Biomedical subjects

M A Moerland

Publications and source records attributed to M A Moerland.

18 recordsLinked to original sources

PubMed2006

Development of a tapping device: a new needle insertion method for prostate brachytherapy.

The purpose of this study is to develop and test a tapping device for needle insertion for prostate brachytherapy. This device will tap the needle into the prostate with a certain, well-defined, amount of momentum, instead of the currently used method of pushing the needle. Because of the high needle insertion velocity, we expect prostate motion and deformation to be less compared to current methods. We measured the momentum that is applied when manually tapping the needle into the prostate and found a mean momentum of 0.50 +/- 0.07 N s. The tapping device is pneumatically driven and we found that the delivered momentum increased linearly with the applied air pressure. The efficacy of the tapping device was tested on a piece of beef, placed on a freely moving and rotating platform. A significant correlation was found between the applied pressure and the rotation and displacement of the beef. Displacements and rotations were minimal for the highest pressure (4 bar) and amounted to only 2 mm and 6 degrees, respectively. Higher air pressures will further reduce displacements and rotations.

Brachytherapy↗

PubMed2001

Quantitative dose-volume response analysis of changes in parotid gland function after radiotherapy in the head-and-neck region.

PURPOSE: To study the radiation tolerance of the parotid glands as a function of dose and volume irradiated. METHODS AND MATERIALS: One hundred eight patients treated with primary or postoperative radiotherapy for various malignancies in the head-and-neck region were prospectively evaluated. Stimulated parotid flow rate was measured before radiotherapy and 6 weeks, 6 months, and 1 year after radiotherapy. Parotid gland dose-volume histograms were derived from CT-based treatment planning. The normal tissue complication probability model proposed by Lyman was fit to the data. A complication was defined as stimulated parotid flow rate <25% of the preradiotherapy flow rate. RESULTS: The mean stimulated preradiotherapy flow rate of 174 parotid glands was 0.34 mL/min. The mean flow rate reduced to 0.12 mL/min 6 weeks postradiotherapy, but recovered to a mean flow rate of 0.20 mL/min at 1 year after radiotherapy. Reduction in postradiotherapy flow rate correlated significantly with mean parotid dose. No threshold dose was found. Increasing the irradiated volume of parotid glands from 0%-40% to 90-100% in patients with a mean parotid dose of 35-45 Gy resulted in a decrease in flow ratio from, respectively, approximately 100% to less than 10% 6 weeks after radiation. The flow ratio of the 90%-100% group partially recovered to 15% at 6 months and to 30% at 1 year after radiotherapy. The normal tissue complication probability model parameter TD(50) (the dose to the whole organ leading to a complication probability of 50%) was found to be 31, 35, and 39 Gy at 6 weeks, 6 months, and 1 year postradiotherapy, respectively. The volume dependency parameter n was around 1, which means that the mean parotid dose correlates best with the observed complications. There was no steep dose-response curve (m = 0.45 at 1 year postradiotherapy). CONCLUSIONS: This study on dose/volume/parotid gland function relationships revealed a linear correlation between postradiotherapy flow ratio and parotid gland dose and a strong volume dependency. No threshold dose was found. Recovery of parotid gland function was shown at 6 months and 1 year after radiotherapy. In radiation planning, attempts should be made to achieve a mean parotid gland dose at least below 39 Gy (leading to a complication probability of 50%).

Adult↗

PubMed2000

CT-based parotid gland location: implications for preservation of parotid function.

PURPOSE: The position of the parotid gland in relation to surrounding structures was investigated. MATERIALS AND METHODS: Sixty-five patients with head and neck tumours were prospectively evaluated. Parotid position was determined using beam's eye views of CT images projected on simulator films. Distances between the different borders of the parotid gland and surrounding bony marks were quantitatively assessed. RESULTS: The parotid gland volume ranged from 12.9 to 46.4 cm(3). The distance between the cranial border of the parotid gland and the tuberculum anterior of the atlas ranged between 0.7 and 4.8 cm. The position of the parotid gland was unaffected by the angle of the mandible. CONCLUSIONS: The size and position of the parotid gland varies largely among patients. As the extent of radiation-induced salivary dysfunction depends on the volume of the gland tissue exposed, CT-based simulation of radiation fields is necessary.

