Rapid freehand MR‐guided percutaneous needle interventions: An image‐based approach to improve workflow and feasibility

Purpose:

To develop and evaluate software‐based methods for improving the workflow of magnetic resonance (MR)‐guided percutaneous interventions.

Materials and Methods:

A set of methods was developed that allows the user to: 1) plan an entire procedure, 2) directly apply this plan to skin entry site localization without further imaging, and 3) place a needle under real‐time MR guidance with automatic alignment of three orthogonal slices along a planned trajectory with preference to the principal patient axes. To validate targeting accuracy and time, phantom experiments (96 targets) and in vivo paraspinal and kidney needle punctures in two pigs (55 targets) were performed. The influence of trajectory obliquity, level of experience, and organ motion on targeting accuracy and time was analyzed.

Results:

Mean targeting error was 1.8 ± 0.9 mm (in vitro) and 2.9 ± 1.0 mm (in vivo) in all directions. No statistically significant differences in targeting accuracy between single‐ and double‐oblique trajectories, novice and expert users, or paraspinal and kidney punctures were observed. The average time (in vivo) from trajectory planning to verification of accurate needle placement was 6 minutes.

Conclusion:

The developed methods allow for accurate needle placement along complex trajectories and are anticipated to reduce table time for MR‐guided percutaneous needle interventions. J. Magn. Reson. Imaging 2013;37:1202–1212. © 2013 Wiley Periodicals, Inc.     

Flexible add‐on solution for MR image‐guided interventions in a closed‐bore scanner environment

MRI is of great clinical utility for the guidance of various diagnostic and therapeutic procedures. In a standard closed‐bore scanner, the simplest approach is to manipulate the instrument outside the bore and move the patient into the bore for reference and control imaging only. Without navigational assistance, however, such an approach can be difficult, inaccurate, and time consuming. Therefore, an add‐on navigation solution is described that addresses these limitations. Patient registration is established by an automatic, robust, and fast (<30 sec) localization of table‐mounted MR reference markers and the instrument is tracked optically. Good hand‐eye coordination is provided by following the virtual instrument on MR images that are reconstructed in real time from the reference data. Needle displacements of 2.2 ± 0.6 mm and 3.9 ± 2.4 mm were determined in a phantom (P < 0.05), depending on whether the reference markers were placed at smaller (98‐139 mm) or larger (147‐188 mm) distances from the isocenter. Clinical functionality of the navigation concept is demonstrated by a double oblique, subscapular hook‐wire insertion in a patient with a body mass index of 30.1 kg/m². Ease of use, compactness, and flexibility of this technique suggest that it can be used for many other procedures in different body regions. More patient cases are needed to evaluate clinical performance and workflow. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Navigated MRI-guided liver biopsies in a closed-bore scanner: experience in 52 patients

Objectives

To evaluate clinical effectiveness and diagnostic efficiency of a navigation device for MR-guided biopsies of focal liver lesions in a closed-bore scanner.

Methods

In 52 patients, 55 biopsies were performed. An add-on MR navigation system with optical instrument tracking was used for image guidance and biopsy device insertion outside the bore. Fast control imaging allowed visualization of the true needle position at any time. The biopsy workflow and procedure duration were recorded. Histological analysis and clinical course/outcome were used to calculate sensitivity, specificity and diagnostic accuracy.

Results

Fifty-four of 55 liver biopsies were performed successfully with the system. No major and four minor complications occurred. Mean tumour size was 23?±?14 mm and the skin-to-target length ranged from 22 to 177 mm. In 39 cases, access path was double oblique. Sensitivity, specificity and diagnostic accuracy were 88 %, 100 % and 92 %, respectively. The mean procedure time was 51?±?12 min, whereas the puncture itself lasted 16?±?6 min. On average, four control scans were taken.

Conclusions

Using this navigation device, biopsies of poorly visible and difficult accessible liver lesions could be performed safely and reliably in a closed-bore MRI scanner. The system can be easily implemented in clinical routine workflow.

Key Points

? Targeted liver biopsies could be reliably performed in a closed-bore MRI. ? The navigation system allows for image guidance outside of the scanner bore. ? Assisted MRI-guided biopsies are helpful for focal lesions with a difficult access. ? Successful integration of the method in clinical workflow was shown. ? Subsequent system installation in an existing MRI environment is feasible.

