Computed Tomography Magnetic Resonance Research Articles

Distinguishing Tumefactive Demyelinating Lesions from Glioma or Central Nervous System Lymphoma: Added Value of Unenhanced CT Compared with Conventional Contrast-enhanced MR Imaging

To determine retrospectively whether unenhanced computed tomographic (CT) images of the brain have added value in distinguishing tumefactive demyelinating lesions (TDLs) from primary glioma or central nervous system (CNS) lymphoma, compared with conventional contrast material-enhanced magnetic resonance (MR) images only. This study was approved by the institutional review board, and informed consent was waived. Unenhanced CT and MR images in 15 patients with TDLs (seven women, eight men; mean age, 42 years; range, 27-57 years) and 48 patients with primary brain tumor (27 women, 21 men; mean age, 48 years; range, 19-70 years; 10 lymphomas, 38 gliomas) were retrospectively reviewed. The CT attenuation of regions that were enhanced or unenhanced at MR imaging was visually categorized into three grades, and CT attenuation values were determined quantitatively. The diagnostic accuracy of MR imaging for differentiating TDLs from tumors was compared with that of MR imaging plus CT. The following MR imaging features were found more frequently in patients with TDL than in those with brain tumor: incomplete rim enhancement, mixed T2-weighted iso- and hyperintensity of enhanced regions, absence of a mass effect, and absence of cortical involvement (all P values < .05). CT hypoattenuation of MR enhanced regions was observed in 14 (93%) of 15 patients with TDL but in only two (4%) of 48 patients with tumor. The CT attenuation of MR enhanced regions was significantly lower for patients with TDL than for those with tumor (P < .001). The diagnostic accuracy of CT plus MR imaging was significantly higher than that of MR imaging alone (97% vs 73.0%, respectively; P < .001), and the diagnostic accuracy of CT was significantly higher than that of unenhanced T1-weighted MR imaging (95% vs 63%, P < .001). Unenhanced CT plus MR imaging was more accurate for distinguishing TDLs from glioma or CNS lymphoma than contrast-enhanced MR imaging alone.

Complications of Continuous Ambulatory Peritoneal Dialysis

Continuous ambulatory peritoneal dialysis (CAPD) is used to treat end-stage renal failure in an increasing number of patients. CAPD has an advantage over hemodialysis in that it allows patients greater freedom to perform daily activities; it also provides other clinical benefits. However, the long-term effectiveness of CAPD is limited by complications, which have various causes. Complications with an infectious cause include bacterial peritonitis, tuberculous peritonitis, and infections of the catheter exit site and tunnel. Noninfectious complications include catheter dysfunction, dialysate leakage, hernias, and sclerosing encapsulating peritonitis. Many imaging modalities-radiography, ultrasonography, peritoneal scintigraphy, computed tomography (CT), and magnetic resonance (MR) imaging-are useful for characterizing these complications. CT peritoneography and MR peritoneography are techniques specifically suited to this purpose. Imaging plays a critical role in ensuring that complications are detected early and managed appropriately.

What Is the Current Role of CT Urography and MR Urography in the Evaluation of the Urinary Tract?

Technologic advances in both computed tomography (CT) and magnetic resonance (MR) imaging have resulted in the ability to image the urinary tract in ways that surpass the prior mainstay of urinary tract imaging, the intravenous urogram. In adults, for most, if not all, historical indications for intravenous urography, CT urography or MR urography is now the preferred examination. Although a variety of techniques for both examinations have been described, each test provides more diagnostic information than does intravenous urography. With the introduction of multidetector technology, CT urography, to date, has emerged as the initial heir apparent to intravenous urography; many years of experience have now clearly demonstrated that CT is the test of choice for many urologic problems, including urolithiasis, renal masses, urinary tract infection, trauma, and obstructive uropathy. CT urography provides a detailed anatomic depiction of each of the major portions of the urinary tract--the kidneys, intrarenal collecting systems, ureters, and bladder--and thus allows patients with hematuria to be evaluated comprehensively. MR urography can be used also to evaluate the urinary tract and has the advantage of not using ionizing radiation and the potential to provide more functional information than CT. However, MR urography is less established and less reliably results in diagnostic image quality relative to CT urography. Although both tests can be used to evaluate the urinary tract, several issues remain and include reaching a consensus on the optimal protocols and appropriate utilization in an era of cost containment and heightened concerns about radiation exposure.

