What are computed tomography (CT) scans? How can they help detect cancer?

Cancers diagnosed: Most

Why performed: CT is a valuable tool for screening for cancer, locating tumors, performing guided biopsy, identifying cancer that has spread, staging cancer, planning and monitoring cancer treatment, and checking for cancer recurrence. CT can identify blood vessels that support a tumor, as well as the tumor’s shape, size, location, and volume. CT scans are used with procedures to diagnose cancer, such as needle-guided biopsies. They are used in cancer treatments, such as radiofrequency ablation and interstitial therapy.

CT images are archived in computers or printed form. Images are printed on film or with laser imaging. They can be sent and viewed online within a facility and can be compared for changes over time.

Conventional CT was developed in the early 1970s. CT uses controlled amounts of thin, high-energy radiation beams. Images are taken from a variety of angles. A computer calculates information about the images and produces a slice image of a specific area of the body. CT can be taken of the entire body or a specific section. Dye is used to enhance images to show more detail and contrast. The contrast dye can be swallowed, received intravenously, or administered in an enema.

CT has evolved to become faster and to use lower doses of radiation. Spiral or helical CT allows images to be collected quickly. The rapid process helps compensate for movements or breathing that otherwise can blur images. Additionally, spiral CT produces thinner slices of images that show even greater detail. A computer stacks the images to create three-dimensional, rotational pictures of a tumor. Spiral CT is especially useful for imaging liver, lung, and pancreatic cancer.

Recent technology allows doctors to use CT with endoscopy to create virtual endoscopy, virtual bronchoscopy, and virtual colonoscopy or CT colonography. The process uses a computer to create and manipulate three-dimensional images to create a “fly-through” view of an organ, as seen on endoscopy.

CT is used to guide surgeons precisely during procedures. CT is used with needle aspiration
biopsy for tumors, such as for breast cancer biopsies. The CT guidance eliminates the need for invasive exploratory surgery.

CT is used to guide certain radiation treatments. For example, interstitial therapy uses CT guidance to insert radioactive material into a tumor. CT is also used to create a three-dimensional image of a tumor to allow external beam radiation to precisely target the tissue and spare as much healthy tissue as possible.

Patient preparation: CT scans may not be appropriate for some people. Patients should let their doctor know if they have diabetes or kidney disease or if they are pregnant. Some facilities conduct a pregnancy test on all women prior to scanning because the radiation can be dangerous to a developing fetus. Children, patients with movement disorders, or patients that are claustrophobic may receive a mild sedative prior to the test. In extreme situations, people may be sedated if they are not able to remain still while the images are taken. Some CT machines may not be used for people that weigh more than three hundred pounds because of size parameters of the machinery. A small percentage of patients are allergic to contrast dye. Patients should let their doctor know if they are allergic or sensitive to contrast dye, iodine, or shellfish.

CT scans are outpatient procedures performed at a hospital radiology department or freestanding radiology center. Patients will receive instructions prior to their procedure, which vary depending on which procedure is conducted. Patients may be instructed not to eat or drink for several hours before the CT. Some patients need to use an enema or laxatives. Patients may need to drink a liquid contrast agent before arriving at the clinic or upon arriving at the clinic.

Patients wear an examination gown or robe for the procedure. They must remove metal objects that can interfere with the imaging process, such as jewelry, hearing aids, hair clips, glasses, or dentures.

Steps of the procedure: Patients are led into the imaging room. A radiology technologist conducts the CT. Patients lie on a narrow table. The technologist may use positioning devices to help patients maintain specific postures for the test. Head-stabilizing devices may be used for brain scans. Patients may be instructed to change positions throughout the procedure.

During the CT scan, the radiologist technician steps into a room that is separated by a glass partition. The radiologist is in constant contact with the patient via a microphone and intercom system. The radiologist technician operates the CT machine.

To take a CT, the table slides into the doughnut-shaped hole of the scanner. Patients must remain motionless while the images are taken. Patients are instructed to take a deep breath and hold it until they are told to exhale. The CT scanner has an X-ray component that emits beams at specific angles. The beams pass through the body and are detected by equipment on the opposite side. The equipment makes buzzing or clicking noises while the scanner is employed.

