Human Health and Disease

Radiography uses X-rays and computed tomography (CT) uses X-rays to generate a three-dimensional image of the internal organs; X-rays are ionising radiations and can themselves damage DNA.
Histopathological study (biopsy) requires a piece of the suspected tissue to be cut out, so it is an invasive technique.
MRI uses strong magnetic fields and non-ionising radiations to detect pathological and physiological changes in living tissue accurately.
Since MRI involves neither ionising radiation nor surgery, it is the safest of these.
Hence the safest technique is magnetic resonance imaging (MRI).

$Plasmodium$ enters the body as sporozoites, which first multiply in the liver cells and then attack the red blood cells.
Inside the RBCs the parasite multiplies asexually; the RBCs then rupture, releasing the new parasites (merozoites) that enter fresh RBCs.
The rupture of RBCs is associated with the release of a toxic substance, haemozoin, which is responsible for the chill and high fever recurring every three to four days.
Sporozoites are not released from RBCs, and the destruction of gametocytes is not the cause of the fever.
Hence chill and fever occur when the parasite, after rapid multiplication inside RBCs, ruptures them and releases the stage that enters fresh RBCs.

Plague is caused by the bacterium $Yersinia\ pestis$.
Vaccines against plague have been prepared from killed bacteria (formalin-inactivated or heat-killed suspensions of virulent bacteria) and from live attenuated, avirulent strains.
Synthetic capsular polysaccharide vaccines are available for other bacterial diseases, such as pneumonia caused by $Streptococcus\ pneumoniae$ and $Haemophilus\ influenzae$, and meningitis caused by $Neisseria\ meningitidis$.
Such a polysaccharide vaccine is not available for plague.
Hence synthetic capsular polysaccharide material cannot be used for preparing vaccines against plague.