Radiologic Monitoring of Hepatocellular Carcinoma Tumor Viability after Transhepatic Arterial Chemoembolization: Estimating the Accuracy of Contrast-enhanced Cross-sectional Imaging with Histopathologic Correlation

Cross-sectional diagnostic imaging studies such as contrast-enhanced quadruple-phase helical computed tomography (CT) and contrast-enhanced magnetic resonance (MR) imaging are routinely performed to evaluate tumor response to transhepatic arterial chemoembolization. However, the true correlation between imaging characteristics and histopathologic tumor viability is not known. The aim of the present retrospective study was to determine the sensitivity and specificity of contrast-enhanced CT and contrast-enhanced MR imaging with use of histopathologic analysis. Between February 2002 and October 2005, a total of 31 patients (age, 51-74 years; mean, 60 y) who had undergone chemoembolization underwent follow-up diagnostic cross-sectional imaging before transplantation. The mean time interval between the imaging study and transplantation was 32 days (range, 1-117 d). Imaging studies were assessed for residual or recurrent tumor and were then correlated to the findings of histopathologic analysis performed on the surgical specimens at the time of transplantation. The overall sensitivity and specificity rates of cross-sectional imaging studies were 35% and 64%, respectively. The overall accuracy rate of CT was 43%, with 36% sensitivity and 57% specificity. The overall accuracy rate of MR imaging was 55%, with 43% sensitivity and 75% specificity. Gross macroscopic disease was missed in one patient (9%) who underwent MR imaging and four patients (19%) who underwent CT. Contrast-enhanced CT and MR imaging after chemoembolization are associated with high error rates. Between the two modalities, MR has higher sensitivity and specificity and may be a preferable imaging tool for patients who have undergone chemoembolization.

Radiologist supply and workload: international comparison

The aim of this study was to compare radiology statistics and procedures across the world with an eye to lightening the workload of radiologists in Japan. Literature and data in the public domain were obtained for Organization for Economic Cooperation and Development (OECD) member countries. This study collected and analyzed the number of (diagnostic) radiologists and physicians, computed tomography/magnetic resonance (CT/MR) units, CT/MR examinations, and workload of radiologists. Data for the number of radiologists and CT/MR units were obtained from 26 countries and, among them, data for the number of CT/MR examinations for 17 countries. The study found that in 2004 Japan had only 36 radiologists per million population, which is one-third the national average of the 26 countries surveyed, making Japan one of the lowest ranked countries. The workload of a radiologist (CT/MR examinations/year) in Japan was calculated at 6130. This is 4.3 times the global average (1440 for the 17 countries). This comparison showed that the number of radiologists in Japan is the lowest among the 26 countries, and the workload is the highest. The study also showed that for Japan to provide sustainable and quality health care 8614 diagnostic radiologists--2.5 times the present number- -would be required.

Which Study When? Is Gadolinium-enhanced MR Imaging Safer than Iodine-enhanced CT?1