Head and Neck Neoplasms↗

PubMed2000

The combined use of the natural and the cumulative dose-volume histograms in planning and evaluation of permanent prostatic seed implants.

BACKGROUND AND PURPOSE: To investigate prostate dose coverage and overdosage in planned and realized permanent iodine seed prostate implants and to explore the use of the natural dose-volume histogram (NDVH) and the cumulative dose-volume histogram (CDVH) as tools to optimize prostate implants. MATERIALS AND METHODS: The optimal prescription dose (PD) or natural prescription dose (NPD) was derived from the NDVH. The mismatch between the NPD and the given PD was called the natural dose ratio (NDR). For an ideal implant the NDR should be 1. The target is overdosed if NDR >1 and underdosed if NDR <1. The NDR and prostate coverage were evaluated in implants of nine patients. Prostate coverage was determined from the CDVH based on pre-implant ultrasound or post-implant MRI for the planned and realized implants, respectively. The use of the NDVH to further optimize the planned prostate implants was also explored. RESULTS: The mean values of the NDRs were 1.30+/-0.34 (range 0.76-1.79), 1.22+/-0.31 (0.76-1.74) and 1.22+/-0.12 (0.98-1.33) for the planned, realized and optimized seed distributions, respectively. The realized prostatic implants showed smaller prostate coverage than the planned implants. The prostate volume fractions receiving 100% of the prescription dose were V(100)=79+/-6% and V(100)=97+/-3% for the realized and the planned implants, respectively. CONCLUSIONS: The NDVH and the CDVH proved to be valuable tools in plan evaluation. The NDVH and its derived parameter NDR quantify the risk of under or overdosage for a given PD. The CDVH is valuable in evaluation of prostate coverage realized prostate. Our strategy to implant just the prostate and not the prostate plus a margin led to NDR values between 1.1 and 1.3 and a prostate coverage of V(100)=79+/-6% in the nine patients. The planned coverage of V(100)=95% was not realized, mainly due to inadequate coverage of the base of the prostate.

Brachytherapy↗

PubMed1997

Evaluation of permanent I-125 prostate implants using radiography and magnetic resonance imaging.

PURPOSE: The aim of this study is the evaluation of permanent I-125 prostate implants using radiography and magnetic resonance imaging (MRI). METHODS AND MATERIALS: Twenty-one patients underwent radiography on the simulator and MRI within 3 days after implantation of the I-125 seeds. Isocentric radiographs were used for reconstruction of the seed distribution, after which registration with the seed-induced signal voids on MRI provided the seed positions in relation to the prostate. The prostate was contoured on the transversal magnetic resonance images, and dose-volume histograms were computed to evaluate the implants. The validity of the ellipsoidal prostate volume approximation, as applied in preimplant dose calculation, was assessed by comparison of ellipsoidal volumes given by prostate width, height, and length and prostate volumes obtained by a slice-by-slice contouring method, both on postimplant MRI. Prostate volume changes due to postimplant prostate swelling were assessed from radiographs taken at 3 days and 1 month after the implantation. RESULTS: The seeds were readily identified on T1-weighted spin-echo images and matched with the seed distribution reconstructed from the isocentric radiographs. The matching error, averaged over 21 patients, amounted to 1.8 +/- 0.4 mm (mean +/- standard deviation). The fractions of the prostate volumes receiving the prescribed matched peripheral dose (MPD) ranged from 32 to 71% (mean +/- standard deviation: 60 +/- 10%). Prostate volumes, obtained by the contouring method on postimplant MRI, were a factor 1.5 +/- 0.3 larger than the ellipsoidal volumes given by the prostate dimensions on postimplant MRI. Prostate volumes 3 days after the implantation were a factor 1.3 +/- 0.2 larger than the prostate volumes 1 month after the implantation. Registration of the reconstructed seed distribution and the MR images showed inaccuracies in seed placement, for example, two or more seeds clustering together or seeds outside the prostate. CONCLUSIONS: Registration of the reconstructed seed distribution and the MR images enabled evaluation of target coverage, which amounted to 60 +/- 10%. The discrepancy between prescribed dose and realized dose was caused by underestimation of the preimplant prostate volume due to the ellipsoidal approximation, postimplant prostate swelling at the time of evaluation, and inaccuracies in seed placement.

