CT-MR Fusion Research Articles

Three-Dimensional Reconstructed Computed Tomography-Magnetic Resonance Fusion Image-Based Preoperative Planning for Surgical Procedures for Spinal Lipoma or Tethered Spinal Cord After Myelomeningocele Repair -Technical Note-

Surgical procedures for spinal lipoma or tethered spinal cord after myelomeningocele (MMC) repair are often difficult and complicated, because the anatomical structures can be deformed in complex and unpredictable ways. Imaging helps the surgeon understand the patient's spinal anatomy. Whereas two-dimensional images provide only limited information for surgical planning, three-dimensional (3D) reconstructed computed tomography (CT)-magnetic resonance (MR) fusion images produce clearer representations of the spinal regions. Here we describe simple and quick methods for obtaining 3D reconstructed CT-MR fusion images for preoperative planning of surgical procedures using the iPlan(®) cranial (BrainLAB AG, Feldkirchen, Germany) neuronavigation software. 3D CT images of the vertebral bone were combined with heavily T(2)-weighted MR images of the spinal cord, lipoma, cerebrospinal fluid (CSF) space, and nerve root through a process of fusion, segmentation, and reconstruction of the 3D images. We also used our procedure called "Image Overlay" to directly project the 3D reconstructed image onto the body surface using an LED projector. The final reconstructed 3D images took 10-30 minutes to obtain, and provided the surgeon with a representation of the individual pathological structures, so enabled the design of effective surgical plans, even in patients with bony deformity such as scoliosis. None of the 19 patients treated based on our 3D reconstruction method has had neurological complications, except for CSF leakage. This 3D reconstructed imaging method, combined with Image Overlay, improves the visual understanding of complicated surgical situations, and should improve surgical efficiency and outcome.

An analysis of intraoperative versus post-operative dosimetry with CT, CT–MRI fusion and XMR for the evaluation of permanent prostate brachytherapy implants

Background and purpose To assess the agreement between intraoperative and post-operative dosimetry and to identify factors that influence dose calculations of prostate brachytherapy implants. Materials and methods Patients treated with prostate brachytherapy implants underwent post-operative CT and XMR (combined X-ray and MR) imaging. Dose–volume histograms were calculated from CT, XMR and CT–MR fusion data and compared with intraoperative values for two observers. Multiple linear regression models assessed the influences of intraoperative D90, gland oedema, gland volume, source loss and migration, and implanted activity/volume prostate on post-operative D90. Results Forty-nine patients were studied. The mean D90 differences (95% confidence limits) between intraoperative and post-operative CT, XMR and CT–MR fusion assessments were: 11 Gy (−22, 45), 18 Gy (−13, 49) and 20 Gy (−17, 58) for Observer 1; and 15 Gy (−34, 63), 13 Gy (−29, 55) and 14 Gy (−27, 54) for Observer 2. Multiple linear regression modelling showed that the observed oedema and intraoperative D90 were significant independent variables for the prediction of post-operative D90 values for both observers using all modalities. Conclusion This is the first study to report Bland–Altman agreement analysis between intraoperative and post-operative dosimetry. Agreement is poor. Post-operative dosimetry is dependent on the intraoperative D90 and the subjectively outlined gland volume.

Reprogramming guided by the fused images of MRI and CT in subthalamic nucleus stimulation in Parkinson disease

Objective To evaluate the usefulness of the visual information about the location of the contacts in deep brain stimulation (DBS) programming, we compared the outcomes of subthalamic nucleus (STN) stimulation before and after reprogramming guided by the fused images of MRI and CT. Methods Of the 65 patients with Parkinson's disease, who underwent bilateral STN-DBS surgery between March 2005 and September 2006 and had been managed for at least 6 months with conventional programming which was only based on the physiological responses from the patients, 54 patients were reprogrammed based on the 3D anatomical location of the contacts revealed by the fused images of pre-operative MRI and post-operative CT scans taken at 6 months after surgery. A total 51 patients completed the evaluation after reprogramming. Results Reprogramming significantly improved the UPDRS part III scores during the on- and off-medication condition. The daily levodopa-equivalent dose was significantly reduced. Improvement in the UPDRS part III scores after reprogramming was greater in the patients with electrodes in the STN than the patients with electrodes off the STN. Conclusions CT-MR fusion images helped to reprogram stimulation parameters with ease and confidence in a time-saving manner and resulted in further clinical improvement. This method could complement the conventional method of adjusting stimulation parameters after bilateral STN-DBS.