Jeffrey C. Weinreb, MD The emergence of an association between gadolinium-based contrast agents and nephrogenic systemic fibrosis (NSF), a rare debilitating and sometimes fatal disease, has led to a reassessment of the relative risks of contrast material–enhanced CT and contrast-enhanced MR imaging, particularly in patients with compromised renal function. Now, along with all the other risks, the potential dangers and associated costs of NSF have to be weighed. This article explores the relative risks associated with the use of intravenous iodinated contrast agents and gadolinium-based contrast agents and shows that contrast-enhanced MR imaging is still extremely safe for the majority of patients and has some advantages compared with contrast-enhanced CT for many of them. Intravenous contrast agents are commonly used for both computed tomography (CT) and magnetic resonance (MR) imaging to aid in the detection, characterization, and staging of disease. Despite their use in tens of millions of procedures every year, there are relatively few serious and lifethreatening events. Nevertheless, administration of both the iodinated contrast agents (ICAs) for CT and the gadolinium-based contrast agents (GBCAs) for MR imaging can raise a range of safety concerns, particularly in certain increased-risk population groups, and radiologists are frequently confronted with a dilemma: When either ICA-enhanced CT or GBCA-enhanced MR imaging could provide the relevant diagnostic information, which is the safer and preferred examination, especially in a patient with compromised renal function. Although there is a plethora of literature concerning the association between ICAs and adverse events, there is still much uncertainty about how this information should be integrated into routine practice in an effort to mitigate or eliminate adverse events (1). Despite this uncertainty, until recently there were at least two principles upon which most radiologists agreed and have long been components of the radiology canon: Overall, GBCAs are associated with a lower incidence of adverse events than ICAs, and GBCAs are safer than ICAs in patients with compromised renal function.

Reperfused Myocardial Infarction: Contrast-enhanced 64-Section CT in Comparison to MR Imaging

To prospectively compare 64-section multidetector computed tomography (CT) and cardiac magnetic resonance (MR) imaging for the early assessment of myocardial enhancement and infarct size after acute reperfused myocardial infarction (MI). The study was HIPAA compliant and was approved by the institutional review board. All participants gave written informed consent. Twenty-one patients (18 men; mean age, 60 years +/- 13 [standard deviation]) were examined with 64-section multidetector CT and cardiac MR imaging 5 days or fewer after a first reperfused MI. Multidetector CT was performed during the first pass of contrast material to assess myocardial perfusion and detect microvascular obstruction (no reflow). In 15 patients, a second scan was performed 7 minutes later to assess total infarct size by using delayed hyperenhancement. Early hypoenhancement and delayed hyperenhancement were compared between multidetector CT and cardiac MR imaging with Pearson correlation coefficient and Bland-Altman analysis. Early hypoenhancement was recognized on all multidetector CT and cardiac MR images. Delayed hyperenhancement was observed with cardiac MR imaging at all examinations and with multidetector CT at 11 of 15 examinations. While signal intensity differences between hypoperfused and normal myocardium were comparable for first-pass multidetector CT and cardiac MR imaging, cardiac MR imaging had a far better contrast-to-noise ratio (CNR) for delayed acquisitions than did CT (P < .001). Hypoenhanced areas (as a percentage of left ventricular mass) at first-pass multidetector CT (11% +/- 6) correlated well with those at first-pass cardiac MR imaging (7% +/- 4, R(2) = 0.72). Delayed-enhancement multidetector CT (13% +/- 9) correlated well with delayed-enhancement cardiac MR imaging (15% +/- 7, R(2) = 0.55). Quantification of delayed hypoenhancement (n = 12) had very good correlation between multidetector CT (4% +/- 4) and cardiac MR imaging (3% +/- 2) (R(2) = 0.85). Early and late hypoenhancement showed good CNR and correlated well between multidetector CT and cardiac MR imaging.

An Evaluation of Conformal and Intensity-modulated Radiotherapy in Whole Ventricular Radiotherapy for Localised Primary Intracranial Germinomas