     

MRI‐guided vacuum‐assisted breast biopsy: A phantom and patient evaluation of targeting accuracy

Purpose

To determine the spatial localization errors of magnetic resonance imaging (MRI)‐guided core biopsy for breast lesions using the handheld vacuum‐assisted core biopsy device in phantoms and patients.

Materials and Methods

Biopsies were done using a 10‐gauge handheld vacuum‐assisted core biopsy system (Vacora, Bard, AZ, USA) on a 1.5T MRI scanner (Philips Achieva, Best, The Netherlands). A standardized biopsy localization protocol was followed by trained operators for multiplanar planning of the biopsy on a separate workstation. Biopsy localization errors were determined as the distance from needle tip to center of the target in three dimensions.

Results

Twenty MRI‐guided biopsies of phantoms were performed by three different operators. The biopsy target mean size was 6.8 ± 0.6 mm. The overall mean three‐dimensional (3D) biopsy targeting error was 4.4 ± 2.9 mm. Thirty‐two MRI breast biopsies performed in 22 patients were reviewed. The lesion mean size was 10.5 ± 9.4 mm. The overall mean 3D localization error was 5.7 ± 3.0 mm. No significant differences between phantom and patients biopsy errors were found (P > 0.5).

Conclusion

MRI‐guided handheld vacuum‐assisted core biopsy device shows good targeting accuracy and should allow localization of lesions to within ～5 to 6 mm. J. Magn. Reson. Imaging 2009;30:424–429. © 2009 Wiley‐Liss, Inc.     

Transperineal prostate biopsy under magnetic resonance image guidance: a needle placement accuracy study

Purpose

To quantify needle placement accuracy of magnetic resonance image (MRI)‐guided core needle biopsy of the prostate.

Materials and Methods

A total of 10 biopsies were performed with 18‐gauge (G) core biopsy needle via a percutaneous transperineal approach. Needle placement error was assessed by comparing the coordinates of preplanned targets with the needle tip measured from the intraprocedural coherent gradient echo images. The source of these errors was subsequently investigated by measuring displacement caused by needle deflection and needle susceptibility artifact shift in controlled phantom studies. Needle placement error due to misalignment of the needle template guide was also evaluated.

Results

The mean and standard deviation (SD) of errors in targeted biopsies was 6.5 ± 3.5 mm. Phantom experiments showed significant placement error due to needle deflection with a needle with an asymmetrically beveled tip (3.2–8.7 mm depending on tissue type) but significantly smaller error with a symmetrical bevel (0.6–1.1 mm). Needle susceptibility artifacts observed a shift of 1.6 ± 0.4 mm from the true needle axis. Misalignment of the needle template guide contributed an error of 1.5 ± 0.3 mm.

Conclusion

Needle placement error was clinically significant in MRI‐guided biopsy for diagnosis of prostate cancer. Needle placement error due to needle deflection was the most significant cause of error, especially for needles with an asymmetrical bevel. J. Magn. Reson. Imaging 2007;26:688–694. © 2007 Wiley‐Liss, Inc.     

Intraprocedural diffusion‐weighted PROPELLER MRI to guide percutaneous biopsy needle placement within rabbit VX2 liver tumors

Purpose

To test the hypothesis that diffusion‐weighted (DW)‐PROPELLER (periodically rotated overlapping parallel lines with enhanced reconstruction) magnetic resonance imaging (MRI) can be used to guide biopsy needle placement during percutaneous interventional procedures to selectively target viable and necrotic tissues within VX2 rabbit liver tumors.

Materials and Methods

Our institutional Animal Care and Use Committee approved all experiments. In six rabbits implanted with 15 VX2 liver tumors, baseline DW‐PROPELLER images acquired prior to the interventional procedure were used for apparent diffusion coefficient (ADC) measurements. Next, intraprocedural DW‐PROPELLER scans were performed with needle position iteratively adjusted to target viable, necrotic, or intermediate border tissue regions. DW‐PROPELLER ADC measurements at the selected needle tip locations were compared with the percentage of tumor necrosis qualitatively assessed at histopathology.

