals fed with AIN 76A diet was 100% (20 of 20) as observed by tumor palpation, whereas 65% (13 of 20), 35% (7 of 20), and 20% (4 of 20) of the animals exhibited distant site metastases to lymph nodes, lungs, and liver. Celecoxib supplementation to TRAMP mice from 8-32 weeks of age exhibited significant reduction in tumor development (5 of 20) with no signs of metastasis. Celecoxib feeding resulted in a significant decrease in prostate (56%; P < 0.0003) and genitourinary weight (48%; P < 0.008). Sequential magnetic resonance imaging analysis of celecoxib-fed mice documented lower prostate volume compared with the AIN 76A-fed group. Histopathological examination of celecoxib-fed animals showed reduced proliferation, and down-modulation of COX-2 and prostaglandin E2 levels in the dorsolateral prostate and plasma, respectively. These results correlated with retention of antimetastasis markers, viz E-cadherin, and alpha- and beta-catenin, along with a significant decrease in vascular endothelial growth factor protein expression. Celecoxib supplementation also resulted in enhanced in vivo apoptosis in the prostate as monitored by several techniques including a recently perfected technique of 99mTc-labeled annexin V in live animals followed by phosphor imaging. One striking observation in an additional study was that celecoxib feeding to mice with established tumors (16 weeks of age) significantly improved their overall survival (P = 0.014), compared with AIN 76A-fed group. Our findings suggest that celecoxib may be useful in chemoprevention of prostate cancer.

Comparison of MR imaging sequences for liver and head and neck interventions

RATIONALE AND OBJECTIVES

To compare the appropriate pulse sequences for interventional device guidance during magnetic resonance (MR) imaging at 0.2 T and to evaluate the dependence of sequence selection on the anatomic region of the procedure.

MATERIALS AND METHODS

Using a C-arm 0.2 T system, four interventional MR sequences were applied in 23 liver cases and during MR-guided neck interventions in 13 patients. The imaging protocol consisted of: multislice turbo spin echo (TSE) T2w, sequential-slice fast imaging with steady precession (FISP), a time-reversed version of FISP (PSIF), and FISP with balanced gradients in all spatial directions (True-FISP) sequences. Vessel conspicuity was rated and contrast-to-noise ratio (CNR) was calculated for each sequence and a differential receiver operating characteristic was performed.

RESULTS

Liver findings were detected in 96% using the TSE sequence. PSIF, FISP, and True-FISP imaging showed lesions in 91%, 61%, and 65%, respectively. The TSE sequence offered the best CNR, followed by PSIF imaging. Differential receiver operating characteristic analysis also rated TSE and PSIF to be the superior sequences. Lesions in the head and neck were detected in all cases by TSE and FISP, in 92% using True-FISP, and in 84% using PSIF. True-FISP offered the best CNR, followed by TSE imaging. Vessels appeared bright on FISP and True-FISP imaging and dark on the other sequences.

CONCLUSION

In interventional MR imaging, no single sequence fits all purposes. Image guidance for interventional MR during liver procedures is best achieved by PSIF or TSE, whereas biopsies in the head and neck are best performed using FISP or True-FISP sequences.

Real-time catheter tracking and adaptive imaging

PURPOSE

To evaluate the performance of a real-time MR system for interventional procedures that adjusts specific image parameters in real time based on a catheter's speed of insertion.

MATERIALS AND METHODS

The system was implemented using only the hardware provided with a standard short-bore 1.5 T scanner (Siemens Magnetom Sonata) (with the exception of small tracking markers affixed to the catheter). The system tracks the position of an MR microcoil-instrumented catheter and automatically updates the scan plane's position and orientation, as well as other features, including, but not limited to, field of view, resolution, tip angle, and TE. A real-time feedback loop continuously localizes the tracking markers, updates the scan plane position and orientation, calculates the catheter's speed, adjusts the value of specific image parameters, then collects new image data, reconstructs an image, and provides it for immediate display. The system was evaluated in phantom and in vivo porcine experiments.

RESULTS

The system is able to accurately localize a moving catheter in the abdominal aorta, calculate the device speed, and respond by adjusting specified image parameters 98% of the time, with precision of approximately 2 mm and 1.5 degrees.