The effective application of segmental image fusion in spinal radiosurgery for improved targeting of spinal tumours

As a result of experiences of failed image fusion, an improved protocol for effective CT and MRI image fusion was developed. Image fusion is a critical part of image-guided stereotactic radiosurgery (IG-SRS) and greatly influences the accurate measurement of gross tumour volume (GTV) and optimal dosimetry. Avoidance of any positional discrepancy is vital for optimal image fusion and results in improved targeting, which improves clinical results. This paper describes a protocol for effective image fusion and how it impacted on the clinical outcome of stereotactic radiosurgery for spinal tumours. Fused MRI/CT images from 20 patients were examined and compared. A protocol for fusing images from thin slice MR images and CTs was developed for improved identification and measurement of tumour volume. Differences in individual GTV values both before and after image fusion were evaluated. The effectiveness of tumour targeting was also assessed by comparing discrepancies in individual and overall GTV values. Differences in mean GTVs using either CT or MRI alone compared with the mean found through combined CT/MR image fusion showed a difference of 30.5 +/- 4.8% and 14.5 +/- 3.3% respectively. Additionally, the median GTV values from CT- and MR-based imaging were 11.64 +/- 7.8 cm(3) and 11.72 +/- 6.6 cm(3) vs 14.06 +/- 8.0 cm(3). Median GTV from CT-MR fusion was 14.06 +/- 8.0 cm(3). Improved information provided by the fused images enabled us to prescribe more effective dosages, as the fused images gave more accurate information about tumour se due to better delineation of tumour perimeters. This protocol provides improved visualisation of spinal tumours and enables better treatment planning. Segmented image fusion was shown to provide significant advantages for planning stereotactic radiosurgery. Fused images provided more precise and accurate data and allowed better targeting of tumours, with improved tumour coverage that resulted in better clinical outcomes.

CT–MR image data fusion for computer-assisted navigated surgery of orbital tumors

Purpose To demonstrate the value of multidetector computed tomography (MDCT) and magnetic resonance imaging (MRI) in the preoperative assessment of orbital tumors, and to present, particularly, CT and MR image data fusion for surgical planning and performance in computer-assisted navigated surgery of orbital tumors. Materials and methods In this retrospective case series, 10 patients with orbital tumors and associated complaints underwent MDCT and MRI of the orbit. MDCT was performed at high resolution, with a bone window level setting in the axial plane. MRI was performed with an axial 3D T1-weighted (w) gradient-echo (GE) contrast-enhanced sequence, in addition to a standard MRI protocol. First, MDCT and MR images were used to diagnose tumorous lesions compared to histology as a standard of reference. Then, the image data sets from CT and 3D T1-w GE sequences were merged on a workstation to create CT–MR fusion images that were used for interventional planning and intraoperative image guidance. The intraoperative accuracy of the navigation unit was measured, defined as the deviation between the same landmark in the navigation image and the patient. Furthermore, the clinical preoperative status was compared to the patients’ postoperative outcome. Results Radiological and histological diagnosis, which revealed 7 benign and 3 malignant tumors, were concordant in 7 of 10 cases (70%). The CT–MR fusion images supported the surgeon in the preoperative planning and improved the surgical performance. The mean intraoperative accuracy of the navigation unit was 1.35 mm. Postoperatively, orbital complaints showed complete regression in 6 cases, were ameliorated notably in 3 cases, and remained unchanged in 1 case. Conclusion CT and MRI are essential for the preoperative assessment of orbital tumors. CT–MR image data fusion is an accurate tool for planning the correct surgical procedure, and can improve surgical results in computer-assisted navigated surgery of orbital tumors.