Results

DW‐PROPELLER images demonstrated intratumoral tissue heterogeneity and clearly depicted the needle tip position within viable and necrotic tumor tissues. Mean ADC measurements within the region‐of‐interest encompassing the needle tip were highly correlated with histopathologic tumor necrotic tissue assessments.

Conclusion

DW‐PROPELLER is an effective method to selectively position the biopsy needle tip within viable and necrotic tumor tissues. The DW‐PROPELLER method may offer an important complementary tool for functional guidance during MR‐guided percutaneous procedures. J. Magn. Reson. Imaging 2009;30:366–373. © 2009 Wiley‐Liss, Inc.     

3.0‐T MR‐guided focused ultrasound for preoperative localization of nonpalpable breast lesions: An initial experimental ex vivo study

Purpose

To compare the accuracy of magnetic resonance‐guided focused ultrasound (MRgFUS) with MR‐guided needle‐wire placement (MRgNW) for the preoperative localization of nonpalpable breast lesions.

Materials and Methods

In this experimental ex vivo study, 15 turkey breasts were used. In each breast phantom an artificial nonpalpable “tumor” was created by injecting an aqueous gel containing gadolinium. MRgFUS (n = 7) was performed with the ExAblate 2000 system (InSightec). With MRgFUS the ablated tissue changes in color and increases in stiffness. A rim of palpable and visible ablations was created around the tumor to localize the tumor and facilitate excision. MRgNW (n = 8) was performed by MR‐guided placement of an MR‐compatible needle‐wire centrally in the tumor. After surgical excision of the tumor, MR images were used to evaluate tumor‐free margins (negative/positive), minimum tumor‐free margin (mm), and excised tissue volume (cm³).

Results

With MRgFUS localization no positive margins were found after excision (0%). With MRgNW two excision specimens (25%) had positive margins (P = 0.48). Mean minimum tumor‐free margin (±SD) with MRgFUS was significantly larger (5.5 ± 2.4 mm) than with MRgNW (0.9 ± 1.4 mm) (P < 0.001). Mean volume ± SD of excised tissue did not differ between MRgFUS and MRgNW localization, ie, 44.0 ± 9.4 cm³ and 39.5 ± 10.7 cm³ (P = 0.3).

Conclusion

The results of this experimental ex vivo study indicate that MRgFUS can potentially be used to localize nonpalpable breast lesions in vivo. J. Magn. Reson. Imaging 2009;30:884–889. © 2009 Wiley‐Liss, Inc.     

Registration of prostate histology images to ex vivo MR images via strand‐shaped fiducials

Purpose:

To present and evaluate a method for registration of whole‐mount prostate digital histology images to ex vivo magnetic resonance (MR) images.

Materials and Methods:

Nine radical prostatectomy specimens were marked with 10 strand‐shaped fiducial markers per specimen, imaged with T1‐ and T2‐weighted 3T MRI protocols, sliced at 4.4‐mm intervals, processed for whole‐mount histology, and the resulting histological sections (3–5 per specimen, 34 in total) were digitized. The correspondence between fiducial markers on histology and MR images yielded an initial registration, which was refined by a local optimization technique, yielding the least‐squares best‐fit affine transformation between corresponding fiducial points on histology and MR images. Accuracy was quantified as the postregistration 3D distance between landmarks (3–7 per section, 184 in total) on histology and MR images, and compared to a previous state‐of‐the‐art registration method.

Results:

The proposed method and previous method had mean (SD) target registration errors of 0.71 (0.38) mm and 1.21 (0.74) mm, respectively, requiring 3 and 11 hours of processing time, respectively.

Conclusion:

The proposed method registers digital histology to prostate MR images, yielding 70% reduced processing time and mean accuracy sufficient to achieve 85% overlap on histology and ex vivo MR images for a 0.2 cc spherical tumor. J. Magn. Reson. Imaging 2012; 36:1402–1412. © 2012 Wiley Periodicals, Inc.     

Fast‐spin‐echo imaging of inner fields‐of‐view with 2D‐selective RF excitations

Purpose:

To demonstrate the feasibility of two‐dimensional selective radio frequency (2DRF) excitations for fast‐spin‐echo imaging of inner fields‐of‐view (FOVs) in order to shorten acquisitions times, decrease RF energy deposition, and reduce image blurring.

