Biomedical subjects

K Farahani

Publications and source records attributed to K Farahani.

At least 19 recordsLinked to original sources

PubMed2000

Safety of MRI-guided endovascular guidewire applications.

Magnetic radiofrequency (RF) fields applied during magnetic resonance imaging (MRI) may induce heating in devices made from conductive materials. The present paper reports on theoretical and experimental studies on the RF heating resonance phenomenon of an endovascular guidewire. A nitinol-based guidewire was inserted into a vessel phantom and imaged at 1.5 and 0.2 T with continuous temperature monitoring at the guidewire tip. The heating effects due to different experimental settings were examined. A model is developed for the resonant current and the associated electric field produced by the guidewire acting as an antenna. Temperature increases of up to 17 degrees C were measured while imaging the guidewire at an off-center position in the 1.5 T MR system. Power absorption produced by the resonating wire decreased as the repetition time was increased. No temperature rise was measured at 0.2 T. Considering the potential utility of low-field, open MR systems for MRI-guided endovascular interventions, it is important to be aware of the safety of such applications.

Blood Vessels↗

PubMed2000

Magnetic resonance imaging-guided neurosurgery in the magnetic fringe fields: the next step in neuronavigation.

OBJECTIVE: We describe the development of an alternative approach to intraoperative magnetic resonance imaging (iMR)-guided neurosurgery and report our initial experience with 22 craniotomies and 16 brain biopsies. The advantages and disadvantages of each approach are examined. METHODS: An iMR suite houses a 0.2-T open configuration system (Siemens Medical Systems, Erlangen, Germany) and is equipped with anesthetic gases and a magnetic resonance imaging (MRI)-compatible anesthesia machine and monitor. Standard operating instruments and equipment were tested for safety and compatibility in the magnetic fringe fields surrounding the open MRI system. We then performed brain biopsies and craniotomies in the iMR suite. RESULTS: Standard operating equipment functioned properly in the 0.5- to 10-mT zone and was not affected by the magnet's attractive force. Twenty-two craniotomies and 16 brain biopsies were performed in the interventional suite, using serial intraoperative MRI guidance, without injury to patients or operating room staff. CONCLUSION: Full neurosurgical procedures may be performed in the weak fringe fields surrounding an MRI system, using standard operating room equipment. This approach to iMR-guided neurosurgery offers a significant cost advantage over retrofitting an entire operative suite with "MRI-compatible" surgical equipment. The surgeon's familiarity with standard equipment and the reliability of the equipment are additional advantages. Neurosurgery in the fringe fields allows the neurosurgeon to utilize serial MRI with a minimum of inconvenience, disruption, and change to the standard neurosurgical procedure. Serial intraoperative imaging to visualize the changes in the brain that are associated with neurosurgical intervention seems to enhance the ability to safely and effectively accomplish neurosurgical goals.

Adolescent↗

PubMed1999

Contemporaneous positron emission tomography and MR imaging at 1.5 T.

Simultaneous acquisition of positron emission tomography (PET) and magnetic resonance (MR) images using an MR-compatible PET system will obviate the need for image registration and will allow unique studies of structure and function of living organisms in one setting. Here we report on simultaneous acquisition of PET and MR images on a clinical 1.5 T system using a 54 mm diameter prototype MR-compatible PET system (McPET). Phantom experiments were performed in order to determine the effect of the McPET system on MR images. The results demonstrated the system to be fully MR compatible, in both its detector head construction and operation. The McPET construction offers a promising method for design of a large-scale MR-compatible PET system that will be useful in functional studies of the brain.

Artifacts↗

PubMed1999

Teleradiology in the operating room of the future.

Recent advances in magnetic resonance imaging (MRI) are rapidly making this modality the imaging method of choice for image-guided neurosurgical operations. However, to be ready for its prime time in the operating room (OR), utilization of MRI in the OR requires development of better techniques for image-guided navigation, as well as interactive real-time teleradiologic methods that will allow tele-collaboration between the surgeon and the radiologist. This presentation describes our work in progress toward achievement of teleradiology in the OR.