Loose seeds vs. stranded seeds: A comparison of critical organ dosimetry and acute toxicity in 125I permanent implant for low-risk prostate cancer

Purpose To compare the critical organ dosimetry and toxicity of loose seeds (LS) with stranded seeds (SS) in 125I permanent implant for low-risk prostate cancer. Methods and Materials Two cohorts of 20 patients each were treated in Institutional Review Board–approved protocols designed to assess prostate edema and seed stability using MR–CT fusion on Days 0, 7, and 30 after permanent implant. 125I LS were used for one cohort and 125I SS for the other. Rectal wall dosimetry was compared for the two cohorts using RV100 and RD1 cc and urethral dosimetry using UD5, UD30, and UV150. Statistical comparisons were performed using unpaired Student's t test. Results At each time point (Days 0, 7, and 30), both the mean RD1 cc (SS: 123.1, 139.7, and 156.1 Gy vs. LS: 90.2, 104, and 129.4 Gy, respectively) and the mean RV100 (SS: 0.63, 1.0, and 1.4 cc vs. LS: 0.2, 0.4, and 0.73 cc, respectively) were significantly higher for strands (all p-values < 0.01). Only 1 patient developed radiotherapy oncology group (RTOG) Grade 1 acute rectal toxicity in the loose seed cohort, whereas 3 patients had Grade 1 and 1 patient had Grade 2 toxicity with strands. The mean percentage increase of UD5 (7.7% LS vs. 24.6% SS; p = 0.004) and UD30 (5% LS vs. 15.9% SS; p = 0.02) from preplan to Day 30 was higher for strands. The increase in UV150 from baseline to Day 30 was significantly higher for strands (0.2 vs. 0.06 cc; p = 0.01). Urinary toxicity was similar in both cohorts. Conclusions SS resulted in higher dose to urethra and rectal wall compared with LS on postimplant dosimetry. A trend toward higher acute rectal toxicity rate was observed for SS.

Whole Brain Radiation Therapy With Hippocampal Avoidance and Simultaneously Integrated Brain Metastases Boost With Helical Tomotherapy: A Planning Study

Purpose/Objective(s): To evaluate the feasibility of using tomotherapy to deliver whole brain radiotherapy (WBRT) with hippocampal avoidance, hypothesized to reduce the risk of memory function decline, and simultaneously integrated boost to brain metastases to improve intra-cranial tumor control. Materials/Methods: Ten patients treated with radiosurgery and WBRT were replanned on tomotherapy using original CT scans and MR-CT fusion defined target and normal structure contours. Individually contoured hippocampus and amygdale were used as dose-limiting structures (<6Gy); the whole brain dose was prescribed at 32.25 Gy to 95% in 15 fractions and simultaneous boost doses to individual brain metastases were 63 Gy to lesions ≥ 2.0 cm in maximum diameter, and 70.8 Gy to lesions < 2.0 cm. Plans were generated with a field width (FW) of 2.5 cm, and in five patients with FW of 1.0 cm. Plans were compared regarding prescription isodose to target volume (PITV) ratio, target coverage (TC), conformation number (CN), homogeneity index (HI), and mean normalized total dose (NTDmean). Results: A 1.0 cm compared with 2.5 cm FW significantly improved the dose distribution. Mean PITV ratio improved from 1.75 ± 0.61 to 1.48 ± 0.37. Whole brain homogeneity (HI) improved by 32% (p < 0.0004) due to the sharper dose gradients afforded by a smaller FW. NTDmean to the hippocampus was 5.9 ± 1.3 and 5.8 ± 1.9Gy2, for 2.5 and 1.0 cm FW, respectively. Mean treatment delivery time for 2.5 and 1.0 cm FW plans was 10.2 ± 1.0 and 21.8 ± 1.8 minutes. Conclusions: Composite tomotherapy plans achieved 3 objectives: homogeneous whole brain dose distribution equivalent to conventional WBRT; conformal hippocampal avoidance; radiosurgicallyequivalent dose distributions to individual metastases.