CONCLUSION

Simply slowing the speed of the catheter allows the clinician to adjust predetermined image parameters. This work also has the potential to build a degree of intelligence into the scanner, enabling it to react to changes in the clinical environment and automatically optimize specific image parameters.

Intraoperative MR imaging

Intraoperative MR imaging has become a safe and effective technology that has revolutionized the way neurosurgery is performed. Benefits include the ability to update data sets for navigational systems, to monitor tumor resections, to adjust the approach to intracranial lesions, and to guide functional and drug or cell delivery procedures. Use of this technique can help avoid inadvertent injury of important anatomic and vascular structures. In addition, complications such as ischemia or hemorrhage can be detected early. Intraoperative MR imaging is particularly useful for ensuring that brain biopsies yield diagnostic tissue and for assessing the completeness of tumor resection. As is true for any new technology, the benefits of intraoperative MR imaging must be examined carefully to guarantee appropriate use. Many neurosurgical procedures do not require real-time image guidance and can be performed safely using current surgical techniques, including microsurgical methods and frameless and frame-based stereotaxy. Other tumor resections, tumor biopsies, and surgical and interventional procedures distinctly benefit from the sophisticated information provided by intraoperative imaging techniques. In surgery for low-grade gliomas, intraoperative MR imaging has found general acceptance, whereas its usefulness to monitor the resection of high-grade gliomas remains controversial. The economic issues related to intraoperative MR imaging cannot be overlooked. The acquisition of an intraoperative MR imaging system is associated with considerable expense, and its performance increases the cost of equipment and the operating time. Despite these additional expenses, intraoperative MR imaging can lead to a potential overall cost reduction in the treatment of certain patients if long-term cure can be achieved, repeat resection can be avoided, or procedure-associated morbidity can be reduced. Although intraoperative MR imaging techniques hold tremendous potential, the definition of their appropriate role in the delivery of successful and cost-effective medical care awaits further study.

Assessment of Automatic Vessel Tracking Techniques in Preoperative Planning of Transluminal Aortic Stent Graft Implantation

OBJECTIVE

To evaluate automatic vessel tracking techniques in the course of preoperative planning prior to transluminal aortic endograft implantation by comparing accuracy, reproducibility, and postprocessing time with source image and volume-rendered analysis methods.

METHODS

Multislice computed tomography datasets of 5 patients with abdominal aortic aneurysms were preoperatively examined, performing volumetric analysis of diameter and position of renal artery orifices, aneurysmal neck, maximal aneurysmal extension, aortic bifurcation, and iliac arteries and bifurcation. Analysis was realized by utilizing transverse datasets, volume rendering, and automated vessel tracking strategies (MxView, Philips, Best, The Netherlands). Measurement techniques were evaluated by 2 independent readers 3 times for each patient and measurement modality. Statistical analysis evaluated accuracy of the measurements and intra- and interobserver reliability. Postprocessing time was documented.

RESULTS

Using transverse source datasets, intraobserver reliability ranged from 0.49 to 0.58. Intraobserver reliability improved to 0.7 to 0.98 when volume-rendered datasets were evaluated. Interobserver variability for transverse and volume-rendered datasets ranged from 0.49 to 0.76 and 0.70 to 0.96, respectively. Automated vessel tracking datasets did not demonstrate any intra- or interobserver variability. Based on transverse datasets, the length and diameter of iliac arteries and location and diameter of the aneurysmal neck were measured as statistically different in all cases in contrast to volume rendering and automated segmentation techniques. Postprocessing time consumption for measurements based on transverse, volume-rendered, and automated tracking segmentation datasets averaged 3.32 minutes, 25.43 minutes, and 2.24 minutes, respectively.

CONCLUSIONS

Preoperative measurements improve significantly if datasets are evaluated based on volume-rendering techniques. This time-consuming procedure can be shortened, while further reducing observer variability, with automatic segmentation techniques.

Percutaneous MR Imaging– guided Radiofrequency Interstitial Thermal Ablation of Tongue Base in Porcine Models: Implications for Obstructive Sleep Apnea Syndrome

PURPOSE

To test the feasibility and safety of a percutaneous magnetic resonance (MR) imaging-guided technique for radiofrequency (RF) interstitial thermal ablation of the tongue base and to correlate MR appearance of induced thermal lesions with histopathologic findings in pigs in acute and chronic porcine models.