Patients receiving a contrast material may have a CT scan first, receive the contrast material, and then receive a final CT scan. An intravenous (IV) line is inserted into the hand or forearm to deliver injected contrast material. Contrast material may be swallowed. An enema is also used to insert contrast material for gastrointestinal-related CT scans. The contrast material may make patients feel temporarily warm or flushed.

The actual CT scan is short, but the preparation and positioning time makes the procedure last from about ten to thirty minutes. Spiral CTs are shorter in length. Patients are asked to wait until it is confirmed that the images are clear. Patients are observed for allergic reactions for a short time following the procedure.

After the procedure: There are usually no aftercare procedures following CT. If the patient has received sedating medication, a friend or relative must drive the patient home.

Risks: Patients may experience an allergic reaction to the contrast dye. The symptoms include hives, shortness of breath, nausea, wheezing, itching, or a bitter taste in the mouth. Severe allergic reaction or anaphylactic shock is a rare risk. Radiation from CT is higher than that of standard X rays. CT is not recommended for pregnant women.

Results: CT images are read by a radiologist and conveyed to the ordering doctor. The doctor may view the images as well. CT images depict anatomical structures in black, white, and shades of gray. Air, soft tissue, hard tissue, fluids, and the contrast agent show details that otherwise cannot be seen. Abnormal results show different characteristics from what is expected, such as tumors, cysts, cancer metastasis, tumor density, tumor composition, enlarged lymph nodes, or atypical fluid accumulations. In some cases, CT can help differentiate between types of tumors.

Applegate, Kimberly. “Pregnancy Screening of Adolescents and Women Before Radiologic Testing: Does Radiology Need a National Guideline?” Journal of American College of Radiology 4.8 (2007): 533–36. Print.

"Computed Tomography (CT) Scans and Cancer." National Cancer Institute. Natl. Cancer Inst., 16 July 2013. Web. 10 Sept. 2014.

Ishikawa, Susumu., et al. “Mass Screening of Multiple Abdominal Solid Organs Using Mobile Helical Computed Tomography Scanner: A Preliminary Report.” Asian Journal of Surgery 30.2 (2007): 118–21. Print.

Pearce, Mark S., et al. "Radiation Exposure from CT Scans in Childhood and Subsequent Risk of Leukaemia and Brain Tumours: A Retrospective Cohort Study." Lancet 4 Aug. 2012: 499–505. Print.

Sone, Shusuke., et al. “Long-Term Follow-up Study of a Population-Based 1996–1998 Mass Screening Programme for Lung Cancer Using Mobile Low-Dose Spiral Computed Tomography.” Lung Cancer 58.3 (2007): 329–41. Print.

Storrs, Carina. "How Much Do CT Scans Increase the Risk of Cancer?" Scientific American. Scientific American. 18 June 2013. Web. 10 Sept. 2014.

What is the polymerase chain reaction (PCR) method?

Definition

Polymerase
chain reaction (PCR)
is a rapid technique that enables the copying of desired
deoxyribonucleic acid (DNA) molecules. This technique consists
of three steps: denaturation, annealing, and extension, repeated in a cyclical fashion.

In step one of PCR, the reaction is exposed to temperatures as high as 194° to 201° Fahrenheit (90° to 94° Celsius). The high temperature helps to separate the two strands of the DNA template by breaking the hydrogen bonds that hold the two strands together. This melting of the DNA duplex is called denaturation.

The second step in PCR is called annealing or hybridization and requires short single-stranded DNA sequences called primers. The reaction uses two primers, one complementary to each strand of the original DNA duplex. The primers bind to their complementary sequences (or anneals) on the template DNA and provide the free 3’OH (hydroxyl) group that DNA polymerase needs to copy the DNA. This sets the stage for the last step in PCR, extension. During extension, the DNA polymerase uses deoxyribonucleotides (dNTPs) to build the complementary strand on the template DNA.