Aims To evaluate different treatment techniques in whole ventricular radiotherapy (WVRT) for localised intracranial germinomas with respect to target volume and organ at risk (OAR) dose. As a second end point, a comparison of OAR doses between WVRT and whole brain radiotherapy was made. Materials and methods Co-registered computed tomography–magnetic resonance images (MRI) of five patients were studied. Planning target volumes for whole ventricles (phase 1, PTV 1) and boost to the primary tumour (phase 2, PTV 2) were prescribed to 24 and 16 Gy. For phase 1, lateral parallel-opposed pairs (PP), non-coplanar three- and four-field (3F and 4F) and optimised four- and seven-field intensity-modulated radiotherapy (4FIMRT and 7FIMRT) plans were compared. A conformal non-coplanar six-field technique was used for phase 2. Results For phase 1, statistically significant high-dose sparing of normal brain was achieved with increasing treatment complexity for supratentorial brain (STB) minus PTV 1 (STB–PTV 1) and infratentorial brain (ITB) minus PTV 1 (ITB–PTV 1). Median pituitary gland dose sparing was 1 Gy with IMRT techniques ( P = not significant). Conclusion WVRT using 7FIMRT is the most conformal technique, which offers significant sparing of normal brain from high-dose irradiation, a mean reduction of 1 Gy in the pituitary gland ( P < 0.05) with no significant reduction in other OARs. Yet even with the most complex technique the absolute reduction in mean dose to normal brain tissue achieved was modest in clinical terms. Whether this could translate into a reduction in late sequelae in a predominantly adolescent patient population remains hypothetical.

Comparison of Low-Dose CT and MR for Measurement of Intra-Abdominal Adipose Tissue: A Phantom and Human Study

The aim of this study was to determine the accuracy and reproducibility of low-dose computed tomography (CT) and magnetic resonance (MR) for abdominal adipose tissue quantification on phantom and human studies. An adiposity phantom (with known internal/external oil volumes) was scanned at three different tube voltages (140, 120, and 90 kVp) using a 16-detector row CT scanner and was imaged using a T1-weighted spin echo MR sequence. For human studies, whole-volume coverage of the abdomen was obtained using CT (at 140 and 90 kVp) and T1-weighted spin echo MR imaging from five obese male volunteers (mean age, 40.6 years; mean body mass index, 30.2). The volumes of total, visceral, and subcutaneous adipose tissues (TAT, VAT, and SAT, respectively) were calculated independently by two radiologists for each CT scan and MR imaging using a computer-aided semiautomatic program. The estimated radiation dose could be reduced by approximately 75% with a 90-kVp protocol as compared with the 140-kVp protocol. Phantom studies showed that there was no statistically significant difference between the four methods in estimating the percentage predicted of the true volumes (measurement errors <4% for all methods, P > .05). In human studies, we found no statistically significant difference between the three methods in TAT, VAT, and SAT volumes (P > .05). Inter- and intraobserver reproducibilities of the CT volume estimates using the 90-kVp protocol were better than those obtained from MR imaging (kappa > 0.9 versus 0.4-0.5; coefficient of variation < 1% versus 15-22%). Low-dose CT provides accurate and reproducible measurement of abdominal adipose tissue volumes with a relevant dose reduction.

Can contrast-enhanced ultrasonography characterize focal liver lesions and differentiate between benign and malignant, thus providing a one-stop imaging service for patients?

Purpose Contrast-enhanced ultrasonography (CEUS) displays high sensitivity and specificity in characterizing focal liver lesions (FLLs). We attempted to determine how often CEUS provides an unequivocal diagnosis of FLLs that does not require additional imaging studies. Materials and methods Seventy-three patients with 146 FLLs were scanned with B-mode, Doppler, and contrast-enhanced US (2 × 2.4 ml SonoVue, low MI, 4–6 MHz curved array transducer, Toshiba Aplio/Siemens–Acuson Sequoia). Data were digitally stored and transferred to a work station with the GE PACS system. Images were reviewed by a consultant radiologist experienced in CEUS and interpreted in accordance with the criteria for characterizing FLLs published by the European Federation of Societies for Ultrasound in Medicine and Biology. Diagnoses were compared with those based on computed tomography (CT) and/or magnetic resonance (MR) findings if these were available. However, our aim was to assess the frequency with which CEUS provided diagnoses that were considered reliable enough to exclude the need for other imaging studies. Therefore, the CEUS diagnoses were not necessarily confirmed by other methods. Results Based on CEUS findings alone, 130/146 (89.0%) FLLs could be classified as benign or malignant, and in 118/146 (80.8%) cases, the lesion could be specifically identified. The other 28/146 (19.2%) FLLs could not be characterized based on CEUS data alone. In 58 (80.8%) of the 73 patients with multiple FLLs, CEUS findings were sufficient to establish the benign vs. malignant nature of all the patient's lesions; in 51/73 (69.9%) patients, all the lesions could also be characterized with CEUS. In the remaining cases, at least one lesion required additional imaging to determine whether it was malignant (14/73, 19.2%) or to establish its identity (22/73, 30.1%). In 4/73 (5.5%) patients, CEUS revealed additional lesions not detected on B-mode US. Conclusions CEUS alone was sufficient to classify 89.0% of the FLLs as benign or malignant, and in 80.8% it was also regarded as sufficient to identify the lesion. It served as a one-stop diagnostic test for 80.8% of the patients, reducing the need for CT–MR scans and providing savings in terms of radiation exposure, time, and money.