CT–MR image data fusion for computer assisted navigated neurosurgery of temporal bone tumors

Purpose To demonstrate the value of multi detector computed tomography (MDCT) and magnetic resonance imaging (MRI) in the preoperative work up of temporal bone tumors and to present, especially, CT and MR image fusion for surgical planning and performance in computer assisted navigated neurosurgery of temporal bone tumors. Materials and methods Fifteen patients with temporal bone tumors underwent MDCT and MRI. MDCT was performed in high-resolution bone window level setting in axial plane. The reconstructed MDCT slice thickness was 0.8 mm. MRI was performed in axial and coronal plane with T2-weighted fast spin-echo (FSE) sequences, un-enhanced and contrast-enhanced T1-weighted spin-echo (SE) sequences, and coronal T1-weighted SE sequences with fat suppression and with 3D T1-weighted gradient-echo (GE) contrast-enhanced sequences in axial plane. The 3D T1-weighted GE sequence had a slice thickness of 1 mm. Image data sets of CT and 3D T1-weighted GE sequences were merged utilizing a workstation to create CT–MR fusion images. MDCT and MR images were separately used to depict and characterize lesions. The fusion images were utilized for interventional planning and intraoperative image guidance. The intraoperative accuracy of the navigation unit was measured, defined as the deviation between the same landmark in the navigation image and the patient. Results Tumorous lesions of bone and soft tissue were well delineated and characterized by CT and MR images. The images played a crucial role in the differentiation of benign and malignant pathologies, which consisted of 13 benign and 2 malignant tumors. The CT–MR fusion images supported the surgeon in preoperative planning and improved surgical performance. The mean intraoperative accuracy of the navigation system was 1.25 mm. Conclusion CT and MRI are essential in the preoperative work up of temporal bone tumors. CT–MR image data fusion presents an accurate tool for planning the correct surgical procedure and is a benefit for the operational results in computer assisted navigated neurosurgery of temporal bone tumors.

Advances in imaging of the paranasal sinuses

Imaging technology has played a significant role in the diagnosis and management of sinonasal disorders. Plain sinus films are almost exclusively replaced by CT in the work-up for inflammatory sinus disease. MRI provides complementary information to CT in cases of sinonasal and skull-base neoplasms. The evolution of endoscopic surgical techniques for the paranasal sinuses and skull base is made possible by the parallel advancement of imaging technologies. Recent advances that are currently in clinical use have included multidetector row CT scanners and computer image-guidance systems for surgery. Three-dimensional CT angiography, image-guided CT-MR fusion, and intraoperative image-guidance are new techniques that are currently being evaluated. As imaging technology continues to advance, so does the capability to treat diseases beyond the sinuses and skull base with minimally invasive, endoscopic approaches.

CT-MR image fusion for the management of skull base lesions

Image fusion software creates composite images from computed tomography (CT) and magnetic resonance (MR) images. CT-MR fusion studies between August 2004 to July 2005 were reviewed. CT scan images (1-mm axial) were obtained on a multi-detector CT scanner. MR images (1-mm axial) were obtained with a T1-weighted, volume acquisition technique. CT-MR fusion images were created on the Instatrak 3500 Plus or CBYON Suite. A total of 25 patients had 27 CT-MR image fusion studies. CT-MR fusion accuracy was 2 mm or better. During preoperative planning and intraoperative navigation, CT-MR fusion facilitated the delineation of the anatomic relationships between the lesion and the skull base. CT-MR image fusion yields composite images that combine features of each component imaging modality. Image fusion, when combined with surgical navigation, further enhances potential skull base applications for minimally invasive endoscopic surgery.