The foregoing set of three processes (making up a cycle) is typically repeated several times, about twenty to twenty-five cycles, to allow for an exponential increase in copies of the target gene. A simple formula can be used to calculate the yield (number of copies of the DNA or gene template). According to this formula, the number of gene copies after n cycles of PCR is 2 n. For example, if a person starts with a single copy of the gene, the yield will be 225 at the end of a PCR reaction with twenty-five cycles.

Background

PCR was discovered by Kary Mullis in 1983 while trying to
develop a method that would allow the sequencing of single nucleotide
polymorphisms (SNPs). SNPs are variations produced in DNA by
alterations to a single nucleotide and, therefore, serve as the absolute genetic
marker. Specifically, Mullis was trying to devise a rapid clinical assay for
genetic disorders such as sickle cell disease that are caused by
a single nucleotide polymorphism. DNA research in the 1980’s faced two major
challenges: not enough DNA and no easy way to separate a gene’s DNA from the
genomic DNA (1 milligram of DNA contains about 200,000 copies of a person’s target
gene). PCR offered a solution to both of these problems; one could amplify DNA
rapidly and could obtain as many copies as needed of the target gene alone.

The PCR Reaction

A PCR reaction, which is typically around 50 milliliters, requires the following: DNA template or target gene (10 femtograms to 10 milligrams), primers (0.1-1.0 millimolars each), dNTPs (200 millimolars each), DNA polymerase (0.2-2 units) and Tris buffer (pH8.0). Also, a PCR reaction requires MgCl2 (magnesium chloride), which is a cofactor for DNA polymerase. The DNA polymerase used in PCR is unique in that it can withstand high temperatures such as those used for melting DNA during the denaturation step. Before thermostable polymerases such as Taq and Vent were discovered, fresh polymerase had to be added after each round of PCR.

DNA in the cell is typically bound to packaging proteins such as histones. For a successful PCR reaction, the DNA template must be free of any inhibitory molecule (such as these packaging proteins) and thus easily accessible to the primers and polymerase. Therefore, once the DNA has been extracted from the cell, it is typically purified using some kind of enzymatic, mechanical, or chemical purification technique.

Next in the PCR process is the design of primer (forward and reverse primers). PCR primers are chemically synthesized nucleotide segments called oligonucleotides (or oligos) and are typically 18 to 30 bases long. Because primers are short sequences, misalignment can occur, leading to erroneous amplification. To minimize nonspecific binding, primers are preferably 18 to 21 bases long. The length of the PCR product is determined by the distance between the annealing sites of the two primers. Also important in primer design are factors such as guanine-cytosine content, polypurine or polypyrimidine stretches (multiples of any one nucleotide), the secondary structure of the primer (mutually complementary sequences within the primer can form “hairpin” structures), and the probability of a complementary sequence on the DNA residing anywhere except on the intended target gene (or region of amplification).

Once the PCR reaction is completed, the next important step is analysis of the PCR products with electrophoresis and various DNA intercalating dyes; this is followed by sequencing the amplimer (the amplified PCR product).

Impact

It is widely believed that since the discovery of the DNA double helix in the
1950’s, few discoveries have transformed the field of biology as rapidly as PCR.
This technique that allows the copying of millions of desired DNA beginning with
minute DNA samples has accelerated progress in forensics and in medical
diagnostics and has revolutionized biotechnology and biomedical
research.

Several modifications of the original PCR technique have been developed to meet the diverse needs of biomedical research. One such modification, qPCR (quantitative PCR), is frequently used in drug discovery to look for and assess new putative drug target sites in humans. The qPCR method is also used to determine the number of working copies of a specific gene, and this measure of gene expression is important in analysis of genetic disorders. For example, in STEP (single target expression profiling), qPCR is used to compare active gene numbers in affected versus healthy (unaffected) persons, allowing for the study of the progression or development of genetic disorders.

Bibliography

McPherson, M., S. G. Møller. PCR (The Basics). New York: Taylor & Francis, 2006. This is an excellent resource for those learning to set up and run PCR experiments.