Intraductal papillary mucinous neoplasms of the pancreas: correlation of helical CT and dynamic MR imaging features with pathologic findings

We assessed the imaging features of intraductal papillary mucinous neoplasms (IPMNs) of the pancreas paying special attention to underlying pancreatic fibrosis on three-phase helical computed tomography (CT) and dynamic magnetic resonance (MR) imaging. Sixteen patients with histopathologically proven IPMNs underwent three-phase helical CT and dynamic MR imaging. IPMNs were seen as a cluster of cyst-like structures in branch duct (n = 5) and combined types (n = 10), and as a fusiform appearance in the main duct type (n = 1). IPMN shape was most easily visualized at the portal venous dominant phase or delayed phase owing to rim-like enhancement of the dilated ducts. Pathologically mild to severe fibrosis was seen on this enhanced rim replacing the surrounding pancreatic parenchyma. Communication between the dilated branch ducts and main pancreatic duct was identified in 15 patients on helical CT and 14 patients on dynamic MR imaging. In patients with fibrosis of pancreatic parenchyma surrounding this, communication was most easily visualized at the later phase on CT and MR imaging. Adenocarcinomas were depicted as papillary projections in eight of nine patients on CT and MR imaging. Invasion of the pancreatic parenchyma was seen in five of six patients as a solid mass in the pancreatic parenchyma. These masses were most easily visualized at the arterial dominant phase on both CT and MR imaging. Three-phase helical CT and dynamic MR imaging were useful in the diagnosis of IPMN of the pancreas.

World's first magnetic resonance imaging/x-ray/operating room suite: a significant milestone in the improvement of neurosurgical diagnosis and treatment

In February 2006, the magnetic resonance/x-ray/operating room (MRXO) suite opened at the authors' institution. This is the first hybrid neurosurgical procedure suite to combine magnetic resonance (MR) imaging, computed tomography (CT), and angiography within a neurosurgical operating room (OR). In the present paper the authors describe the concept of the MRXO as well as their first 10 months of experience using this suite, and discuss its advantages and limitations. In the MRXO suite, the combined OR and angiography (OR-angiography) station is located in the middle of the suite, and the MR imaging and CT scanning stations are each installed in an adjoining bay connected to the OR-angiography station by shielded sliding doors. The surgical, MR imaging, angiography, and CT tables are positioned in order of use. The patient lies on a fully MR imaging- and radiography-compatible mobile patient tabletop that is used to move the patient quickly and safely among the tables in the imaging and operating components of the MRXO suite. The authors performed all interventional procedures safely. The specially designed operating tabletop of the MRXO suite reduced the limitations on neurosurgeons during standard neurosurgical procedures. This hybrid suite helps to provide high-quality intraoperative imaging, greatly reducing the risk of unexpected events during the procedure. The MRXO suite, which combines OR and imaging equipment, represents a significant milestone in the improvement of neurosurgical diagnosis and treatment and other interventional procedures. Another advantage of the MRXO suite is its cost-effectiveness, which is partly due to its streamlined imaging procedure.

