CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	12 Months Ended
	Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2011
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (29,780,000)	$ (42,119,000)	$ (34,151,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation	3,435,000	2,769,000	2,837,000
Depreciation and amortization	1,087,000	908,000	652,000
Loss on early extinguishment of debt	1,696,000	0	0
Amortization of discount on notes payable and debt issuance costs	0	33,000	235,000
Amortization of expenses paid in shares of common stock	0	0	956,000
Common stock issued for services	0	0	40,000
Loss on sale of property	8,000	2,000	0
Changes in operating assets and liabilities:
Trade and other receivables, net	691,000	(964,000)	92,000
Government contract receivables	0	93,000	274,000
Inventories	(728,000)	1,673,000	(2,161,000)
Prepaid expenses and other current assets, net	86,000	158,000	95,000
Other non-current assets	2,000	789,000	(7,000)
Accounts payable	(691,000)	(601,000)	608,000
Accrued clinical trial site and related fees	(1,181,000)	(181,000)	984,000
Accrued payroll and related expenses	1,114,000	1,013,000	(168,000)
Deferred revenue	451,000	(2,237,000)	3,843,000
Deferred government contract revenue	0	0	(78,000)
Customer deposits	3,194,000	3,106,000	(859,000)
Other accrued expenses and current liabilities	24,000	(62,000)	372,000
Other long-term liabilities	(334,000)	(258,000)	(26,000)
Net cash used in operating activities	(20,926,000)	(35,878,000)	(26,462,000)
CASH FLOWS FROM INVESTING ACTIVITIES:
Property acquisitions	(853,000)	(1,554,000)	(912,000)
Decrease (increase) in other assets	102,000	383,000	(435,000)
Net cash used in investing activities	(751,000)	(1,171,000)	(1,347,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net of issuance costs of $1,232,000, $1,151,000, and $769,000, respectively	39,522,000	33,179,000	33,087,000
Proceeds from issuance of notes payable, net of issuance costs of $251,000	14,749,000	0	0
Proceeds from issuance of common stock under Employee Stock Purchase Plan	534,000	236,000	134,000
Proceeds from exercise of stock options	96,000	0	44,000
Principal payments on notes payable	(15,000,000)	(1,333,000)	(2,000,000)
Payment of final fee on notes payable	(975,000)	0	0
Principal payments on capital leases	(78,000)	(75,000)	(62,000)
Net cash provided by financing activities	38,848,000	32,007,000	31,203,000
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	17,171,000	(5,042,000)	3,394,000
CASH AND CASH EQUIVALENTS, Beginning of year	18,033,000	23,075,000	19,681,000
CASH AND CASH EQUIVALENTS, End of year	35,204,000	18,033,000	23,075,000
SUPPLEMENTAL INFORMATION:
Interest paid	46,000	68,000	301,000
SCHEDULE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Fair market value of warrants issued in connection with notes payable	470,000	0	0
Accounts payable for purchase of property	20,000	47,000	300,000
Property acquired under capital lease	0	0	180,000
Other asset in exchange for future services	$ 0	$ 0	$ 233,000