Computer Systems↗

PubMed1999

MRI of thermally denatured blood: methemoglobin formation and relaxation effects.

Focal regions of T1-shortening have been observed in magnetic resonance imaging (MRI)-monitored thermal ablations of perfused tissues. The aims of this study were two-fold: to find evidence for heat-induced conversion of hemoglobin (Hb) to methemoglobin (mHb), and to investigate the effects of heat treatment of in-vitro blood components upon their MR relaxation times. Spectrophotometric studies were performed to confirm the heat-induced formation of methemoglobin. Preparations of whole and fractionated blood, previously submitted to elevated temperatures of 40 degrees C to 80 degrees C, were imaged and the relaxation times were calculated. Optical absorption spectra of samples containing free Hb, heated to 60 degrees C, showed increased light absorption at 630 nm, evident of mHb presence. Short T1 values in whole blood (1.13 s) and packed red blood cell (0.65 s) compartments, heated at 60 degrees C, compared to their baseline values (1.62 s and 0.83 s, respectively), were attributed to mHb formation. In relation to MRI-guided thermal interventions, these results suggest a possible explanation for observation of hyperintense regions on T1-weighted images.

Animals↗

PubMed1999

A study of artefacts in simultaneous PET and MR imaging using a prototype MR compatible PET scanner.

We have assessed the possibility of artefacts that can arise in attempting to perform simultaneous positron emission tomography (PET) and magnetic resonance imaging (MRI) using a small prototype MR compatible PET scanner (McPET). In these experiments, we examine MR images for any major artefacts or loss in image quality due to inhomogeneities in the magnetic field, radiofrequency interference or susceptibility effects caused by operation of the PET system inside the MR scanner. In addition, possible artefacts in the PET images caused by the static and time-varying magnetic fields or radiofrequency interference from the MR system were investigated. Biological tissue and a T2-weighted spin echo sequence were used to examine susceptibility artefacts due to components of the McPET scanner (scintillator, optical fibres) situated in the MR field of view. A range of commonly used MR pulse sequences was studied while acquiring PET data to look for possible artefacts in either the PET or MR images. Other than a small loss in signal-to-noise using gradient echo sequences, there was no significant interaction between the two imaging systems. Simultaneous PET and MR imaging of simple phantoms was also carried out in different MR systems with field strengths ranging from 0.2 to 4.7 T. The results of these studies demonstrate that it is possible to acquire PET and MR images simultaneously, without any significant artefacts or loss in image quality, using our prototype MR compatible PET scanner.

Artifacts↗

PubMed1999

Intra-arterial Cereport (RMP-7) and carboplatin: a dose escalation study for recurrent malignant gliomas.

OBJECTIVE: Animal and human studies have shown increased delivery of radiolabeled compounds across the blood-brain-tumor barrier using intra-arterial (IA) Cereport (RMP-7; Alkermes Inc., Cambridge, MA) with a radiolabeled tracer. This present study assesses the safety, tolerance, and preliminary efficacy of the IA administration of carboplatin with Cereport. METHODS: An open-label dose escalation study of IA Cereport (10-300 ng/kg) with 100 mg of IA carboplatin was conducted in 11 patients with recurrent malignant gliomas and 1 patient treated adjuvantly after radiation therapy. Tumor size and laboratory and clinical statuses were assessed. RESULTS: Adverse events were mainly neurological in nature and corresponded to the anatomic location of the tumor. Karnofsky performance scale scores did not decline, overall, for those patients who had tumor response. Tumor shrinkage was observed in three of six evaluable patients who received a dose of 300 ng/kg with durable responses of 60, 64, and 106+ weeks. CONCLUSION: Previous studies have demonstrated increased permeability in human gliomas using IA Cereport. This study demonstrates durable imaging responses using 100 mg of IA carboplatin in combination with Cereport. The drug combination in this patient population seems to be safe and acceptable, providing a novel means of antitumor dose intensification.

Adult↗

PubMed1997

Simultaneous PET and MR imaging.