Rabinow, P. Making PCR: A Story of Biotechnology. Chicago: University of Chicago Press, 1996. A great description of how the PCR technique has evolved since its development.

Van Pelt-Verkuil, E., A. van Belkum, and J. P. Hays. Principles and Technical Aspects of PCR Amplification. New York: Springer, 2008. A great resource for persons interested in furthering their understanding of PCR.

Did you enjoy reading the short story "Thank You M'am"? Explain why or why not?

The question of whether you enjoyed reading Langston Hughes’ story “Thank You, M’am” asks you to state an opinion. You would consider the emotions the story invokes in you while reading it before deciding whether you found the story enjoyable. After forming and stating your opinion, you would note story details you found pleasing. If you do not like the story, you would state your negative opinion and support it.

In my opinion, the story is enjoyable because it shows human compassion and understanding. After Roger attempts to steal Mrs. Luella Bates Washington Jones’ pocketbook she could have chosen to seek police intervention, instead she sees something of herself in Roger. She sees a young man who is a product of his difficult upbringing and environment, which she can identify with. She takes it upon herself to teach Roger a lesson in trust by confiding in him, feeding him, and giving him chances to prove himself to be trustworthy. For the short time they spend together, Roger meets Mrs. Jones’ expectations.

She shows Roger the ultimate kindness when she hands him the money for the shoes he wants so badly he reduced himself to stealing. Although Roger’s future is not revealed to the reader, it is evident Mrs. Jones would like to see her kindness carry over in his future decision making. For his part, Roger is rendered nearly speechless in his gratitude. The idea that one act of kindness can make a change in someone’s life makes this story appealing to me.

The boy wanted to say something else other than “Thank you, m’am” to Mrs. Luella Bates Washington Jones, but he couldn’t do so as he turned at the barren stoop and looked back at the large woman in the door. He barely managed to say “Thank you” before she shut the door. And he never saw her again.

What is the current state of affairs on Medicare and Medicaid? What has been accomplished and what still needs to be done?

The last major change to the American healthcare system occurred in 2010 after the passage of the Affordable Care Act (Obamacare). 

Here are some of the changes that were made:

Medicare: 

Obamacare changed Medicare in one clear way. All those earning an annual income of $85,000 or more are now paying slightly more for their Medicare Part D prescription drug coverage.

Overall, Medicare was mostly unchanged.

Medicaid:

Obamacare greatly expanded the requirements for Medicaid services. It is now 133% of the poverty line. However, the Supreme Court made this expansion opt-in only. This means that states can choose not to expand the program. Many conservative states have done this in opposition to the law.

In the states that have expanded, the federal government will fund 100% of the excess cost until the end of 2016, after which this funding gradually phases down to 90% by 2020.

Overall outlook

As a general rule right now, politicians and policy analysts disagree about the long term ability for the federal government to sustain our national healthcare programs.

Here are some commonly proposed changes:

Medicare:

Raising the eligibility age - as American life expectancy continues to rise, some propose raising the eligibility age from 65 to 67. This would certainly reduce costs, but others fear it would leave vulnerable Americans without the insurance that they need.

Raise premiums - this would also reduce costs, but some fear it could possibly price out the poorest seniors.

Raise payroll taxes - the generation of new revenue via an increase in payroll taxes would help fund Medicare into the future, but some worry that increasing taxes on income will be unpopular and discourage work.

Medicaid:

Complete expansion - if all of the states were to pass the Medicaid under Obamacare, it would significantly reduce the amount of Americans without health insurance. Due to political opposition to the law, this task will remain difficult for some time to come.

Local fixes - as Medicaid is a joint federal/state program, there are a wide variety of issues and solutions that need to come from state-level regulation and budgetary processes. As a result, besides stemming the rise of medical costs, there isn't a "one size fits all" solution to the program's challenges.

Conclusion:

Medical spending in America is dissimilar from other developed areas of the world. We have unique challenges, but also positive incentives.

The main challenge in the American healthcare system is costs. Medical costs have been rising for decades. And with an aging baby boomer population, the rising costs will continue to put burdens on our budget. 