Materials and Methods:

Fast‐spin‐echo images (in‐plane resolution 1.0 × 1.0 mm² or 0.5 × 1.0 mm²) of inner FOVs (40 mm, 16 mm oversampling) were obtained in phantoms and healthy volunteers on a 3 T whole‐body MR system using blipped‐planar 2DRF excitations.

Results:

Positioning the unwanted side excitations in the blind spot between the image section and the slice stack to measure yields minimum 2DRF pulse durations (about 6 msec) that are compatible with typical echo spacings of fast‐spin‐echo acquisitions. For the inner FOVs, the number of echoes and refocusing RF pulses is considerably reduced which compared to a full FOV (182 mm) reduces the RF energy deposition by about a factor of three and shortens the acquisition time, e.g., from 39 seconds to 12 seconds for a turbo factor of 15 or from 900 msec to 280 msec for a single‐shot acquisition, respectively. Furthermore, image blurring occurring for high turbo factors as in single‐shot acquisitions is considerably reduced yielding effectively higher in‐plane resolutions.

Conclusion:

Inner‐FOV acquisitions using 2DRF excitations may help to shorten acquisitions times, ameliorate image blurring, and reduce specific absorption rate (SAR) limitations of fast‐spin‐echo (FSE) imaging, in particular at higher static magnetic fields. J. Magn. Reson. Imaging 2010;31:1530–1537. © 2010 Wiley‐Liss, Inc.     

Reduced field‐of‐view single‐shot fast spin echo imaging using two‐dimensional spatially selective radiofrequency pulses

Purpose:

To demonstrate reduced field‐of‐view (RFOV) single‐shot fast spin echo (SS‐FSE) imaging based on the use of two‐dimensional spatially selective radiofrequency (2DRF) pulses.

Materials and Methods:

The 2DRF pulses were incorporated into an SS‐FSE sequence for RFOV imaging in both phantoms and the human brain on a 1.5 Tesla (T) whole‐body MR system with the aim of demonstrating improvements in terms of shorter scan time, reduced blurring, and higher spatial resolution compared with full FOV imaging.

Results:

For phantom studies, scan time gains of up to 4.2‐fold were achieved as compared to the full FOV imaging. For human studies, the spatial resolution was increased by a factor of 2.5 (from 1.7 mm/pixel to 0.69 mm/pixel) for RFOV imaging within a scan time (0.7 s) similar to full FOV imaging. A 2.2‐fold shorter scan time along with a significant reduction of blurring was demonstrated in RFOV images compared with full FOV images for a target spatial resolution of 0.69 mm/pixel.

Conclusion:

RFOV SS‐FSE imaging using a 2DRF pulse shows advantages in scan time, blurring, and specific absorption rate reduction along with true spatial resolution increase compared with full FOV imaging. This approach is promising to benefit fast imaging applications such as image guided therapy. J. Magn. Reson. Imaging 2010;32:242–248. © 2010 Wiley‐Liss, Inc.     

Image registration for targeted MRI-guided transperineal prostate biopsy

Purpose:

To develop and evaluate image registration methodology for automated re‐identification of tumor‐suspicious foci from preprocedural MR exams during MR‐guided transperineal prostate core biopsy.

Materials and Methods:

A hierarchical approach for automated registration between planning and intra‐procedural T2‐weighted prostate MRI was developed and evaluated on the images acquired during 10 consecutive MR‐guided biopsies. Registration accuracy was quantified at image‐based landmarks and by evaluating spatial overlap for the manually segmented prostate and sub‐structures. Registration reliability was evaluated by simulating initial mis‐registration and analyzing the convergence behavior. Registration precision was characterized at the planned biopsy targets.

Results:

The total computation time was compatible with a clinical setting, being at most 2 min. Deformable registration led to a significant improvement in spatial overlap of the prostate and peripheral zone contours compared with both rigid and affine registration. Average in‐slice landmark registration error was 1.3 ± 0.5 mm. Experiments simulating initial mis‐registration resulted in an estimated average capture range of 6 mm and an average in‐slice registration precision of ±0.3 mm.

Conclusion:

Our registration approach requires minimum user interaction and is compatible with the time constraints of our interventional clinical workflow. The initial evaluation shows acceptable accuracy, reliability and consistency of the method. J. Magn. Reson. Imaging 2012;36:987–992. © 2012 Wiley Periodicals, Inc.     