We have developed a prototype PET detector which is compatible with a clinical MRI system to provide simultaneous PET and MR imaging. This single-slice PET system consists of 48 2 x 2 x 10 mm3 LSO crystals in a 38 mm diameter ring configuration that can be placed inside the receiver coil of the MRI system, coupled to three multi-channel photomultipliers housed outside the main magnetic field via 4 m long and 2 mm diameter optical fibres. The PET system exhibits 2 mm spatial resolution, 41% energy resolution at 511 keV and 20 ns timing resolution. Simultaneous PET and MR phantom images were successfully acquired.

Equipment Design↗

PubMed1997

Biopsy of hepatic dome lesions: semi-real-time coronal MR guidance technique.

OBJECTIVE: MR imaging, with its coronal imaging capability, may be ideally suited for biopsies of hepatic dome lesions. We are reporting on the successful semi-real-time biopsy of such lesions using a 0.2-T open-configuration MR scanner in five patients. CONCLUSION: MR guidance holds promise for facilitating biopsies of hepatic dome masses.

Adult↗

PubMed1997

Intracarotid infusion of RMP-7, a bradykinin analog, and transport of gallium-68 ethylenediamine tetraacetic acid into human gliomas.

The bradykinin analog, RMP-7, was investigated for its ability to increase selectively the transport of 68Ga ethylenediamine tetraacetic acid (EDTA) into recurrent malignant gliomas in nine patients. For each patient, two position emission tomography (PET) studies (one with and one without RMP-7) were performed. For studies with RMP-7, 10 to 300 ng/kg of the compound was infused into the supraophthalmic carotid artery over 15 minutes. In each PET study, a sequence of PET scans was initiated simultaneously with an intravenous bolus of 68Ga EDTA (5-10 mCi). Arterial samples were taken to provide the input function. All PET scans were coregistered to the magnetic resonance (MR) images of the patient. Regions of interest were defined for tumor and normal tissue regions on MR images and were copied to the coregistered PET dynamic images to provide brain tissue-time activity curves. The constant (Ki) for the transport of gallium-68 from plasma to brain tissue was determined using a simple compartmental model. Intracarotid infusion of RMP-7 significantly increased transport into tumor regions with an average increase of 46 +/- 42% (mean +/- standard deviation, p < 0.05). Permeability in normal tissue regions was not significantly increased. Tumors in three of six patients treated with 300 ng/kg RMP-7 and carboplatin had at least a 50% reduction in tumor volume as measured by MR imaging. Intracarotid infusion of RMP-7 is a novel technique for selective delivery of antitumor compounds into brain tumors.

Adult↗

PubMed1997

Frequency-selective fat suppression MR imaging. Localized asymmetric failure of fat suppression mimicking orbital disease.

Our objectives were to further characterize an artifact related to the localized failure of the frequency-selective (FATSAT) fat suppression magnetic resonance (MR) imaging technique. We constructed two phantoms simulating human orbital anatomy and imaged them on a 1.5-T MR scanner using (FATSAT) and short T1 inversion recovery (STIR) techniques of fat suppression. The first phantom resembled orbit structural configurations; it was imaged in coronal and axial planes and in varying orientations with respect to the main magnetic field (Z axis) to study the features of the artifact and to reproduce the asymmetry seen in clinical cases. We designed the second phantom to enable quantification of the change in artifact size with change in orientation. We imaged the orbits of a normal human volunteer in similar planes and orientations, and compared the results to clinical cases demonstrating the artifact and true orbital disease. The artifact identified with localized failure of FATSAT fat suppression manifested as regions of hyperintensity maximal at fat-air interfaces, with gradual fading of the increased signal with distance from the interfaces. The artifact was most prominent when the interfaces were perpendicular to the axis of the main magnetic field (Z axis). The regions of increased brightness obscured normal orbital structures but were not associated with alterations in the geometry of these structures. Changes in orientation of the interfaces with respect to the Z axis, both in the phantoms and normal volunteer, reproduced the asymmetry of fat suppression failure seen in clinical cases. The relationship of size of the artifact to change in orientation was non-linear. The artifact was not seen on STIR images. We concluded that failure of FATSAT fat suppression may mimic orbital disease, particularly if asymmetric. As predicted by the Maxwell electromagnetism equation, slight variations in orientation of the fat-air interface to the Z axis may produce large asymmetries in fat suppression failure in the orbit. Confirmation may require either comparison with additional pulse sequences [T1-weighted spin echo (T1W SE) or STIR] or repositioning the patient's head to check for persistence of the finding with varying orientations.