Comparison of linac based fractionated stereotactic radiotherapy and tomotherapy treatment plans for skull-base tumors

Background and purpose To compare and evaluate helical tomotherapy and linac based fractionated stereotactic radiotherapy (FSRT) techniques in the treatment of skull-base tumors. Patients and methods Ten patients diagnosed with skull-base tumors, originally planned for optically guided FSRT to prescribed doses of 50.4–54 Gy were replanned for treatment with clinically deliverable helical tomotherapy. All original CT scans, MR-CT fusion defined target and normal structure contours, and PTV margins were used for helical tomotherapy planning. Linac based plans utilized one of the following FSRT planning techniques: non-coplanar or coplanar intensity modulated radiation therapy (IMRT), multiple non-coplanar conformal arcs, and non-coplanar conformal radiation therapy (CRT). These plans were used as the standard to which the subsequent tomotherapy plans were compared, using the following criteria: prescription isodose to target volume (PITV) ratios, an inhomogeneity index (II), equivalent uniform dose (EUD) for PTV volumes, mean normalized total doses (NTD mean) for critical structures, and size of 10, 20, and 30 Gy isodose volumes. Results Use of both linac based FSRT techniques and helical tomotherapy generated highly conformal treatment plans. Tomotherapy plans, which are predominantly coplanar in nature, compared to non-coplanar linac based plans exhibited increased PITV ratios, variable change in II, similar EUD values, and generally comparable NTD mean values for organs at risk. When compared to non-coplanar field arrangements, deliverable (as opposed to idealized) tomotherapy plans also resulted in 13–540% increases in low dose isodose volumes. All criteria except for the II, which was generally improved with tomotherapy, were found to be similar when coplanar linac based plans were compared to helical tomotherapy plans. Conclusions Results show a distinct advantage in using non-coplanar beam arrangements for treatment of skull-base tumors. In the case where disease spreads far inferiorly, limiting the ability to use non-coplanar arrangements, helical tomotherapy can be used to generate a comparable treatment plan, with potentially superior homogeneity.

75 poster CT-MR fusion for the treatment plan of pituitary adenoma

75 poster CT-MR fusion for the treatment plan of pituitary adenoma

Can the anatomical location of the prostatic neurovascular bundle and the penile bulb be reliably determined for the purpose of online “nerve-sparing” image-guided radiation therapy in prostate cancer? an MR-CT 3D fusion imaging study

Purpose/Objective: Erectile dysfunction (ED) is the most frequent late toxicity after radiation therapy in patients with prostate cancer. The etiology is multifactorial but most likely radiation-induced vascular and neurological damage at the level of prostatic neurovascular bundle (NVB) and penile bulb (PB) is the predominant factor. While there are reports suggesting a dose-effect relationship between PB total irradiation dose and ED, the studies looking at NVB total irradiation dose and ED failed to establish a clear correlation. This finding may be partly due to the difficulty in identifying the NVB on the CT scan images. As a prerequisite of online “nerve-sparing” image-guided radiotherapy (IGRT), we used fusion and 3D matching algorithms in 15 MR-CT imaging data sets to assess the accuracy and precision of locating the NVB and the PB on CT images as compared to MR.

Numerical determination of the susceptibility caused geometric distortions in magnetic resonance imaging

The goal of this work is the design of highly accurate surgical navigation methods purely based on magnetic resonance imaging. In this context we numerically examine the geometrical distortions which occur in magnetic resonance imaging. We extend an existing method for computing magnitude and direction of distortions for any internal point. In particular, a multi-grid approach for a fast and efficient calculation of the static magnetic field throughout the imaging volume is presented and compared to the analytical solution for simple geometries. We found that shifts in the range of up to 2.5 mm occur in MRI of femur bones with 1.5 Tesla. Our new method was implemented and has been found capable of accurately correcting for geometrical distortions within reasonable computing times. In particular, we show that the registration accuracy for mutual information (MI) based MR-CT fusion can be much improved. Thus the value of the optimization functional in MI registration for MR-CT substantially increases after our distortion correction.

