Biomedical subjects

A S Alaamer

Publications and source records attributed to A S Alaamer.

5 recordsLinked to original sources

PubMed1998

A rule based method for context sensitive threshold segmentation in SPECT using simulation.

Robust techniques for automatic or semi-automatic segmentation of objects in single photon emission computed tomography (SPECT) are still the subject of development. This paper describes a threshold based method which uses empirical rules derived from analysis of computer simulated images of a large number of objects. The use of simulation allowed the factors affecting the threshold which correctly segmented objects to be investigated systematically. Rules could then be derived from these data to define the threshold in any particular context. The technique operated iteratively and calculated local context sensitive thresholds along radial profiles from the centre of gravity of the object. It was evaluated in a further series of simulated objects and in human studies, and compared to the use of a global fixed threshold. The method was capable of improving accuracy of segmentation and volume assessment compared to the global threshold technique. The improvements were greater for small volumes, shapes with large surface area to volume ratio, variable surrounding activity and non-uniform distributions. The method was applied successfully to simulated objects and human studies and is considered to be a significant advance on global fixed threshold techniques.

Algorithms↗

PubMed1996

Iodine-131-metaiodobenzylguanidine dosimetry in cancer therapy: risk versus benefit.

UNLABELLED: In the treatment of neural crest tumors, such as pheochromocytoma, with[131I]MIBG, bone marrow toxicity limits the amount of administered activity and, thus, a therapeutically useful tumor dose. METHODS: We calculated tumor doses in a series of diagnostic studies with [123I]MIBG using accurate quantification of SPECT and planar scintigraphy. By extrapolating diagnostic results to therapeutic activities of [131I]MIBG, we could compare the results with whole-body doses from a series of therapies. RESULTS: The tumor dose was DT = 2.2 mGy MBq(-1) (median value of 27 measurements, range 0.04 < or = DT < or = 20 mGy MBq(-1) and the whole-body dose in a series of 16 patients undergoing 50 therapies was DWB = 0.12 +/- 0.04 mGy MBq(-1) (mean +/- s.d.). The therapeutic ratio varied between 130 to below 10 in some patients. CONCLUSION: The results were compared with published data. We found clearly skewed distribution of tumor doses, with a majority of tumors receiving only a few mGy per MBq administered activity. In some patients, however, doses did reach 20 mGy MBq(-1).

3-Iodobenzylguanidine↗

PubMed1996

Influence of collimator characteristics on quantification in SPECT.

UNLABELLED: Accurate, absolute quantification of activity in SPECT depends on the counting sensitivity of the gamma camera collimator system and on the contribution of the tail of the point spread function (PSF) that contains both scattered radiation and septal penetration. METHODS: These factors were studied for the radionuclides 99mTc, 131I and 123I on different cameras and collimators. The ability of the geometric mean line source scatter function subtraction technique to correct for the effect of the tail of the PSF was investigated in a computer simulation study with 99mTc and a physical phantom study with 123I. RESULTS: The sensitivities of 99mTc collimators were relatively constant with distance in air whereas those of 123I and 131I decreased considerably. For these radionuclides the contribution of the PSF tail was also increased as compared to 99mTc. The geometric mean line source scatter function subtraction technique was confirmed as being able to correct effectively for this factor. CONCLUSION: Collimator design affects both the fall off of sensitivity in air and the tail of the PSF. Attention to correction of these factors enables accurate quantification.

Gamma Cameras↗

PubMed1994

Evaluation of the factors affecting the accuracy and precision of a technique for quantification of volume and activity in SPECT.

The use of the technique of maximization of interclass variance to determine the threshold level defining the volume of an object in single photon emission computed tomography (SPECT) and hence its activity has been evaluated in a variety of conditions. The influence of varying activity on volume assessment and varying volume on activity assessment were shown to be negligible. The effect of object shape for the range of shapes likely to be found in the body was also small. Non-uniformity of activity in the object caused an underestimation of volume and to a lesser extent its activity. However, with activity varying by 100% within the volume, volume was only underestimated by 10% and activity by 3%. The presence of activity surrounding the object caused an overestimation of volume which increased linearly with the relative level of surrounding activity. The object to surrounding activity concentration ratio could be estimated and therefore its effect corrected. The influence of nearby objects and methods of dealing with their effect on the technique are described. Activity concentrations in objects with uniform distribution assessed using total activity divided by total volume were shown to be more accurate than assessments from maximum voxel count rate for objects with a volume below 150 ml.

Humans↗

PubMed1993

Evaluation of a technique for the quantification of radioactivity and volume of an object using SPECT.

The technique of threshold determination using maximization of interclass variance (MIV) has been evaluated for the assessment of radioactivity and volume in single photon emission computed tomography (SPECT). The SPECT reconstruction incorporated scatter and attenuation correction using an attenuation map from computed tomographic (CT) images. The technique has been examined on a large number of phantom objects with both 99Tcm and 131I. Volume measurement of objects was performed using a variety of methods of applying the MIV technique. The standard error of volume estimation for the optimum method was 7.3 ml for 99Tcm and 15.3 ml for 131I. Activity was measured by expansion of the volume of interest representing the space occupied by the object to make allowance for limited SPECT resolution. The standard errors of the activity measurements were 0.22 MBq for 99Tcm and 0.24 MBq for 131I.

Evaluation Studies as Topic↗