Adipose Tissue↗

PubMed1996

Magnetic resonance imaging of plantar plate rupture.

Degenerative plantar plate failure is an under-recognized cause of lesser metatarsalgia. We performed magnetic resonance imaging (MRI) with a small receiver coil in 13 patients in whom plantar plate ruptures of the second or third metatarsophalangeal joint were clinically suspected. In eight patients, MRI showed focal hyperintensity in the plantar plate that was interpreted as a rupture of the plate. Ruptures were confirmed in all five patients who underwent an operative procedure to treat the unstable, painful metatarsophalangeal joint. MRI is a noninvasive technique that can visualize plantar plate abnormalities and aid the clinical evaluation of problematic lesser metatarsalgia.

Aged↗

PubMed1996

Interventional magnetic resonance imaging of the head and neck and new imaging techniques.

The use of magnetic resonance imaging to directly guide therapy is a new area of investigation. Clinical magnetic resonance imaging has the potential to evolve from a purely diagnostic tool into a guide for invasive procedures. The idea of using magnetic resonance to guide percutaneous biopsy developed one decade ago. Magnetic resonance-guided fine-needle aspiration for head and neck lesions has become a standard technique some institutions. Once the needle reaches a lesion in the head and neck, it is natural to explore the possibility of treatment in the same setting. The concept of interventional magnetic resonance imaging has generated interest among radiologists, surgeons, and manufacturers. This article provides an overview of interventional procedures of the head and neck and other new imaging techniques that have been developed.

Head and Neck Neoplasms↗

PubMed1995

Hyperacute thermal lesions: MR imaging evaluation of development in the brain.

PURPOSE: To determine the natural time course of development of hyperacute thermal lesions in the brain. MATERIALS AND METHODS: Ten interstitial lesions were created in five rabbit brains with a radio-frequency probe; an electrode-tip temperature of 80 degrees C was maintained for 60 seconds. Continuous fast spin-echo magnetic resonance (MR) imaging was used to follow lesion development for a minimum of 30 minutes. Temporal variations in lesion size and signal intensity were examined. Findings in final images were correlated with histologic findings. RESULTS: Images demonstrated a focal hyperintense zone, which developed into an expanding ring of edema surrounding a necrotic center in about 10 minutes. Quantitative analysis revealed a 23% +/- 6 (standard deviation) increase in average signal intensity of the edema layer and a 152% +/- 41 increase in overall lesion size. CONCLUSION: Full development of a thermal lesion is delayed for a period of minutes. Clinical implications of this effect should be considered when MR imaging-guided thermal ablation is performed.

Animals↗

PubMed1995

Early postoperative appearance of radiofrequency lesions on magnetic resonance imaging.

Eleven patients who underwent stereotactic radiofrequency lesions in the central nervous system had magnetic resonance imaging follow-up within 72 hours of surgery to determine the early appearance of their lesions. Eight patients with severe tremor, one with chronic pain, and two with dystonia were analyzed. There were six female patients and five male patients, age 7 to 75 years (mean +/- standard deviation = 42 +/- 21). Magnetic resonance imaging was performed postoperatively at 32 +/- 25 hours (range, 3-72). Postoperative T1-weighted spin echo images demonstrated foci of iso- to hyperintensity surrounded by an edge of hypointensity, and corresponding T2-weighted images showed a lesion with three concentric zones consisting of inner hypointense, middle hyperintense, and outer hypointense zones. Gadolinium increased T1-weighted image lesion visibility, and a ring of enhancement around the zone of hypointensity was observed. Lesions could be seen as early as 3 hours after surgery. The lesions were best shown on gadolinium-enhanced T1-weighted images and on T2-weighted images. The edema surrounding the lesion increased over time, up to the 72 hours studied. These data provide important information on the development of lesion appearance, which may be applied in the development of real-time magnetic resonance imaging monitoring of radiofrequency lesion formation. This technique associated with electrophysiological response and the real-time visualization of the anatomic correlation of the probe may allow for a very precise and selected lesion in the central nervous system for the treatment of functional disorders and brain tumors.