Brachytherapy↗

PubMed1997

A conformation number to quantify the degree of conformality in brachytherapy and external beam irradiation: application to the prostate.

PURPOSE: This article presents a method of quantitative assessment of the degree of conformality and its designation by a single numerical value. METHODS AND MATERIALS: A conformation number is introduced to evaluate objectively the degree of conformality. A comparison is made between the conformation number as found for external beam treatment plans and ultrasonically guided 125I seed implants for localized prostate cancer. RESULTS: The conformation number in case of a planning target volume irradiated with two opposed open beams, three open beams, and three beams with customized blocks amounted to 0.17, 0.39, and 0.65, respectively. The conformation number as found for ultrasonically guided permanent prostate implants using 125I seeds averaged 0.72. CONCLUSIONS: The conformation number is a convenient instrument for indicating the degree of conformality by a single numerical value. Treatments with a conformation number greater than 0.60 might be termed conformal radiotherapy.

Brachytherapy↗

PubMed1995

Analysis and correction of geometric distortions in 1.5 T magnetic resonance images for use in radiotherapy treatment planning.

The aim of this study is to investigate and correct for machine- and object-related distortions in magnetic resonance images for use in radiotherapy treatment planning. Patients with brain tumours underwent magnetic resonance imaging (MRI) in the radiotherapy position with the head fixed by a plastic cast in a Perspex localization frame. The imaging experiments were performed on a 1.5 T whole body MRI scanner with 3 mT m-1 maximum gradient capability. Image distortions, caused by static magnetic field inhomogeneity, were studied by varying the direction of the read-out gradient. For purposes of accuracy assessment, external and internal landmarks were indicated. Tubes attached to the cast and in the localization frame served as external landmarks. In the midsagittal plane the brain-sinus sphenoidalis interface, the pituitary gland-sinus sphenoidalis interface, the sphenoid bone and the corpora of the cervical vertebra served as internal landmarks. Landmark displacements as observed in the reversed read-out gradient experiments were analysed with respect to the contributions of machine-related static magnetic field inhomogeneity and susceptibility and chemical shift artifacts. The machine-related static magnetic field inhomogeneity in the midsagittal plane was determined from measurements on a grid phantom. Distortions due to chemical shift effects were estimated for bone marrow containing structures such as the sphenoid bone and the corpora of the cervical vertebra using the values obtained from the literature. Susceptibility-induced magnetic field perturbations are caused by the patient and the localization frame. Magnetic field perturbations were calculated for a typical patient dataset.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain↗

PubMed1994

The influence of respiration induced motion of the kidneys on the accuracy of radiotherapy treatment planning, a magnetic resonance imaging study.

An MRI study has been performed to determine the respiration induced motion of the kidneys. Under normal respiration conditions displacements of the left and right kidney varied from 2 to 24 mm and 4 to 35 mm, respectively. Under forced respiration conditions displacements were larger and ranged from 10 to 66 mm for the left kidney and 10 to 86 mm for the right kidney. The influence of kidney motion on the radiation dose was determined for patients irradiated on the total abdomen for ovarian cancer with shielding of the kidneys during part of the treatment. The kidney motion resulted in a larger fraction of the kidney volume receiving a dose between 20 and 22 Gy.

Adult↗

PubMed1994

Simulation of susceptibility artifacts in 2D and 3D Fourier transform spin-echo and gradient-echo magnetic resonance imaging.