Accuracy and speed of robotic assisted needle interventions using a modern cone beam computed tomography intervention suite: a phantom study

Objective

To analyse the feasibility and accuracy of robotic aided interventions on a phantom when using a modern C-arm-mounted cone beam computed tomography (CBCT) device in combination with needle guidance software.

Methods

A small robotic device capable of holding and guiding needles was attached to the intervention table. After acquiring a 3D data set the access path was planned on the CBCT workstation and shown on the intervention monitor. Then the robot was aligned to the live fluorosopic image. A total of 40 punctures were randomly conducted on a phantom armed with several targets (diameter 2 mm) in single and double oblique trajectory (n?=?20 each). Target distance, needle deviation and time for the procedures were analysed.

Results

All phantom interventions (n?=?40) could be performed successfully. Mean target access path within the phantom was 8.5 cm (min 4.2 cm, max 13.5 cm). Average needle tip deviation was 1.1 mm (min 0 mm, max 4.5 mm), time duration was 3:59 min (min 2:07 min, max 10:37 min).

Conclusion

When using the proposed robot device in a CBCT intervention suite, highly accurate needle-based interventional punctures are possible in a reasonable timely manner in single as well as in double oblique trajectories.

Key Points

? Percutaneous image-guided biopsy is an important contribution of modern radiology. ? A compact robotic device has been developed which may facilitate such procedures. ? Accurate needle-based interventions are possible in a timely manner. ? Complex trajectories and even deep access paths are possible.     

MRI‐guided brain tumor cryoablation in a rabbit model

Purpose

To report the results of an animal trial exploring the feasibility of minimally invasive MR imaging‐guided rabbit brain tumor cryoablation with an argon‐based cryo‐unit.

Materials and Methods

VX₂ tumor segments (0.96 × 0.96 × 50mm) were implanted into parietal lobes of 26 New Zealand white rabbits. Seventeen rabbits were treated with cryoablation. Six rabbits were not treated and formed a control group. Cryoablation was achieved with a MR‐compatible cryoablation unit using 1.47‐mm cryoprobes in an open 0.23 Tesla (T) MRI scanner. The therapeutic response was evaluated with follow‐up MRI and the corresponding histopathology. A 3.0T MRI scanner was used for preoperative and postoperative follow‐up imaging. Posttreatment imaging with subsequent endpoints was performed at 3, 7, 14, and 60 days after the treatment.

Results

Of 17 rabbits, 6 died on the first postoperative day. Histopathology revealed coagulation necrosis in samples from the 3rd, 7th, and 14th day, and reactive changes at 60 days, these findings were consistent with MRI. The longest survival time in the treatment group, 60 days (n = 2), was considerably longer than the survival times in control group.

Conclusion

Successful rabbit brain tumor cryoablation can be achieved using argon‐based cryodevice under MRI guidance. The complication rate in this series was relatively high. J. Magn. Reson. Imaging 2009;29:545–551. © 2009 Wiley‐Liss, Inc.     

Optimal fast T2‐weighted magnetic resonance microscopy imaging of the eye and its clinical application

Purpose:

To compare a half‐Fourier single‐shot rapid acquisition with relaxation enhancement (RARE) sequence with a balanced steady‐state free precession (b‐SSFP) sequence in the evaluation of the eye using magnetic resonance (MR) microscopy imaging and to clarify the usefulness of RARE microscopy imaging in evaluating nonoperative glaucoma patients and patients who have undergone surgery for glaucoma or cataract.

Materials and Methods:

One‐mm and 2‐mm slice thickness images of RARE sequence and b‐SSFP sequence using a 1.5 T MR unit and a 23‐mm microscopy coil were obtained in eight healthy volunteers. The signal‐to‐noise (S/N) ratio of aqueous humor in the anterior chamber was measured quantitatively and visualization of the anterior chamber anatomy was assessed qualitatively. Furthermore, we evaluated 21 glaucoma patients (including six postoperative patients) and four patients after cataract surgery with 2‐mm slice thickness RARE MRI.

Results:

The 2‐mm slice thickness RARE imaging had a significantly greater S/N ratio than the 1‐mm slice thickness RARE imaging (P < 0.05) and acquired the best image quality among the four types of images (P < 0.01). Additionally, 2‐mm slice thickness RARE microscopy imaging could depict anterior chamber anatomy of glaucoma eyes and eyes after cataract surgery.