Comparison of Delayed Enhanced CT and Chemical Shift MR for Evaluating Hyperattenuating Incidental Adrenal Masses1

To retrospectively compare the accuracy of delayed enhanced computed tomography (CT) and chemical shift magnetic resonance (MR) imaging for characterizing hyperattenuating adrenal masses at CT, with either follow-up imaging or pathologic review as the reference standard. The institutional review board approved this retrospective study with a waiver of patient informed consent. Forty-three hyperattenuating adrenal masses (>10 HU) on unenhanced CT images were found in 34 patients (23 men and 11 women; mean age, 52.7 years) by reviewing radiologic reports. These lesions were retrospectively analyzed with delayed enhanced CT and chemical shift MR. The diagnostic accuracy of CT by using absolute percentage loss of enhancement (PLE) and relative PLE and of chemical shift MR by using adrenal-to-spleen ratio (ASR) or signal intensity index (SII) were obtained to determine which modality was more accurate for lipid-poor adenoma. For CT, an adenoma was diagnosed if a mass had an absolute PLE greater than 60% and a relative PLE greater than 40%. For MR, an adenoma was diagnosed if a mass had an ASR of 0.71 or an SII greater than 16.5%. McNemar test was used to compare diagnostic performance of CT and MR. Hyperattenuating adrenal masses included 37 adenomas and six nonadenomas. The sensitivity, specificity, and accuracy for adenoma at CT were 97% (36 of 37), 100% (six of six), and 98% (42 of 43), respectively, and at MR were 86% (32 of 37), 50% (three of six), and 49% (21 of 43), respectively. CT helped confirm five more adenomas and three more metastatic tumors than did MR. However, there was no significant difference for diagnostic accuracy between these two imaging modalities (P>.05) Delayed enhanced CT can characterize additional hyperattenuating adrenal masses that cannot be characterized with chemical shift MR.

Contrast-enhanced FDG-PET/CT vs. spio-enhanced MRI vs. FDG-PET vs. CT in patients with liver metastases from colorectal cancer: a prospective study with intraoperative confirmation

The choice of imaging before liver surgery is debated regarding the use of magnetic resonance (MR) imaging, computed tomography (CT), and positron emission tomography (PET). No studies have compared contrast-enhanced PET/CT with superparamagnetic iron oxide (SPIO)-enhanced MR imaging. To compare PET/CT with superparamagnetic iron oxide (SPIO)-enhanced MR imaging, PET, and CT in the detection of liver metastases (LM) and extrahepatic tumor from colorectal cancer (CRC). Thirty-five patients with suspected LM underwent PET/CT with a contrast-enhanced CT protocol and SPIO-enhanced MR imaging. Readers independently analyzed images from MR imaging, PET/CT, and the CT part and PET part of the PET/CT study. Imaging findings were compared with surgical and histological findings. Lesion-by-lesion sensitivity and accuracy for liver lesions was 54% and 77% for PET alone, 66% and 83% for PET/CT, 82% and 82% for SPIO-enhanced MR imaging, and 89% and 77% for CT alone, respectively. CT and SPIO-enhanced MR imaging were less specific but significantly more sensitive than PET (P<0.0001). For extrahepatic tumor, sensitivity and specificity was 83% and 96% for PET/CT and 58% and 87% for CT, respectively. CT and SPIO-enhanced MR imaging are more sensitive but less specific than PET in the detection of LM. PET/CT can detect more patients with extrahepatic tumor than CT alone.

CT and MR Imaging after Imaging-guided Thermal Ablation of Renal Neoplasms

In recent years, thermal tumor ablation techniques such as percutaneous radiofrequency (RF) ablation and cryoablation have assumed an important role in the management of renal tumors, particularly in patients who may be suboptimal candidates for more invasive surgical techniques. Postablation computed tomography (CT) and magnetic resonance (MR) imaging play an important part in evaluation of the ablation zone, surveillance for residual or recurrent tumor, and identification of procedure-related complications. The appearance of the ablation zone may vary depending on the ablation technique used, initial tumor size, and tumor location and composition. Most ablated tumors demonstrate a gradual decrease in size over time once the acute changes have resolved, although tumor involution is more evident after cryoablation than after RF ablation. Exophytic tumor ablation zones typically have a "bull's-eye" appearance on CT scans and MR images obtained after RF ablation, with a visible mass often persisting in the absence of viable tumor. Residual or recurrent tumor often manifests as a focus of nodular or crescentic enhancement on postablation contrast material-enhanced CT scans and MR images, although a thin peripheral rim of enhancement often persists for several months following cryoablation. Complications following renal tumor ablation are usually minor but may include hemorrhage, ureteral stricture, urine leak, colonic perforation and colonephric fistula, and pneumothorax. As more patients undergo renal ablation procedures, it will become increasingly important that radiologists be able to recognize typical postablation CT and MR imaging findings to prevent confusing them with other pathologic processes.

