Certification in Medical Physics Imaging,The Workforce and Training Models

The pathway to becoming a qualified medical physicist (QMP) in the imaging physics disciplines includes several certification organizations. Imaging QMPs play an essential role in the safe practice of the diagnostic disciplines, and their qualifications are necessary for compliance with federal bodies and professional accreditation organizations. The future demand for imaging QMPs is largely unknown, but professional organizations that represent these groups agree that efforts should be made to increase the number of matriculating trainees. The number of imaging residency programs that provide the necessary professional experience to enter the certification pathway has increased substantially in recent years. Most of these programs follow a traditional academic hospital-based training model, but guidance on program construction from the accrediting body permits flexibility. Existing training models for medical physics imaging also include consortiums of affiliate partners and private consulting service groups. In this article, the authors briefly review the certification pathways for imaging QMPs, workforce estimates, and training models.     

The novel use of a biodegradable stent placed by percutaneous transhepatic cholangiography for the treatment of a hepaticojejunostomy biliary leak following an extended left hepatectomy and pancreaticoduodenectomy

A 61-year-old man presented with jaundice, and subsequently underwent an extended left hepatectomy and pancreaticoduodenectomy for a cholangiocarcinoma invading the head of the pancreas. The patient developed sepsis due to a biliary leak at the hepaticojejunostomy. We describe the original use of a biodegradable stent, deployed via percutaneous transhepatic cholangiography into the Roux limb, resulting in good drainage and resolution of sepsis. The chief benefit of this procedure is the lack of need for subsequent removal as well as purported reduced biofilm accumulation. We believe this to be the first reported case of this type and the literature surrounding the subject is also discussed.     

Magnetic ordering in a vanadium-organic coordination polymer using a pyrrolo[2,3-d:5,4-d′]bis(thiazole)-based ligand

Here we present the synthesis and characterization of a hybrid vanadium-organic coordination polymer with robust magnetic order, a Curie temperature T_C of ∼110 K, a coercive field of ∼5 Oe at 5 K, and a maximum mass magnetization of about half that of the benchmark ferrimagnetic vanadium(tetracyanoethylene)_∼2 (V·(TCNE)_∼2). This material was prepared using a new tetracyano-substituted quinoidal organic small molecule 7 based on a tricyclic heterocycle 4-hexyl-4H-pyrrolo[2,3-d:5,4-d′]bis(thiazole) (C₆-PBTz). Single crystal X-ray diffraction of the 2,6-diiodo derivative of the parent C₆-PBTz, showed a disordered hexyl chain and a nearly linear arrangement of the substituents in positions 2 and 6 of the tricyclic core. Density functional theory (DFT) calculations indicate that C₆-PBTz-based ligand 7 is a strong acceptor with an electron affinity larger than that of TCNE and several other ligands previously used in molecular magnets. This effect is due in part to the electron-deficient thiazole rings and extended delocalization of the frontier molecular orbitals. The ligand detailed in this study, a representative example of fused heterocycle aromatic cores with extended π conjugation, introduces new opportunities for structure–magnetic-property correlation studies where the chemistry of the tricyclic heterocycles can modulate the electronic properties and the substituent at the central N-position can vary the spatial characteristics of the magnetic polymer.

Here we present the synthesis and characterization of a hybrid vanadium-organic coordination polymer with robust magnetic order, a Curie temperature T_C of ∼110 K, a coercive field of ∼5 Oe at 5 K.     

Microtubule reassembly in surface-activated platelets

It is generally accepted that a circumferential microtubule supports the discoid shape of resting platelets. The fate of the many-coiled polymer following platelet activation, however, has been a subject of considerable debate. Morphological investigations have suggested that the circumferential coils are constricted into tight rings around centrally concentrated organelles during platelet shape change. Biochemical studies employing colchicine-binding assays, on the other hand, have indicated that the bundle of microtubules dissolves almost completely within seconds after activation and reassembles in a new location one to four minutes later. The present study has accepted the latter hypothesis in order to examine the second part of the disassembly-reassembly theory proposed in biochemical studies. Platelets exposed to low temperatures sufficient to remove all microtubules were placed on glass slides and microscope grids to cause surface activation during rewarming. The combined stimuli of rewarming and surface activation might have been expected to cause more rapid assembly than warming alone or activation alone. This was not the case. Reassembly of microtubules during rewarming and simultaneous surface activation was not accelerated. In contrast to the constriction of microtubule rings observed during activation in control platelets, the diameters of coils that developed in chilled platelets one to two hours after rewarming and surface activation were twice those of control cells.     