Conclusion:

We believe that optimal fast T2‐weighted MR microimaging might become a useful ophthalmologic examination technique. J. Magn. Reson. Imaging 2010;31:1210–1214. ©2010 Wiley‐Liss, Inc.     

Evaluation of intraportal venous flow distribution by unenhanced MR angiography using three‐dimensional fast spin‐echo with a selective tagging pulse: Efficacy of subtraction of tag‐on and tag‐off images acquired during a single breath‐hold

Purpose

To evaluate the efficacy of subtracted MR images from two sets of unenhanced three‐dimensional (3D) MR angiography data (tag‐on and tag‐off images) acquired simultaneously during a single breath‐hold in assessing the intraportal venous flow distribution to the distal branches from the superior mesenteric vein (SMV) and the splenic vein (SpV).

Materials and Methods

Tag‐on and tag‐off MR images during a single breath‐hold were obtained in 25 normal subjects. Tagging pulse was placed on the SMV or SpV separately to study inflow correlation of tagged blood into the portal vein.

Results

On the MR images tagged on the SMV, the mean ratings of visibility of tagged blood flow on the subtracted images were significantly higher (P = 0.016–0.0001) than those on the source images in almost all branches except second‐ordered left portal vein (P = 0.096). On the subtracted MR images tagged on SMV, the tramline (16 of the 25 subjects) was the most common distribution pattern of the tagged blood inflow in the main portal vein.

Conclusion

Subtracted MR images from two sets of unenhanced 3D MR angiography data (tag‐on and tag‐off images) acquired simultaneously would be effective to show the blood flow distribution of tagged blood into the portal vein and distal branches from SMV and SpV under the physiological condition without contrast injections. J. Magn. Reson. Imaging 2009;29:1224–1229. © 2009 Wiley‐Liss, Inc.     

Magnetic resonance imaging and three‐dimensional ultrasound of carotid atherosclerosis: Mapping regional differences

Purpose

To evaluate differences in carotid atherosclerosis measured using magnetic resonance imaging (MRI) and three‐dimensional ultrasound (3DUS).

Materials and Methods

Ten subject volunteers underwent carotid 3DUS and MRI (multislice black blood fast spin echo, T1‐weighted contrast, double inversion recovery, 0.5 mm in‐plane resolution, 2 mm slice, 3.0 T) within 1 hour. 3DUS and MR images were manually segmented by two observers providing vessel wall and lumen contours for quantification of vessel wall volume (VWV) and generation of carotid thickness maps.

Results

MRI VWV (1040 ± 210 mm³) and 3DUS VWV (540 ± 110 mm³) were significantly different (P < 0.0001). When normalized for the estimated adventitia volume, mean MRI VWV decreased 240 ± 50 mm³ and was significantly different from 3DUS VWV (P < 0.001). Two‐dimensional carotid maps showed qualitative evidence of regional differences in the plaque and vessel wall thickness between MR and 3DUS in all subjects. Power Doppler US confirmed that heterogeneity in the common carotid artery in all patients resulted from apparent flow disturbances, not atherosclerotic plaque.

Conclusion

MRI and 3DUS VWV were significantly different and carotid maps showed homogeneous thickness differences and heterogeneity in specific regions of interest identified as MR flow artifacts in the common carotid artery. J. Magn. Reson. Imaging 2009;29:901–908. © 2009 Wiley‐Liss, Inc.     

Short echo time 1H MRSI of the human brain at 3T with adiabatic slice‐selective refocusing pulses; reproducibility and variance in a dual center setting

Purpose:

To assess the reproducibility of ¹H‐MR spectroscopic imaging (MRSI) of the human brain at 3T with volume selection by a double spin echo sequence for localization with adiabatic refocusing pulses (semi‐LASER).

Materials and Methods:

Twenty volunteers in two different institutions were measured twice with the same pulse sequence at an echo time of 30 msec. Magnetic resonance (MR) spectra were analyzed with LCModel with a simulated basis set including an experimentally acquired macromolecular signal profile. For specific regions in the brain mean metabolite levels, within and between subject variance, and the coefficient of variation (CoV) were calculated (for taurine, glutamate, total N‐acetylaspartate, total creatine, total choline, myo‐inositol + glycine, and glutamate + glutamine).