Adolescent↗

PubMed1995

Dynamic MRI-guided interstitial laser therapy: a new technique for minimally invasive surgery.

Interstitial laser therapy (ILT) is a promising therapeutic technique in which laser energy is delivered percutaneously to various depths in tissue. In this study, the authors compared high-speed magnetic resonance imaging (MRI) of ILT in tissues during treatment with post-treatment histopathologic specimens. The use of 5-second MRI scans allowed detection of thermal damage by the 1064-nm neodymium:yttrium-aluminum-garnet laser in ex vivo liver and brain tissues. These tissues were treated by ILT with 20 W of laser output for 5 to 30 seconds via a 600-microns fiberoptic inserted 1 cm into the specimens at a power density of 7 kW/cm2 at the tip of the bare fiber. Sequential MRI measurements of lesion areas made during and after treatment were compared to measurements of laser-induced tissue damage in histopathologic sections. Fast MRI scans and tissue histology both demonstrated increased lesion size with time of ILT. Serial images obtained during ILT detected thermal changes as areas of low signal intensity that exceeded the size of the post-treatment lesions as measured on either final MRI or histology. The thermal effects detectable by these high-speed MRI sequences can be used to monitor laser-induced tissue changes during therapy, thereby providing a valuable noninvasive method for the intraoperative assessment of heat distribution during ILT.

Animals↗

PubMed1995

Preliminary experience with MR-guided thermal ablation of brain tumors.

PURPOSE: To evaluate the feasibility of a technique of MR-guided stereotactic radio frequency ablation, which was developed as a minimally invasive treatment for brain tumors, and to determine MR characteristics and sequential evolution of radio frequency lesions created to ablate brain tumors. METHODS: Fourteen lesions in 12 patients with primary and metastatic brain tumors were treated with this technique and followed for up to 10 months. The stereotactic coordinates of the tumor and the angle of the radio frequency probe were calculated on MR imaging. The radio frequency lesion was generated in the awake patient by increasing the temperature to 80 degrees C within the tumor for 1 minute. This was repeated until the entire tumor volume was destroyed. MR imaging was performed before, during, and immediately after the radio frequency procedure, and sequential MR was obtained during clinical follow-up. RESULTS: MR imaging clearly showed well-defined radio frequency lesions and provided feedback for treatment planning. The radio frequency lesion boundary was well identified as a dark signal rim on T2-weighted images and showed ring enhancement on contrast-enhanced T1-weighted images. The sequential MR imaging showed the radio frequency lesions decreased in volume in all cases, suggesting focal control. CONCLUSION: Stereotactic MR-guided radio frequency brain tumor ablation is a feasible and promising technique that can be an attractive brain tumor treatment alternative. MR provided not only accurate tumor location but also visualization of feedback of thermal tissue changes that reflected therapeutic effect.

Adenocarcinoma↗

PubMed1994

Plantar plate of the foot: findings on conventional arthrography and MR imaging.

The plantar plate of the foot is formed by the plantar aponeurosis and plantar capsule. The plantar plate arises from the distal plantar aspect of the metatarsal neck and inserts on the plantar aspect of the proximal phalangeal base. This thick plate supports the undersurface of the metatarsal head and resists hyperextension of the metatarsophalangeal joint (MTPJ) [1]. Plantar plate rupture may present as lesser metatarsalgia (the lesser metatarsals are the second through fifth), occasionally with exuberant synovitis. Plantar plate derangement also plays a central role in the genesis of the common hammertoe [2, 3]. Rupture or degeneration of the plantar plate destabilizes the MTPJ, allowing dorsal subluxation of the proximal phalanx. The resulting "cock-up" deformity at the MTPJ shortens and compromises the action of the extensor digitorum longus tendon, contributing over time to a flexion deformity at the interphalangeal joints.

Adult↗