There is debate as to what should be done about these future problems, but as these programs remain quite popular (specifically Medicare), it is quite hard to cut people's benefits.

In which ways does the identification of people to be killed in Act IV, Scene 1, of Julius Caesar affect the audience?

The cold-blooded manner in which Marc Antony discusses the elimination of political enemies is disturbing and ironic to audiences.

In Act IV, Scene 1, Rome is in crisis and on the brink of civil war, as Antony has predicted. Now the new triumvirate of Marc Antony, Octavius, and Lepidus is on the plains of Philippi where they will soon battle the forces of Brutus and Cassius. In this scene, however, Marc Antony and Octavius focus on their plan to eliminate their political enemies and steal legacies from other Romans.

As Marc Antony speaks with Lepidus, they go down the list of names marked for death, and Lepidus agrees to the death of his brother; Octavius asks Antony about another name, and Antony agrees to the death of his nephew. Then, Lepidus is sent to procure the will of Caesar so they are able to view some of the legacies given to the citizens and reduce them. 

After Lepidus departs, Antony treacherously remarks to Octavius that Lepidus is a "slight unmeritable man" and undeserving of sharing the triumvirate with them. Octavius argues that Lepidus is a "tried and valiant soldier," but Marc Antony's cold opinion of Lepidus as no more than his horse is disturbing. Further, he tells Octavius he has already sealed the fate of Lepidus with his mark.

These words and actions of the triumvirate, and especially those of Marc Antony are ironic because, in Act III, Antony was the one in Act III who questioned the honor of Brutus and the others who assassinated Caesar, concerned that they would become tyrannical. Now, however, it is Antony who has become tyrannical instead. Also, in Act III Antony has addressed the plebeians as inheritors of Caesar's wealth, but now he has their legacies taken from them or reduced. Ironically, too, the devious planning of the death of Lepidus and the civil disorder caused by Marc Antony and the others is much worse than Brutus's fears of Caesar.

What is the approximate "weight" of an astronaut on the Moon, if his mass is 80 kg? A. 128 N B. 784 N C. 50 N D. 176 N

Weight can be thought of as the gravitational pull a celestial body exerts on a given object or body and hence is dependent on the celestial body in question. In comparison, mass is a measure of the matter contained in the body and is a constant quantity. Since weight is a force, it can be calculated using Newton's second law of motion as:

F = m x a

where F is the force, m is the mass of the body and a is its acceleration. To calculate the weight, you must know the acceleration due to gravity. Acceleration due to gravity is a function of the celestial body the astronaut is on and hence weight will be different on each celestial body. The acceleration due to gravity on Earth is represented by "g" and has a value of about 9.8 m/s^2. In comparison, the value of acceleration due to gravity on the Moon is about 1/6 g and has a value of 1.6252 m/s^2. Hence the weight of the astronaut will be:

weight = mass x acceleration due to gravity

= 80 kg x 1.6252 m/s^2 = 130 N (approximately).

Among the given options, only choice (A) 128 N is close enough and hence is the correct choice.

Hope this helps. 

Explain what Giles’ dialogue reveals about what he thinks is behind the witch hunt in The Crucible.

In Act Three, Giles Corey, John Proctor, and Francis Nurse, all husbands of accused witches, come to the court in an effort to speak with Deputy Governor Danforth, the chief magistrate of the witch trials.  Proctor has brought his servant girl, Mary Warren, with them so that she can provide her testimony against the girls, and Corey has written an affidavit himself with his own testimony against Thomas Putnam.  

Giles claims that an "honest man" overheard Thomas Putnam saying that on the day his daughter, Ruth, accused George Jacobs of witchcraft, "she'd given [Putnam] a fair gift of land."  The reason Putnam might call the land a gift is that a convicted witch's property would go up for auction and anyone with the money could then purchase it.  According to Corey, no one besides Putnam has the money to buy such a large piece of land at auction; therefore, he believes that Putnam "coldly prompted [his] daughter to cry witchery upon George Jacobs," as Danforth puts it.  Therefore, Corey believes it is greed that is behind the trials, that Putnam is pulling the strings for his own gain.