Results:

Repeated measurements showed no significant differences with a paired t‐test and a high reproducibility (CoV ranging from 3%–30% throughout the selected volume). Mean metabolite levels and CoV obtained in similar regions in the brain did not differ significantly between two contributing institutions. The major source of differences between different measurements was identified to be the between‐subject variations in the volunteers.

Conclusion:

We conclude that semi‐LASER ¹H‐MRSI at 3T is an adequate method to obtain quantitative and reproducible measures of metabolite levels over large parts of the brain, applicable across multiple centers. J. Magn. Reson. Imaging 2010;31:61–70. © 2009 Wiley‐Liss, Inc.     

Evaluation of a CT-Guided Robotic System for Precise Percutaneous Needle Insertion

Purpose

To assess overall targeting accuracy for CT-guided needle insertion using prototype robotic system for common target sites.

Fluoroscopy-Guided Percutaneous Vertebral Body Biopsy Using a Novel Drill-Powered Device: Technical Case Series

Background

A novel coaxial biopsy system powered by a handheld drill has recently been introduced for percutaneous bone biopsy. This technical note describes our initial experience performing fluoroscopy-guided vertebral body biopsies with this system, compares the yield of drill-assisted biopsy specimens with those obtained using a manual technique, and assesses the histologic adequacy of specimens obtained with drill assistance.

Methods

Medical records of all single-level, fluoroscopy-guided vertebral body biopsies were reviewed. Procedural complications were documented according to the Society of Interventional Radiology classification. The total length of bone core obtained from drill-assisted biopsies was compared with that of matched manual biopsies. Pathology reports were reviewed to determine the histologic adequacy of specimens obtained with drill assistance.

Results

Twenty eight drill-assisted percutaneous vertebral body biopsies met study inclusion criteria. No acute complications were reported. Of the 86 % (24/28) of patients with clinical follow-up, no delayed complications were reported (median follow-up, 28 weeks; range 5–115 weeks). The median total length of bone core obtained from drill-assisted biopsies was 28 mm (range 8–120 mm). This was longer than that obtained from manual biopsies (median, 20 mm; range 5–45 mm; P = 0.03). Crush artifact was present in 11 % (3/28) of drill-assisted biopsy specimens, which in one case (3.6 %; 1/28) precluded definitive diagnosis.

Conclusions

A drill-assisted, coaxial biopsy system can be used to safely obtain vertebral body core specimens under fluoroscopic guidance. The higher bone core yield obtained with drill assistance may be offset by the presence of crush artifact.

     

Quantification of hepatic macrosteatosis in living,related liver donors using T1‐independent,T2*‐corrected chemical shift MRI

Purpose:

To evaluate the diagnostic implications of the iterative decomposition of water and fat using echo‐asymmetry and the least‐squares estimation (IDEAL) technique to detect hepatic steatosis (HS) in potential liver donors using histopathology as the reference standard.

Materials and Methods:

Forty‐nine potential liver donors (32 male, 17 female; mean age, 31.7 years) were included. All patients were imaged using the in‐ and out‐of‐phase (IOP) gradient‐echo (GRE) and IDEAL techniques on a 1.5 T MR scanner. To estimate the hepatic fat fraction (FF), two reviewers performed regions‐of‐interest measurement in 15 areas of the liver seen on the IOP images and on the IDEAL‐FF images. The magnetic resonance imaging (MRI) and pathology values of macrosteatosis were correlated using the Pearson correlation coefficient. We analyzed the diagnostic performance of IOP imaging and IDEAL for detecting HS.

Results:

The results of the hepatic‐FF estimated on IDEAL were well correlated with the histologic degree of macrosteatosis (γ = 0.902, P < 0.001). IDEAL showed 100% sensitivity and 91% specificity for detecting HS, and IOP imaging showed 87.5% sensitivity and 97% specificity, respectively.

Conclusion:

IDEAL is a useful tool for the preoperative diagnosis of HS in potential living liver donors; it can also help to avoid unnecessary biopsies in these patients. J. Magn. Reson. Imaging 2012;36:1124–1130. © 2012 Wiley Periodicals, Inc.