MATERIALS AND METHODS

A 1-cm-tip RF electrode was inserted percutaneously into the tongue in 10 pigs with 0.2-T real-time MR guidance. The RF electrode was advanced up the midline between lingual arteries and stopped short of tongue mucosa. RF interstitial thermal ablation was performed at 90 degrees C +/- 2 and lasted 10 minutes. Postablation images were obtained with a 1.5-T MR imager. Five pigs were sacrificed immediately (acute model), while five were followed up for 1 month (chronic model) before they were sacrificed. MR-compatible fiducial coils were inserted into tongues with MR imaging guidance prior to RF ablation in the chronic group. Tongues were harvested for histopathologic analysis. Mean thermal lesion volume was compared with the Student t test on images obtained immediately, 2 weeks, and 1 month after RF ablation. Interclass correlation coefficients of lesion diameters at gross pathologic analysis and corresponding diameters with each pulse sequence were calculated.

RESULTS

Successful MR imaging-guided electrode positioning was achieved in all procedures without intra- or postprocedure complications because there was high vascular conspicuity and tissue contrast. Thermal lesions appeared hypointense with hyperintense surrounding rims with all sequences in both groups. At pathologic analysis, acute lesions appeared as pale necrotic areas surrounded by hyperemic rims, while chronic lesions demonstrated progressive circumferential fibrosis and significant volume shrinkage (P <.01). Thermal lesion diameters measured at gross pathologic analysis best agreed with corresponding diameters measured on short inversion time inversion-recovery images (interclass correlation coefficient = 0.85).

CONCLUSION

The results of this investigation demonstrate MR imaging-guided RF interstitial thermal ablation of the tongue base is feasible and safe and illustrate imaging and pathologic phenomena associated with creation and evolution of the induced thermal lesions.

Radiofrequency thermal ablation: Correlation of hyperacute MR lesion images with tissue response

PURPOSE

To investigate the hypothesis that the outer boundary of the hyperintense region observed in hyperacute (several minutes post-ablation) T2 and gadolinium contrast-enhanced (CE) T1-weighted magnetic resonance (MR) lesion images is an accurate predictor of eventual cell death from radiofrequency (RF) thermal ablation.

MATERIALS AND METHODS

A low-field, open MR imaging system was used to guide an ablation electrode into a thigh muscle of five rabbits and acquire in vivo T2 and CE T1-weighted MR volumes. Ablation occurred by applying RF current for two minutes with the electrode's temperature maintained at 90 degrees +/- 2 degrees C. After fixation, we sliced and photographed the tissue at 3 mm intervals, using a specially designed apparatus, to obtain a volume of tissue images. Digital images of hematoxylin and eosin (H&E) and Masson trichrome-stained histologic samples were obtained, and distinct regions of tissue damage were labeled using a video microscopy system. After the MR and histology images were aligned using a three-dimensional registration method, we compared tissue damage boundaries identified in histology with boundaries marked in MR images.

RESULTS

The lesions have distinct zones of tissue damage histologically: a central zone of necrotic cells surrounded by an outer zone with cells that appeared non-viable and associated with marked interstitial edema. In 14 histology images from five lesions, the inner and outer boundaries of the outer zone were compared with the boundaries of a hyperintense rim that surrounds a central hypointense region in the T2 and CE T1-weighted MR images. For T2 and CE T1-weighted MR images, respectively, the mean absolute distance was 1.04 +/- 0.30 mm (mean +/- SD) and 1.00 +/- 0.34 mm for the inner boundaries, and 0.96 +/- 0.34 mm and 0.94 +/- 0.44 mm for the outer boundaries. The mean absolute distances for T2 and CE T1-weighted MR images were not sufficiently different to achieve statistical significance (P = 0.745, 0.818, for the inner and outer boundary, respectively).

CONCLUSION

In hyperacute T2 and CE T1-weighted MR lesion images, observations strongly suggest that the outer boundary of the hyperintense rim corresponds to the region of eventual cell necrosis within a distance comparable to our ability to measure. This is good evidence that during RF ablation procedures, MR lesion images can be used to accurately localize the zone of irreversible tissue damage at the lesion margin.