Post‐implant computed tomography–magnetic resonance prostate image registration using feature line parallelization and normalized mutual information

Post‐implant dosimetry for permanent prostate brachytherapy is typically performed using computed tomography (CT) images, for which the clear visualization of soft tissue structures is problematic. Registration of CT and magnetic resonance (MR) image volumes can improve the definition of all structures of interest (soft tissues, bones, and seeds) in the joint image set. In the present paper, we describe a novel two‐stage rigid‐body registration algorithm that consists of (1) parallelization of straight lines fit to image features running primarily in the superior–inferior (Z) direction, followed by (2) normalized mutual information registration. The first stage serves to fix rotation angles about the anterior–posterior (Y) and left–right (X) directions, and the second stage determines the remaining Z‐axis rotation angle and the X, Y, Z translation values. The new algorithm was applied to CT and 1.5T MR (T2‐weighted and balanced fast‐field echo sequences) axial image sets for three patients acquired four weeks after prostate brachytherapy using I125 seeds. Image features used for the stage 1 parallelization were seed trains in CT and needle tracks and seed voids in MR. Simulated datasets were also created to further investigate algorithm performance. Clinical image volumes were successfully registered using the two‐stage approach to within a root‐mean‐squares (RMS) distance of <1.5 mm, provided that some pubic bone and anterior rectum were included in the registration volume of interest and that no motion artifact was apparent. This level of accuracy is comparable to that obtained for the same clinical datasets using the Procrustes algorithm. Unlike Procrustes, the new algorithm can be almost fully automated, and hence we conclude that its further development for application in post‐implant dosimetry is warranted.PACS numbers: 87.53.Jw, 87.57.Gg, 87.59.Fm, 87.61.Pk

Comparison of computed tomography and magnetic resonance based target volume in brain tumors

This study was mainly framed to study the difference in tumor volumes as seen on computed tomography (CT) and magnetic resonance (MR) and their significance in planning. Twenty-five patients with brain tumor of different diagnoses who underwent stereotactic radiotherapy were included in this study. CT and MR imaging was done for all the patients with 2.5 mm slice thickness. The CT tumor volume and MR tumor volume were measured and compared with each other. The center of mass (CM) of the tumor volume delineated on CT and MR were computed and the shift between the two CMs was determined. The mean and median volume of the tumor as measured from MR scans was 19.67 cc +/- 13.73 and 16.13 cc (range: 3.25 cc-50.37 cc). Similarly, the mean and median volume of the tumor as measured from CT scans was 15.05 cc +/- 10.13 and 11.63 cc (range: 3.0 cc-36.25 cc) respectively. The mean and median CM shift between CT and MR was 5.47 mm and 5.21 mm respectively. The study demonstrates that MR is an indispensable imaging modality in radiotherapy for planning brain tumors.