A quantitative comparison of CT alone vs. CT/MR image fusion in radiation treatment planning of glioblastoma multiforme: is there added value with MR

Purpose/Objective: CT/MR fusion technology is commonly used in the radiation treatment planning of primary brain tumors. The MR images allow for more precise definition of edema, which has a high probability of containing cancerous cells and should be included in the treatment volume. The enhancement of the lesion itself is better demarcated by the MR when compared to the CT. Many feel the CT/MR technology is superior to CT alone, however, there has been little quantification of the difference between the two when looking at the treatment planning of Glioblastoma Multiforme (GBM). In other words, what is the added value of the MR? We sought to numerically quantify the deviation in volume coverage and dose delivered if one were to plan and treat with a CT scan alone as opposed to utilizing the CT/MR fusion images. Materials/Methods: Twelve sequential patients were selected from an institutional database. All patients had received a CT and MR with contrast. These two image sets were then fused utilizing the AcQSim® Image Fusion Software. The edema (initial GTV) and gross tumor (CT GTV) were individually contoured using the image data from both scans, and a 1.5cm margin was added to form the CTV’s. A 0.5cm margin was added to the CTV’s to achieve an initial and boost PTV. The initial PTV was prescribed a dose of 4500-5040 cGy and the boost PTV was prescribed an additional dose for a total of 5940 cGy. We retrospectively replanned these cases using only the CT images. The CT-only image sets were then contoured in a similar fashion to the original CT/MR fusion data sets and planned to the same initial and boost treatment doses. Dose-volume histograms were then created of the CT-only plan for the CT-only volume and the CT-only plan for the CT/MR fusion volume, and compared to the original CT/MR fusion plan for the CT/MR fusion volume. Results: Our initial comparison of the CT-only plan and the CT-MR fusion plan showed the median D95 (in cGy) for the CT-only plan PTV and the original CT/MR fusion PTV was 5879 cGy and 5873 cGy, respectively, and the median V95 (in % volume) for the CT plan and CT/MR fusion plan was 98% and 99.5%, respectively. Thus, the plans were equally conformal. When CT-only plans were used, the CT/MR fusion volume was missed by a median V95 of 7% and 4.5% for the initial and boost doses, respectively. As shown in figure 1, these volumes differed from patient to patient. As would be expected, the D95’s were larger for the CT/MR fusion plan than they were for the CT-only plan. Conclusions: The MRI volumes were, in general, only slightly larger than the CT volumes. However, a few patients had a marked difference. We believe the differences in volume and thereby dose coverage arose from the enhanced resolution of the edema and tumor seen on the MRI. We believe that the added time and expense of obtaining an MRI should continue to be practiced in the radiation treatment of GBM as 3 of our 12 patients had greater than 10% of the volume underdosed. View Large Image Figure ViewerDownload (PPT)

P-5-641 - Orbital masses approaches

To assess the agreement between intraoperative and post-operative dosimetry and to identify factors that influence dose calculations of prostate brachytherapy implants.Patients treated with prostate brachytherapy implants underwent post-operative CT and XMR (combined X-ray and MR) imaging. Dose–volume histograms were calculated from CT, XMR and CT–MR fusion data and compared with intraoperative values for two observers. Multiple linear regression models assessed the influences of intraoperative D90, gland oedema, gland volume, source loss and migration, and implanted activity/volume prostate on post-operative D90.Forty-nine patients were studied. The mean D90 differences (95% confidence limits) between intraoperative and post-operative CT, XMR and CT–MR fusion assessments were: 11 Gy (−22, 45), 18 Gy (−13, 49) and 20 Gy (−17, 58) for Observer 1; and 15 Gy (−34, 63), 13 Gy (−29, 55) and 14 Gy (−27, 54) for Observer 2. Multiple linear regression modelling showed that the observed oedema and intraoperative D90 were significant independent variables for the prediction of post-operative D90 values for both observers using all modalities.This is the first study to report Bland–Altman agreement analysis between intraoperative and post-operative dosimetry. Agreement is poor. Post-operative dosimetry is dependent on the intraoperative D90 and the subjectively outlined gland volume.