A method is presented for simulating susceptibility artifacts in 2D and 3D spin-echo and gradient-echo imaging of arbitrary susceptibility distributions. The method incorporates object induced field perturbations in the time domain (k-space) and is demonstrated for spherical nonuniformities in susceptibility. Both simulations and experimental results for multi-slice 2D and 3D imaging of phantoms and human subjects are provided.

Artifacts↗

PubMed1994

Numerical analysis of the magnetic field for arbitrary magnetic susceptibility distributions in 3D.

This paper demonstrates a method to calculate the magnetic field distribution in and around a 3D object when it is magnetized by a strong homogeneous magnetic field. The numerical technique is based on the explicit finite difference method. The calculation method is validated against analytical solutions for a sphere. As an application cylinders with different ratios of lengths and diameter are studied.

Magnetic Resonance Imaging↗

PubMed1993

Susceptibility artifacts in 2DFT spin-echo and gradient-echo imaging: the cylinder model revisited.

Susceptibility-induced geometry and intensity distortions are a familiar observation in MR imaging. In the past few years several attempts have been made to aid in the understanding of susceptibility artifacts by means of simulation studies. Although these studies, which were mostly carried out with simple test objects, have produced some qualitative insight into chi-artifacts, the results lacked precision in describing finer details. In this paper we show the discrepancy between theory and experiment in previous work to be the result of an inadequate theoretical approach. In most studies so far, delta B0 effects are taken into account in the frequency domain, that is, after Fourier transformation of the data. In our view the simulation should follow the actual sequence of events in an imaging experiment and deal with the effect of error fields in the time domain (k-space) already. The correctness of this view is demonstrated here by comparing the results of time and frequency domain simulation against experimental observation for a coaxial cylinder phantom, a widely used model in this type of work. Having established the superiority of the time domain simulation, we demonstrate its use in predicting chi-artifacts under various experimental conditions, for example, in spin-echo and gradient-echo imaging with a reduced number of phase-encoding steps.

Artifacts↗

PubMed1993

Brain tumor delineation based on CT and MR imaging. Implications for radiotherapy treatment planning.

This paper deals with the impact MRI may have on radiotherapy treatment planning of brain tumors. The authors analyzed differences in size and position of treatment fields as indicated by three observers (two radiotherapists and one neuroradiologist) using CT or MR based radiotherapy planning procedures for cerebral-gliomas. Large differences in field size and position were found in non CT contrast enhancing tumors, all low grade gliomas. Small differences were found in contrast enhancing lesions including the high grade gliomas. We conclude that implementation of MRI in radiotherapy treatment planning leads to a greater precision in treatment fields for non CT contrast enhancing lesions.

Astrocytoma↗

PubMed1992

Analysis of machine-dependent and object-induced geometric distortion in 2DFT MR imaging.

Geometric distortion in MR imaging predominantly arises from the inhomogeneity of the static field and the nonlinearity of the gradients. It is the purpose of this paper to analyse the object and machine related contributions to geometric distortion in order to determine which corrections are necessary for attaining a specified precision. System related imperfections were measured by systematic variation of the strength, direction, and polarity of the read-out gradient in imaging experiments on a grid of cylindrical sample tubes. For the 1.5-T system used in this study, static field related errors up to 7 mm and gradient related errors up to 4 mm were observed (midcoronal plane, FOV 400-mm, G-read between 0.5 and 3.0 mT/m). Field related errors were shown to be inversely proportional to gradient strength, whereas gradient related errors turned out to be virtually independent of gradient strength. It therefore seems recommendable to always apply the strongest available selection and read-out gradients when geometric fidelity is given preference to signal-to-noise considerations. Correction of system related geometric distortions in MR images can readily be performed by table lookup. Object-induced distortions of the gradient fields were studied by experiments on a grid of sample tubes immersed into a cylindrical water bath of variable saline concentration. These experiments revealed a negligible influence of the object on the gradient error distribution, and lead to the conclusion that correction for the nonlinearity of the gradients only requires the application of system dependent correction factors. Object-related distortions of B0 were studied by conventional SE and fat-suppressed IR experiments on phantoms and human subjects. In these experiments the polarity of the read-out gradient was reversed. Subtraction images showed significant object-induced inhomogeneities of the static field at tissue-air interfaces and in the immediate vicinity of the object being imaged. A first attempt to correct for object related B0 inhomogeneities was made by contour analysis of the source images. At present this correction still has to be done manually.