Treatment of arteriovenous malformations with linear accelerator–based radiosurgery compared with Gamma Knife surgery

The authors sought to compare the outcomes of patients with arteriovenous malformations (AVMs) treated by Gamma Knife surgery (GKS) with those of patients treated by linear accelerator-based (LINAC) radiosurgery. One hundred and eighty-seven patients with AVMs were treated at our institution between 1992 and 2003. Ninety-one patients were treated with GKS and 96 patients were treated with LINAC radiosurgery. Patient and treatment characteristics in the two groups included the following. In the LINAC group, the median age was 33 years (range 9-66 years); the median dose was 16 Gy (70% isodose line); the median treated AVM volume was 5.5 cm3; and 46% of patients in this group were treated after hemorrhage. In the GKS group, the median age was 38 years (range 6-63 years); the median dose was 20 Gy (50% isodose line); the median treated AVM volume was 4.3 cm3; and 44% of patients in this group were treated after hemorrhage. Obliteration of AVMs was determined by performing computed tomography (CT) angiography and/or magnetic resonance (MR) angiography and angiography. Patient follow-up evaluation included obtaining an MR angiogram/MR image or CT angiogram at 6 months, at 1 year, and then annually thereafter. Angiography was performed to confirm obliteration when MR angiography and/or CT angiography no longer revealed evidence of an AVM. The 5-year estimated AVM obliteration rate was 66% in the entire patient group; the LINAC group was 60%; the GKS group was 72%; this difference was not statistically significant (p = 0.97). Twelve patients who underwent treatment with LINAC radiosurgery underwent retreatment with GKS and one was retreated with LINAC radiosurgery. The obliteration rate was 82%. Six patients treated with GKS were retreated with GKS, but the follow-up time is of short duration. Chronic toxicity occurred in 8% of both the GKS and the LINAC groups (p = 0.61). Posttreatment hemorrhage during the time of risk before AVM obliteration was 13% in the GKS group and 6.2% in the LINAC group (p = 0.05). Treatment of patients with AVMs by using LINAC radiosurgery and GKS treatment produces high obliteration rates with acceptable long-term radiation toxicity in the patients treated.

Contemporary adrenal scintigraphy

High-resolution computed tomography (CT) and magnetic resonance (MR) imaging have replaced scintigraphy as primary imaging modalities for the evaluation of adrenal diseases. Thin-slice CT, CT contrast washout studies and MR pulse sequences specifically designed to identify adrenal lipid content have radically changed the approach to anatomic imaging and provide unique insight into the physical characteristics of the adrenals. With a confirmed biochemical diagnosis, further evaluation is often unnecessary, especially in diagnostic localization of diseases of the adrenal cortex. However, despite the exquisite detail afforded by anatomy-based imaging, there are not infrequently clinical situations in which the functional insight provided by scintigraphy is crucial to identify adrenal dysfunction and to assist in localization of adrenocortical and adrenomedullary disease. The introduction of hybrid PET/CT and SPECT/CT, modalities that directly integrate anatomic and functional information, redefine the radiotracer principle in the larger context of high-resolution anatomic imaging. Instead of becoming obsolete, scintigraphy is an element of a device that combines it with CT or MR to allow a direct correlation between function and anatomy, whereby the combination creates a more powerful diagnostic tool than the separate component modalities.

MR Angiography and CT Angiography of the Artery of Adamkiewicz: State of the Art

It is very important to assess the artery of Adamkiewicz before repair of the thoracoabdominal or descending thoracic aorta. Several studies have demonstrated the feasibility and advantages of noninvasive assessment of the artery of Adamkiewicz with magnetic resonance (MR) angiography and multi-detector row computed tomographic (CT) angiography. Recent advances in MR angiography and CT angiography have led to changes in the detectability of this artery. In the present study, both MR angiography and CT angiography were performed without complications for preoperative evaluation of 30 patients who underwent repair of the thoracoabdominal or descending thoracic aorta. MR angiography provided detection rates as high as 93% and 80% with the morphologic "hairpin turn" criterion and the anatomic "continuity" criterion, respectively. Sixteen-detector row CT angiography provided detection rates as high as 83% and 60%, respectively. Use of both MR angiography and CT angiography provided higher detection rates of 97% and 90%, respectively. The collateral pathways were depicted in seven cases (23%). MR angiography is superior for depiction of the artery of Adamkiewicz, especially when it arises from the false lumen of a dissecting aneurysm. CT angiography has a wide field of view and allows depiction of significant collateral pathways associated with the internal thoracic artery and intercostal arteries.