Transcatheter atrial septal defect closure: modified balloon sizing technique to avoid overstretching the defect and oversizing the Amplatzer septal occluder.

The objective of this study was to evaluate a new technique of sizing atrial septal defects (ASDs) for transcatheter device closure. ASD closure using the Amplatzer septal occluder (ASO) device is commonly performed. Complications, including arrhythmias, pericardial effusions, and perforations, may be related to oversizing ASDs and choosing larger devices. Two methods were used to size ASDs using a compliant balloon. In some patients, the balloon was inflated until a waist was visible [(+)waist]; in others, only until no shunting was demonstrable by echocardiogram [echo; (-)waist]. The device was selected and implanted using standard procedure and echo guidance. One hundred seventeen patients underwent secundum ASD closure with an ASO device. There were 43 patients in the (-)waist group and 74 in the (+)waist group. All devices were implanted successfully. The initial echo ASD diameter was larger in the (-)waist group compared to the (+)waist group (P = 0.01). There was a smaller difference between the initial echo and balloon-sized ASD diameters in the (-)waist group (P < 0.02). ASO device size implanted (in mm greater than echo ASD diameter) was smaller in the (-)waist group (P < 0.01). There were 0/43 complications in the (-)waist group and 5/74 in the (+)waist group. The complete closure rate was the same in both groups. Sizing an ASD by inflating a compliant balloon just until shunting is eliminated, and not until a waist is visible, results in less overstretching of the ASD and selection of a smaller ASO device, achieving similar closure rates and potentially fewer complications.     

Congenital and surgical atrioventricular block within the His bundle

In three patients with congenital heart disease the site of atrioventricular (A-V) block was localized within the His bundle with the aid of His bundle electrograms. In one patient with first degree A-V block and normal QRS configuration, electrophysiologic studies revealed “split” His potentials. The other two patients had complete A-V block, and their His bundle electrograms revealed His spikes both proximal and distal to the site of block. One of the two patients, who had a pattern of left bundle branch block in the electrocardiogram, had surgically induced complete A-V block after repair of an ostium primum atrial septal defect. The other patient with congenital A-V block had a narrow QRS complex and, in addition to complete block within the His bundle, prolonged A-V nodal conduction time but no associated cardiac anomaly. Both patients with complete heart block required pacemaker insertion.

The natural history of intra-His bundle block is not known, and it is difficult to recommend appropriate therapy. More electrophysiologic studies are needed in patients with A-V block to determine the prognostic significance of such block or conduction delay in the His bundle.     

Clinical features and outcome in childhood T-cell leukemia-lymphoma according to stage of thymocyte differentiation: a Pediatric Oncology Group Study

The immunophenotypes of lymphoblasts from children with newly diagnosed T-cell acute lymphoid leukemia (T-ALL, n = 101) or T-cell non-Hodgkin lymphoma (T-NHL, n = 31) were analyzed to correlate stage of thymocyte differentiation with clinical features and outcome. The 67 boys and 34 girls with T-ALL were 1 month to 18 years old (median, 8 years) with leukocyte counts ranging from 2 to 810 x 10(9)/L (median, 55 x 10(9)/L). Eighteen of these patients were black, and 70 had a mediastinal mass. Twenty-six boys and five girls with a median age of 9 years (range, 1 to 20 years) had T-NHL. Seven of these patients were black, and 24 had a mediastinal mass. The distributions of thymocyte developmental stages (early [CD7+], intermediate [CD1+ and/or CD4+ and/or CD8+], and mature [CD3+]) in cases of T-ALL and T-NHL were significantly different: 34%, 43%, and 23% v 6%, 62%, and 32% (P = .02). A comparison of the patients' clinical features according to the maturational stage of thymocytes failed to disclose significant differences in the majority of characteristics studied. However, patients with mature-stage T-NHL, with or without the addition of subjects with mature-stage T-ALL, were less likely to have a mediastinal mass (P = .02 for both comparisons). Those with intermediate-stage T-cell malignancy (T-ALL and T-NHL combined) were the subgroup most likely to have a mediastinal mass (P = .01). Response to remission induction therapy was significantly worse in the T-ALL subgroup with an early-stage phenotype: a failure rate of 21% v 0% and 6% for the two more differentiated phenotypic subgroups (P = .007). Event-free survival was not affected by thymocyte maturational stage in cases of either T-ALL or T-NHL. Despite evidence of clinical heterogeneity among the maturational stages of T-cell malignancies in children, these developmental subdivisions do not appear to be critical determinants of outcome once remission is achieved. We conclude that such phenotypes need not be included in the stratification plans for clinical trials using common induction treatment.