Fourier Analysis↗

PubMed1992

Numerical analysis of the magnetic field for arbitrary magnetic susceptibility distributions in 2D.

We describe a numerical technique for calculating the 2D magnetic field in arbitrary magnetic susceptibility distribution. The technique we used is the explicit finite difference method with an addition of the Du Fort-Frankle algorithm. The proposed algorithm is unconditionally stable and has excellent convergence properties. For simple geometries, numerical results were compared against analytical solutions and appeared to be in excellent agreement.

Algorithms↗

PubMed1988

Human breast cancer in vivo: H-1 and P-31 MR spectroscopy at 1.5 T.

To assess the potential of in vivo magnetic resonance (MR) spectroscopy for breast cancer, hydrogen-1 and phosphorus-31 MR spectra of five malignant human breast tumors were compared with those of unaffected breast tissue. The water-to-fat ratio was high in the tumors (average, 2.2) but low in the unaffected tissue (average, 0.3). The P-31 spectrum of normal breast tissue showed low levels of phosphomonoesters (PMEs), inorganic phosphate, phosphodiesters (PDEs), and ATP. In addition, an intense phosphocreatine (PCr) signal was observed in breast tissue of young women: The relative intensities of the PCr and ATP signals had a mean value of 1.9. The tumor spectrum showed elevated levels of PMEs, Pi, and PDEs, while no PCr was seen (PCr/ATP less than 0.2). In two breast cancers treated with radiation therapy, resulting in a decrease of tumor volume of more than 50%, a similar change in the tumor P-31 spectrum was observed: An intense PCr signal developed (PCr/ATP = 1.1). Control experiments indicated that the appearance of PCr after radiation therapy was the result of a radiation-induced metabolic change in the tumor itself.

Adenocarcinoma, Mucinous↗

PubMedDate not supplied

Is the magnetic resonance imaging proton spin-lattice relaxation time a reliable noninvasive parameter of developing liver fibrosis?

During the development of liver fibrosis in rats by an individual dose-titrated CCl4 administration, hepatic proton spin-lattice relaxation time (T1) has been measured in vivo every 2 weeks for 8 weeks. Liver content of collagen, triglycerides and water has been measured biochemically in biopsy material. After 4 weeks of CCl4 treatment, T1 increased significantly and remained at the same level, whereas liver collagen reached its maximum at 8 weeks. It is concluded that, under our experimental conditions, increased hepatic T1 represents drug-induced edema and that hepatic T1 is not a reliable noninvasive parameter for developing liver fibrosis in vivo.

Animals↗

PubMedDate not supplied

Nonlinear display of NMR T1 and T2 images taking into account precision and visual perception.

This study deals with a two-step modification of the linear gray scales for the display of calculated T1 and T2 images. The first step, isoprecision display, links up the gray scales for T1 and T2 images and the estimated precisions of these parameters. For arbitrary experimental setups isoprecision gray scales can be calculated and implemented using table-lookup techniques. In the special case of a minimal dataset ratio images turn out to provide good approximations for isoprecision gray scales. The second step adapts the gray scales to the response of the human visual system by applying Weber's law.

Data Display↗

PubMedDate not supplied

Simple formulae for the calculation of RHO, T1 and T2 from a properly designed diagnostic NMR experiment.

The calculation of rho, T1 and T2 images from a minimal set of source images is considerably simplified if proper values for the sequence parameters are chosen. For the spin-echo technique a setup is suggested - a ratio of three between the effective repetition time of the T2- and the T1-weighted acquisitions - which not only produces the desired simplifications but which also is entirely compatible with normal diagnostic practice and close to optimum for two-point measurements.

Magnetic Resonance Imaging↗