The role of pure iterative reconstruction in conventional dose CT enterography

PURPOSE

Pure iterative reconstruction (Pure IR) has been proposed as a solution to improve diagnostic quality of low dose CT images. We assess the performance of model based iterative reconstruction (MBIR) in improving conventional dose CT enterography (CTE) images.

METHODS

43 Crohn's patients (27 female) (38.5 ± 12.98 years) referred for CTE were included. Images were reconstructed with pure IR (MBIR, General Electric Healthcare) in addition to standard department protocol (reconstructed with hybrid iterative reconstruction (Hybrid IR) [60% filtered back projection/40% adaptive statistical IR (General Electric Healthcare)]. Image quality was assessed objectively and subjectively at 6 anatomical levels. Clinical interpretation was undertaken in consensus by 2 blinded radiologists along with 2 non-blinded readers ('gold standard'). Results were analyzed using Statistical Package for Social Scientists.

RESULTS

Mean effective radiation dose was 6.05 ± 2.84 mSv (size specific dose estimates 9.25 ± 2.9 mGy). Objective and subjective assessment yielded 6106 data points. Pure IR images significantly outperformed those using standard reconstruction techniques across all subjective (p < 0.001 for all comparisons) (noise, contrast resolution, spatial resolution, streak artifact, axial diagnostic acceptability, coronal diagnostic acceptability) and objective (p < 0.004) (noise, signal-to-noise ratio) parameters. Clinical reads of the pure IR images agreed more closely with the gold standard reads than the hybrid IR image reads in terms of overall Crohn's activity grade (κ = 0.630, 0.308) and detection of acute complications (κ = 1.0, 0.896). Results were comparable for bowel wall disease severity assessment (κ = 0.523, 0.593).

CONCLUSIONS

Pure IR considerably improves image quality of conventional dose CTE images and therefore its use should be expanded beyond low dose protocols to improving image quality at conventional dose CT imaging.

The DNA sequence and biological annotation of human chromosome 1

The reference sequence for each human chromosome provides the framework for understanding genome function, variation and evolution. Here we report the finished sequence and biological annotation of human chromosome 1. Chromosome 1 is gene-dense, with 3,141 genes and 991 pseudogenes, and many coding sequences overlap. Rearrangements and mutations of chromosome 1 are prevalent in cancer and many other diseases. Patterns of sequence variation reveal signals of recent selection in specific genes that may contribute to human fitness, and also in regions where no function is evident. Fine-scale recombination occurs in hotspots of varying intensity along the sequence, and is enriched near genes. These and other studies of human biology and disease encoded within chromosome 1 are made possible with the highly accurate annotated sequence, as part of the completed set of chromosome sequences that comprise the reference human genome.

Sequence analysis and transcript identification within 1.5 MB of DNA deleted together with the NDP and MAO genes in atypical Norrie disease patients presenting with a profound phenotype

Mutations at the Norrie disease gene locus, NDP, manifest in a broad range of defects. These range from a relatively mild, late-onset, exudative vitreoretinopathy to congenital blindness and sensorineural deafness combined, in some cases, with mental retardation. In addition, extensive deletions involving the NDP locus, located at Xp11.3, the adjacent monoamine oxidadase genes MAOA and MAOB, and additional material, result in a more severe pattern of symptoms. The phenotypes include all or some of the following; mental retardation, involuntary movements, hypertensive crises and hypogonadism. We extended an existing YAC contig to embrace the boundaries of three of the largest deletions and converted this into four PAC contigs. Computer analysis and experimental data have resulted in the identification of several putative loci, including a phosphatase inhibitor 2-like gene (dJ154.1) and a 250-bp sequence which resembles a homeobox domain (dA113.3), 1.2 Mb and 400 kb respectively from the MAO/NDP cluster. The pattern of expression of dJ154.1 suggests that it may represent an important factor contributing to the complex phenotypes of these deletion patients. Hum Mutat 17:523, 2001.

Isolation of high-affinity monomeric human anti-c-erbB-2 single chain Fv using affinity-driven selection

The use of antibodies to target tumor antigens has had limited success, partially due to the large size of IgG molecules, difficulties in constructing smaller single chain Fv (scFv) antibody fragments, and immunogenicity of murine antibodies. These limitations can be overcome by selecting human scFv directly from non-immune or semi-synthetic phage antibody libraries; however, the affinities are typically too low for therapeutic application. For hapten antigens, higher-affinity scFv can be isolated from phage antibody libraries where the VH and VL genes of a binding scFv are replaced with repertoires of V genes (chain shuffling). The applicability of this approach to protein binding scFv is unknown. For this work, chain shuffling was used to increase the affinity of a non-immune human scFv, which binds the glycoprotein tumor antigen c-erbB-2 with an affinity of 1.6 x 10(-8) M. The affinity of the parental scFv was increased sixfold (Kd = 2.5 x 10(-9) M) by light-chain shuffling and fivefold (Kd = 3.1 x 10(-9) M) by heavy-chain shuffling, values comparable to those for antibodies against the same antigen produced by hybridomas. When selections were performed on antigen immobilized on polystyrene, spontaneously dimerizing scFv were isolated, the best of which had only a slightly lower Kd than wild type (Kd = 1.1 x 10(-8) M). These scFv dimerize on phage and are preferentially selected as a result of increased avidity. Compared to scFv which formed only monomer, dimerizing scFv had mutations located at the VH-VL interface, suggesting that VH-VL complementarity determines the extent of dimerization. Higher-affinity monomeric scFv were only obtained by selecting in solution using limiting concentrations of biotinylated antigen, followed by screening mutant scFv from bacterial periplasm by koff in a BIAcore. Using the proper selection and screening conditions, protein binding human scFv with affinities comparable to murine hybridomas can be produced without immunization.

Cloning and DNA sequence of double-stranded copies of haemagglutinin genes from H2 and H3 strains elucidates antigenic shift and drift in human influenza virus

Double-stranded DNA copies of the RNA gene coding for the haemagglutinin glycoproteins from human H2 and H3 pandemic strains of influenza virus have been cloned. DNA sequence analysis provides the first reported complete nucleotide sequence of an H2 haemagglutinin gene and a partial sequence (45%) of the H3 gene. The H2 haemagglutinin gene consists of 1,773 nucleotides containing an uninterrupted coding sequence of 1,686 nucleotides specifying a protein of 562 amino acids. Comparison of the amino acid sequences of these haemagglutinins with those of other H3 and avian strains reveals the extent of sequence changes in antigenic shifts and drifts.